STUDIES ON THE LIFE HISTORY OF THE ROBIN (Turdus migratorius Linnaeus) By John Frederick Mehner AN ABSTRACT Submitted to the School for Advanced Graduate Studies Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Zoology 1958 Approved John Frederick Mehner From 1953 through 1957, the life cycle of the robin was studied in Pittsburgh, Pennsylvania, and in East Lansing, Michigan. In Pittsburgh the and first spring migrants appeared between mid-February the first part of March, Fall migration continued until mid-November when usually a small wintering population remained. Of 29 winter recoveries of robins banded in East Lansing, 69 per cent were betv;een the latitudes of 30° and 35° N.. Several threat displays and postures, some similar or identical to ones that have been described for Catharus and Hylocichla. are used to in­ timidate other robins and other species. The many vocalizations were recorded under a variety of conditions. The whisper song serves as a threat, and functions in the establishment and maintenance of for the declaration of thepairing bond, while the carolling song is probably territory. In two summers the beginning of song cessation v;as evident by the first part of July. the first week of August. Last songs were heard In Pittsburgh a period of song resumption usual­ ly followed in early autumn. The populations of robins ranged from 12 pairs per 100 acres in an aspen community to 120 pairs per 100 acres in residential areas. In East Lansing DDT and other insecticides appear to be a major factor in declin­ ing robin populations. Maximum territory, determined by 40 to 50 consecutive observations at five-minute intervals, was about 2.5 acres in three instances. Utilized territories, determined by 20 or more irregularly spaced observations, ran­ ged in size from ,24 to .87 acres in 12 cases. There appeared to be a John Frederick Mehner correlation between territory size and population density. The first nest building began after a rise in temperature, followed by peaks of nesting in early and late spring. struction of 12 nests was 4.5 days. The average time for con­ The nesting heights in residential areas were greater than those found in undisturbed areas by other workers. No preferred height was evident for individual females, but the second nest was usually higher than the first. An undescribed species of Protocalliphora was found in 40 per cent of 20 nests collected in Pittsburgh, but this parasite did not markedly affect nesting success. The mean clutch size for 42 nests in Pittsburgh was 3.4 * .11, and for 13 in East Lansing it was 3.5 * .18. evident in June. days. A decrease in clutch size was The mean incubation period for 12 clutches was 12.9 Z ,19 Several observations of males sitting on eggs were made. The mean extent of the nestling period for 37 individuals was 13.9 * .16 days. During approximately 16 hours of observations, feedings to nestlings averaged 6.4 per hour. Adults ate excreta in varying degrees at the nest. The mean extent of the fledgling period for 15 broods was 14.9 * .74 days. It was divided into three stages: Hiding Stage (0-3 days after fledging), Early-flying Stage (4-6 days after fledging), and Semi-dependent Stage (7 days after fledging until the young become independent). Three / sets of fledglings confined their activities to areas ranging from one acre to 5.8 acres. Nesting success averaged 66.7 per cent for 36 nests in East Lansing as well as for 48 nests in Pittsburgh. First nests in conifers were more John Frederick Mehner successful (75 per cent) than those in deciduous trees (44 per cent)* Of 161 eggs, 70*8 per cent hatched and 49.1 per cent produced fledglings. Depending primarily upon eyesight for obtaining food, the robin probes in the ground for food from either a crouched position or a normal posture. After breeding, robins feed in.flocks, usually in woodlots adjacent to open areas, where there is a good supply of fruiting shrubs and exposed leaf litter. Three night roosts were studied: one in shade trees along city streets, one in a second growth woods, and another on a shrubby embankment in a city park. groups. Robins usually flew to roosts singly or in small, straggling With the advent of darkness, they moved into the roosts in increas­ ing numbers. STUDIES ON THE LIFE HISTORY OF THE ROBIN (Turdus migratorius Linnaeus) By John Frederick Mehner Submitted to the 3chool for Advanced Graduate Studies Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Zoology 1958 ProQ uest Number: 10008579 All rights reserved INFORM ATION TO ALL USERS The quality o f this reproduction is dependent upon the quality o f the copy submitted. In the unlikely event that the author did not send a com plete m anuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQ uest 10008579 Published by ProQ uest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This w ork is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 i TABLE OF CONTENTS Page I NTRODUCTION......................................................... Soope and Purpose of Study ..................... . . . . . . . . Taxonomic Status of the R o b i n ................ Methods of Study • • • « • ..................... 1 1 1 . . . . . . . . A c k n o w l e d g m e n t s ........ • ...................... 2 3 DESCRIPTIONS OF STUDY A R E A S ......................................... Location • •... . ............ 5 5 Climatic C o n d i t i o n s .............. . . . . 5 F l o r a .................. 10 F a u n a ........................................................... 12 DISTRIBUTION AND M I G R A T I O N ........................................... 14 Seasonal Distribution .......................................... 14 M i g r a t i o n ...................................................... 17 HOSTILE B E H A V I O R .................................................... 22 M A T I N G ............................................................... 28 Pair F o r m a t i o n .................................................. 28 C o p u l a t i o n ......................... 30 THE SONG C Y C L E ........................... 32 Description of Songs ............................................ 32 Song in Relation to the Breeding Cycle 33 Daily Cycle of Song Song Perches Song Cessation ................ • • • • ................................... .................... ................................................ Resumption of Song in the Autumn 36 37 38 42 ii Page CALL N O T E S ........................................................... 44 P O P U L A T I O N S ......................................................... 48 In Wooded Areas In Open Areas . ......... • ............ . . . . . . . . . . . • • • . • • • • • • • • . . ............. . . . . 48 49 T E R R I T O R Y ............................... .. ......................... 60 Territorial B e h a v i o r ..................... . ..................... 60 Size of Territories 61 . . . • • • • • .......... •• ..............• NESTS AND NEST BUILDING ................................. Span of Nesting S e a s o n ................ Selecting the Nest Site Nest Site . . . . . . Nesting Height Nest Construction 69 • • . . . • • • • • • • • .................... . . . . . . . . . . . ........................... • • • • * • • . 69 73 74 80 ............... 82 Arthropod Fauna of Robin Nests ... 89 E G G S .............. .................... 92 D e s c r i p t i o n .................. 92 Oviposition ............. . . . . . . . . 92 Clutch S i z e .................................................... 93 Incubation ............... 93 Hatching • • * . . . • • . . > • • « • ............. • THE Y O U N G ........................................................... Physical Development .................... • • Attentive Behavior of Adults at the Nest Extent of Nestling Period .................... 96 98 98 98 103 Interval Between B r o o d s .................. 105 Fledgling P e r i o d ................ 106 iii Page NESTING SUCCESS ..................................................... 113 FOOD AND FEEDING B E H A V I O R .......................................... 116 Food Materials Feeding Behavior ........................................ . . . . . . . . Communal Feeding Areas Drinking Water .......... ............................. .............. . . . 116 117 118 120 R O O S T I N G ........................................................... 122 S U M M A R Y .................. 127 APPENDIX I: T a b l e s ................................................ 131 P l a t e s .............................................. 177 LITERATURE C I T E D .................................................. 186 APPENDIX II: LIST OF FIGURES Page Figure I . Study Area 1, in Castle Shannon, a suburb of Pittsburgh* 6 Study Area 2, in Mount Lebanon, a suburb of Pittsburgh. 7 Figure 3. Study Area 3, in East Lansing. 8 Figure 4* Robins observed at a roost in Highland Park, Pittsburgh, during the winter months from 1955to 1957. 15 Foreign recoveries of robins banded in East Lansing, 1925-1942. 18 Michigan recoveries of robins banded in East Lansing, 1928-1942. 21 Figure 2 . Figure 5. Figure 5. Figure 7. Song cessation of the robin at Pittsburgh in 1955. 40 Figure 8. Song cessation of the robin at East Lansing 41 in 1956. Figure 9. The breeding population of Area 1 in April and May, 1956. 50 Figure 10. The breeding population of Area 2 in April and May, 19 55. 51 Figure 11. The breeding population of Area 3 in July, 1956. 52 Figure 12. The breeding imputation of Area 3 in April and the first part of May, 1957. 53 The breeding population of Area 3 from mid-May through Pune, 1957. 54 Counts of robins in the Horticultural G-ardens, Michigan State University. 56 Successive territories of M4 and F6 in Area 1 during two nestings in the spring of 1956. 62 Successive territories of M2 and F3 in Area 1 during two nestings in 1955. 63 Figure 13. Figure 14. Figure 15* Figure 16. Figure 17. Territory of the 56-24 pair in Area 3 during incubation. Figure 18. Territory of the 56-24 pair in Area 3 during the period when young were being fed in thenest* 65 66 V Page Territory of the 57-13 pair in Area 3 during incubation. 67 Robin nesting cycle in Area 1. 70 Robin nesting cycle in Area 2. 71 Robin nesting cycle in Area 3 in 1957. 72 Nesting sites of FI in Area 2 from 1954 through 1956. 77 Nesting sites of F3 in Area 1 from 1954 through 1956. 78 Nesting sites of F4 (nests 56-3 and 56-21) and F6 (55-22 and 56-13) in Area 1 in 1955 and 1956. 79 Nests in their first day of construction in and around Areas 1 and 2 in 1954. 83 Nests in their first day of construction in and around Areas 1 and 2 in 1956. 84 Nests in their first day of construction in and around Area 3 in 1957. 85 Nest-building activities of the 54-6 female in Area 1. 88 Daily changes in weights of the robins in nest 54-44. 99 The composition of robin flocks arriving at the Ingram roost in Pittsburgh on the evenings of August 27 and September 11, 1953. 124 Arrival of robins at the Highland Park roost during five evenings in August, September and October, 1955. 125 X INTRODUCTION Scope and Purpose of StudyVarious aspects of the life cycle of the robin (Turdus migratorius) have been studied by several workers. Breeding behavior and nesting have been studied by Howell (1942) and Young (1955), territorial behavior by Young (1951), local and migratory movements by Speirs (1946, 1953, 1956), and mortality rates and longevity by Farner (1945, 1949). Innumerable short papers and notes concerning this species have been published as well. This study is concerned with the general life cycle of the robin in residential areas where it is common. This is in contrast to previous studies which have been concerned largely with robins found in cemeteries, parks, and on campuses. Consequently, data on nesting populations of robins in residential areas have been lacking. Other studies have includ­ ed little on late stages of the breeding cycle when adults are feeding young out of the nest. ful attention here. This aspect of the life cycle has been given care­ The current study also supplements existing literature on territorial behavior, courtship, mating, nesting, feeding behavior, vocalizations, and flocking. The seasonal distribution of the robin in Pittsburgh, Pennsylvania, is also considered. Taxonomic Status of the Robin North American robins are classified in the family Turdidae together with the solitaires, the bluebirds, and the other thrushes. The range of Turdus migratorius. according to the A. 0. U. Check-List of North American Birds (1957:431), is: 2 ”From the limit of trees in northern Alaska, northern Canada, and New­ foundland south to southern Mexico and the shores of the Gulf of Mexico, In winter to southern Baja California, Guatemala, and southern Florida,” In this check-list Turdus migratorius is divided into five subspecies, T* m. migratorius is the breeding subspecies in the areas where this study was conducted. T. m. nlgrideus breeds in northeastern Canada, T. jn. achrusterus in the southern parts of the United States, JT. m. caurinus in northwestern North America, and _T. m. propinquus in western United States and Canada. The San Lucas robin (Turdus confinis), in southern Baja Cali­ fornia, is listed as a separate species in the current check-list. Many other species of Turdus occur in Mexico and southward. Methods of Study The data for this study were gathered from August, 1953, through October, 1957, in Pittsburgh, Pennsylvania, and in East Lansing, Michigan. Many of the observations were made in three study areas, two in Pittsburgh and one in East Lansing. Observations were recorded in field notebooks and on mimeographed maps of the study areas, which were carried in the field at all times* Nests were designated by hyphenated numbers— i.e., 54-1, 55-6, etc,— the first part indicating the year of the active nest. In order to recognize individual robins in the field, I placed alumi­ num government bands as well as combinations of red, yellow, green and blue celluloid bands on the tarsi of 71 birds. The males are referred to as Ml, M2, etc., the females as FI, F2, etc., and the young as Yl, Y2, etc.. Robins were caught with collapsible flat traps, described by Lincoln (1947:15). In the Pittsburgh study areas, sliced apples and pieces of bread proved to be particularly effective baits from the time of the rob­ ins’ arrival in early spring until mid-June. For unknown reasons, robins were not attracted by this bait during the summer months, and neither bread 3 nor apples were successful in the East Lansing study area at any time of the year. However, water dripping into a trap from a container suspended above it proved effective in East Lansing during the summer months. It should be pointed out that some residents in the Pittsburgh study areas regularly placed various food items on the ground for birds, and this could well be the reason for the difference in trapping success in the two local­ ities. trap. Often there was no hesitation on the part of a robin to enter a On June 1, 1954, a collapsible trap was placed in a backyard and baited with apples. Five minutes later an adult entered the trap. By June 18, however, apples were not taken in any of the traps. In an attempt to elicit threat displays and/or courtship behavior, dummy robins were placed in areas where robins were nesting, often in the immediate vicinity of a nest, and tape recordings of songs and various call notes were played at intervals. In his study of the English robin (Erith- acus rubecula). Lack (1953) used stuffed dummies to good advantage. In his study of the genera Catharus and Hylocichla, Dilger (1956) used record­ ed vocalizations and/or models. Acknowledgments I wish to express ray deep appreciation to Dr. George J. Wallace for his helpful advice and guidance while this study was being conducted and for his critical reading of the manuscript. I am indebted to Mr. William Malcolm for his help in the preparation of the figures, and to Mr. Bernard Yan Cleve who gathered many of the data at the Highland Park Roost in Pittsburgh. Many thanks are due to the residents of the study areas for permission to use their grounds for observations. Of these, Mrs. Ruth Durkee, Mr. Edwin Graff, the late Mrs. George Graff, Dr. and Mrs. E. J. Miller, and Mr. and Mrs. Byron Townsend were particularly helpful. I am 4 grateful to Mrs. Dale Henderson for help v/ith the bird banding files at Michigan State University, and to Mr. C. C. Ludwig for the use of his bird banding records. Dr. William Drew, Head of the Department of Botany and Plant Pathology at Michigan State^University, advised me on the use of botanical nomenclature. Dr. Gordon Guyer of the Entomology Department at Michigan State Uni­ versity, and Dr. George Wallace of the Carnegie Museum, Pittsburgh, were helpful in the identification of insect materials. I also wish to extend my thanks to Dr. E. W. Baker, Mr. H. W. Capps, Dr. P. W. Oman, Dr. Curtis Sabrosky and Dr. Alan Stone, all of the Insect Identification and Parasite Introduction Section, U. S. Department of Agriculture, for the identifica­ tion of arthropod materials. Dr. Kenneth Parks and Mr. W. E. Clyde Todd gave me permission to use publications in the Ornithology Laboratory at Carnegie Museum. I am grateful to Mr. Gerlach of the Urban Planning De­ partment, Michigan State University, for permission to use planimeters. I also wish to express my thanks to the many students and friends who assisted me in the field and who furnished me with observations. 5 DESCRIPTIONS OF STUDY AREAS Location Areas 1 and 2 were located in Pittsburgh (40° 30* N., 80° 13* W., elevation 1151 feet). Area 3 was located in East Lansing (42° 4 4 f N., 84° 29* W., elevation 856 feet). Area 1 (Figure 1) was on the edge of the business district of Castle Shannon, a suburb of Pittsburgh. Approximately five acres in extent, it was bounded on the north by the business district, on the south by an un­ paved road, and on the west by a paved street. A gully with a stream flow­ ing in a northeasterly direction marked the other boundary. Area 2 (Figure 2) was located in Mount Lebanon, also a suburb of Pittsburgh. Irregular in shape, it covered approximately 7,5 acres. Its northern limits were determined by property lines while a steep slope marked the southern boundary toward the west• Mount Lebanon park was on the west, and paved streets completed the other boundaries. Area 3 (Figure 3) was adjacent to the eastern end of the Michigan State University campus. More or less rectangular in shape, it was approx­ imately 15.5 acres in extent. Paved streets bounded it on the north and the west, and the Red Cedar River on the south while property lines formed the eastern limits, which were indicated in part by various trees and shrubs. Climatic Conditions The following sumrarizes some climatological information about Pitts­ burgh and East Lansing, as taken from data gathered by the Weather Bureaus in both cities over a period of 45 years. Figure 1. Study Area 1, in Castle Shannon, a suburb of Pittsburgh. 6 ^o 0« °r ° W W ° ° 00 ® 000 aved 00 o- *X X < K * O X * X 1=] OOOO vi Figure 2. Study Area 2, in Mount Lebanon, a suburb of Pittsburgh. shrub or he-dgC deciduous tree everorecn tre e scale cy o id NVVdHdOD OOO O« o oo in fe e t 7 T> s- o Figure 3, Study Area 3, in East Lansing* 8 o cv«rgrc-cr> d e c id u o u s trc cr» jj £ T> o 9 R 3 oo ooo R E D CtD/^R fUV£/? 9 Precipitation Temperature Av. Mean Av. Max. Av. Min. Mean Annual Pittsburgh 52.6 61.5 43.6 36.23 East Lansing 46.7 56.1 37.2 31.11 Following are a few general remarks about the weather conditions that prevailed when this study was being made. During the late summer of 1953 and continuing into the fall until late November, abnormal drought and warmth were recorded in much of the country. Throughout eastern United States and into the Midwest the early part of spring in 1954 was particularly warm, followed by abnormally cold and wet weather for a good part of May. Then the summer was hot and dry, followed by an autumn that featured three hurricanes in the northeastern part of the country. last storm in mid-October swept through the Appalachian region. The Otherwise the weather in the Pittsburgh district was favorable, with no heavy snow­ falls or unusual cold spells* The fall of 1954 in southern Michigan was generally mild, with a high rainfall recorded in October. The winter of 1954-55 in the Pittsburgh area was quite cold, with fairly heavy snow on the ground for much of January and a part of February, In contrast, the winter in the Great Lakes region was relatively warm and open. In 1955 and 1956 the weather pattern for western Pennsylvania and southern Michigan was quite similar. March of 1955 was cold while April' and May were marked by periods of warm, dry weather. followed was extremely dry and hot. The summer which According to the East Lansing leather Bureau, July and August were the hottest on record with precipitation much below normal. The summer heat extended into September. reached Pittsburgh and East Lansing in mid-November. Cold weather In Pittsburgh there was a temperature deficit of approximately 100 degrees and a precipitation surplus of about seven inches for the first five months of 1956 (Brooks, 10 1956b:332). Likewise the spring was cold in Michigan, Cool and wet weath­ er was widespread during the summer while the fall was warm and dry. In ■East Lansing September and October were the driest since 1864, and October the warmest since 1920. In 1957 cold weather prevailed until mid-April, and summer presented contrasting weather conditions in western Pennsylvania and southern Michigan. Drought conditions were prevalent in the eastern part of the country while much rain fell in southern Michigan. East Lan­ sing reported the third wettest July in history. Flora The streets within the study areas were quite unlike from the stand­ point of shade trees. None were present along the one street in Area 1; the buildings were adjacent to the sidewalk in most cases (Plate l). In Area 2 there were no shade trees along the streets, but a number of ever­ greens and a few deciduous trees were on the front lawns (Plate 3-A). In contrast to this, the streets in Area 3 were lined with large American elms (Ulmus americana L . K Norway maples (Acer platanoides L.) and silver maples (Acer saccharinum L.) (Plate 4). Only one portion of Area 1 had an appreciable number of shrubs and trees, as is evident in Figure 1 and in Plate 1-B. Spruces (Plcea spp.), pines (Pinus 3pp.), and a great variety of deciduous trees and shrubs were present. In the gully and along the stream, crack willow (Salix fragilis L.) was the commonest species. Lombardy poplars (Populus nigra, var. itallca Muenchh.), apple trees (Pyrus malus L.) and sour cherry trees (Primus cerasus L.) were present in backyards. yard near the northern boundary of the area. Plate 2-A shows one back­ Other than the poplars and willows, there were only two large trees, a sycamore (Plantanus occidentalis L.) and a silver maple, both well over 60 feet in height. Trash was de­ 11 posited constantly in the stream and gully. A hillside on which there was one small grove of trees composed primarily of black cherry (Prunus serotina Ehrh.) rose from a portion of the gully to a busy highway above. Much trash littered the hillside as well. In contrast to the situation in Area 1, Area 2 was composed primarily of well kept lawns. A great variety of trees and shrubs were present, among which were spruces, weeping willow (Salix babylonica L.), lombardy poplar, American elm, American mountain ash (Pyrus americana DC.), white ash (Fraxinus americana L . K ing types. and a variety of ornamentals and fruit-bear­ The hillside marking the southern boundary was planted with Japanese honeysuckle (Lonicera japonica Thunb.), and a row of flowering crab-apple trees (Malus atrosanguinea (Spaeth) Schneid.) stood at the base of the hill (Plate 2-B). (Plate 3-B). Hedges and shrubs often marked the property lines As shown in Figure 2, there were two small woodlots, com­ posed primarily of black cherry. The grounds surrounding one house gave the appearance of a park-like woods. As in Area 2, the lawns of Area 3 were well kept. In addition to the large elms and maples lining the streets, many backyards contained shade trees well over 60 feet in height. Spruces, arborvitae (Thuja occidentalis L.), and many fruiting trees and shrubs were also present (Plate 5-A) . Trees were so common in some spots that a park-like appearance resulted. The woodlots of this area were composed mainly of Norway spruce (Picea abies (L.) Karst.). Austrian pine (Finus nigra Arnold) and black locust (Robinia pseudoacacia L.) were common in the small woods on Cedar Street. In the wooded section near the river there were some oaks (Quercus spp.) and American elms. In the only field (Plate 5-B) the most numerous herbaceous plants were timothy (Phleum pratense L .)t white melilot (Melilotus alba Desr.), Queen Anne’s lace (Daucus carota L.). fleabane 12 (Srlgeron sp.) and common ragweed (Ambrosia artemis11folia L . ) . Fauna In addition to the food provided by trees and shrubs, feeding stations were maintained by some residents. in Areas 2 and 3* One was operated in Area 1 and several Birds and mammals identified in the study areas are listed in Tables 1 and 2 respectively. Transient birds are not included. In Area 1 most of the species were found in about one acre where the feed­ ing station was located and where cover was present. The owner of the property reported that one morning in winter approximately 50 cardinals (Richmondena cardinalis) were in his yard. Since Area 3 was the largest of the study plots and also offered a variety of cover, it was not sur­ prising to find more species of birds here than in the other areas. Frequently robins ignored other species of birds, even when they approached the nest site. On July 5 a hairy woodpecker (Dendrocopus villosus) feeding about 10 feet from nest 54-45 was ignored. On at least one occasion robins retreated before the eastern kingbird (Tyrannus tyrannus), blue jay (Cyanocitta cristata). brovm creeper (Certhia famillaris). starling (Sturnus vulgaris), house sparrow (Passer domesticus), red-eyed vireo (Yireo olivaceus). Baltimore oriole (Icterus galbula) and common grackle (Quiscalus quiscula). It seems that when one bird dominates another, much depends upon which individual acts first. On February 27, 1955, Bernard Van Cleve observed a brovm creeper on a tree trunk which was in the path of roost-bound robins. treated. The creeper charged a robin and the latter re­ On June 14, 1954, I watched a red-eyed vireo pursuing and diving at a male robin, forcing him to the ground. On the other hand, I observed robins driving the rock dove (Columba 13 livia), eastern phoebe (Sayornls phoebe), blue jay, catbird (Dmnetella carolinensis). starling, house sparrow, common grackle, brown-headed cowbird (Molothrus ater), rufous-sided towhee (Pipilo erythrophthalmus)t as well as the eastern chipmunk (Tamias strlatus) and the eastern fox squirrel (Sciurus niger). The house sparrow and common grackle were driven more frequently than any of the others, and seldom were they tolerated near robin nests. Likewise, Common (1947) saw grackles chased by a pair of robins on several occasions. Common, however, and Schantz (1939:168) found that house sparrows were ignored. On the other hand, Arnold (1907:84), Brooks (1939:19), Jensen (1925:591) and Pershing (1930:55) record house sparrows snatching earthworms and/or insects from robins, Richardson (1945:40) and Rohrback (1913:246) found that these weaver finches caused the desertion of two robin nests. While nest 54-6 was under construction, house sparrows removed materials from the nest, even once when the female robin was present. It would seem that both of these species are recognized as predators by most robins, and accordingly they are attacked, as is true of some rodents. Edwin Graff reported that a fox squirrel once climbed to nest 55-23 and just as It reached the nest, one adult robin pounced on it and drove it away. A few days later I observed F3 chasing a fox squirrel vigorously, even though the rodent was some distance from the nest. 14 DISTRIBUTION AND MIGRATION Seasonal Distribution It is a well known fact that the robin is migratory. In neither Michigan nor Pennsylvania is it usually found in appreciable numbers during the winter months. Todd (1940:437) states that this thrush occurs regu­ larly in western Pennsylvania in the winter. In Michigan small numbers are observed every winter in the southern part of the state (Wood, 1951:332). A better concept of the seasonal distribution of this species can be realized if regular visits are made to an area which is utilized as a night roost during the entire year. Such an area occurred in Highland Park, in the eastern part of Pittsburgh, where counts of the robin population were made regularly by Bernard Van Cleve and irregularly by myself from the win­ ter of 1955 to the spring of 1957. These data are presented in Figure 4. It is evident that few robins were found in the winter of 1956-57, and that no appreciable numbers were observed in January, 1955. But the winter season of 1955-56 presented an entirely different story, with a large influx of robins in January. This condition was not peculiar to the roost in Highland Park, nor to the Pittsburgh district as a whole. Robbins (1956:233) commented on the unusual numbers of robins reported in the northeastern United States during the winter of 1955-56. Brooks (1956a:250) mentioned a roost near Huntington, West Virginia, that contained an estimated 5000 robins, and cited a flock of 2300 near State College, Pennsylvania. He also pointed out that an exceptionally heavy crop of wild grapes and of fruits of the flowering dogwood (Cornus florida L.), among others, resulted in a large number of wintering robins. Figure 4* Robins observed at a roost in Highland Park, Pittsburgh, during the winter months from 1955 to 1957. Dots represent dates of observation. 15 a> ro Figure 8. Song cessation of the robin at East Lansing in 1956* 2 Q_ £ v 4-> Q 1 £ s: \ > M ro JULY 4- s: 0 ui owrwe. 0 v AU6 U S T 41 42 heard the last song of the summer on August 7 and August 11 respectively. These last songs are incomplete, brief and feeble in comparison to the songs given during the nesting season. The period of song cessation coincides with the beginning of the post­ nuptial molt. In 1955, in Pittsburgh, I saw the earliest molting robins on June 26 and 28 when at least one tail feather was missing on both in­ dividuals. By mid-July molting robins were quite common. On July 14, I observed several with missing rectrices in East Lansing, and on July 24, I notdd that the rectrices of F4 in Area 1 were very worn, with at least two missing. In August I found molting individuals every day. Resumption of Song in the Autumn After the cessation of song in the summer, singing is often resumed in the fall. Bicknell (1884:127) noticed a secondary song period in the last days of September or in October. song later than November 8. In two years he heard no robin in From data collected over a period of 30 years, chiefly in southern Connecticut, Saunders (1948b:376) writes that he heard this species singing in the fall in 19 different years. The average dates of this secondary song period were from September 28 to October 17; the earliest was on September 13, 1930, and the latest on November 6, 1946. Stover (1912:171) observed that the singing of robins of the year began early in September, reaching its height in the fall. My earliest record of an immature robin in song was on August 19, 1955, at the roost in Highland Park in Pittsburgh, and the earliest record of an adult renewing song was on September 3, 1955, also in Pittsburgh. Another early one was on September 7, 1953, when one song was given in a woodlot near Area 1. From September 15 through October 8, 1957, robins sang practically every morning at approximately 6:30 A.M.. Many of these 43 vocal efforts v/ere incomplete and feeble. Following is a listing of the earliest and last songs recorded in the Pittsburgh area. In 1956 no fall singing was noted in East Lansing. Year Earliest Fall Song Last Fall Song 1953 September 7 November 10 (E. H. McClelland) 1954 October 14 October 14 1955 September 3 October 9 1957 September 15 October 8 Another late song was heard by Dorothy Auerswald on November 12, 1953, near Ligonier, Pennsylvania. With some resumption of song in September and October, it is not surprising to find that the molt is largely completed by this time. All robins observed on October 1, 1955, had apparently fin­ ished the molt. Songs have also been recorded during the winter months by other workers. Black (1932:16) writes that there was considerable singing at a winter roost in Arkansas, which he had under study from October 22 to Decem­ ber 16, 1928. On several occasions Wright (1902:198) heard songs given by robins in a flock on January 7 and 8, 1902, near Cambridge, Massachusetts. 44 CALL NOTES The common call notes of the robin are listed in Table 6 with the conditions under which they were recorded. However, one call note may vary in volume, in pitch, and in rate during a time interval, depending upon the stimulus which prompted the call. If call notes are to be described, words and syllables must be used, and it is not surprising to find different interpretations for the same call note in the literature. In considering the call notes I have listed first the term which I think best represents the call • I recorded the "yeep" call (Saunders, 1951:136) more frequently than any other. This is the "chirp" of Howell (1942:544) and the "pleent" or "plint" of Bent (1949:36). Howell writes that when this call is given loudly, it functions as an alarm note. I observed this many times, but it may be given under a great variety of conditions, ’ //hen young were taken from nests for banding and/or weighing, this call was always given by the adults. Once at nest 56-4 and several times at nest 54-44 it was noted that the "yeeps" stopped for a few minutes after I left the nesting terri­ tory with the young. When I reappeared, the calls were resumed, and when the young robins were removed from a container for transfer back to the nest, the call notes increased in volume as well as becoming higher in pitch. The 55-23 nestlings responded to "yeep" calls given by the parent birds by crouching into the nest. In another case a young robin that had left the nest became motionless when the calls were given. A count of the "yeeps" was made at nest 57-16 on June 7 when I alarm­ ed the female by examining the young. During one minute 69 call notes were 45 given, and 53 in another. Howell (1942:545) counted "yeep” calls given by a female which had young out of the nest. number of call notes ranged from 49 to 56. In five one-minute counts the These are in contrast to a count that I made on a robin feeding with a flock in a wooded area on August 5, 1953, when 21 calls were given in one minute. While sitting on nest 57-13 the male gave no reaction to a tape record­ ing of "yeep” calls. However, when the female returned, he left, giving loud "yeep” calls. At dusk the robin frequently gives ”yeep" calls interspersed with songs and other call notes, among which is the laughing call. It has been de­ scribed as "ha-ha-he-hi-hi-ha-ha" by Saunders (1951:136), "he-he-he-he-he" by Bent (1949:36), and as "chir" or "chee" repeated from 5 to 10 times by Howell (1942:545), who adds that the call is given under a number of con­ ditions but that it may be associated with sociability or a sense of well­ being. The laughing call may be given when danger is near or when one robin intrudes into another's territory. In one instance parent birds gave this call when I approached the nest, and immediately the young crouched low, responding in the same manner as thej' had to "yeep” calls. During two ter­ ritorial disputes the resident bird gave the laughing call when it first noted the intruder, which answered with the same call. notes were more commonly used as an alarm call. However, the "yeep" On March 28, 19 54, the laughing call and the "skeet-urp" call were given antiphonally between two robins for a three-minute interval on the edge of a golf course. Perhaps these calls indicated sociability or a sens© of well-being. In the spring some laughing calls were much reduced in volume and soft in tone. I heard this version of the call when a pair was searching for a 46 nest site, from the male when the female was incubating nearby, and when members of a pair separated from or joined each other. It appeared to serve as a threat also, since it was given on two occasions by the resident bird when an intruder appeared, and once by a female when she found a dummy robin at a bird bath. The "huhn or rttut,f of Bent (1949:56) was also given under a variety of conditions. When a robin was alarmed, the call was similar to sobbing* Two times the 55-23 young crouched in the nest when the parents gave this call. A combination of this call note and the nyeep" note was often given, resulting in "yaePi huh-huh-huh"• On the evening of September 9, 1953, a robin gave this call as it flew from a tree on the edge of a communal feed­ ing area in the direction of a night roost. this individual. Four others then left with That evening the call was heard several times in the sur­ rounding trees as robins flew to the roost. T1Skeet, skeet" is another call listed by Bent (1949:36). This is the one which I interpret as Hskeet-urp", a very shrill call which seems to be given at times of intense activity. In addition to the call notes in Table 6 a few others were heard. Saunders (1951:136) lists a "eeeee" call similar to that of the cedar waxwing (Bombycilla cedrorum). from robins in flight. I recorded this call five times, in every case I heard a call not unlike the bubbling song of the brown-headed cowbird on five occasions, all at dusk, when robins were fly­ ing or were about to leave for a night roost. Perhaps this is indicative of the ability of the robin to mimic the song of another species. Howell (1942:545) writes of a female robin giving a hysterical squeal when she was captured on the nest. I heard similar calls from a young rob­ in when it was taken from a trap for banding, and from a parent when a 4? fledgling was caught for banding. On September 30, 1954, in a wooded part of Area 2, a robin gave an almost hysterical scream whan it was forced to the ground during a chase. 48 POPULATIONS In Wooded Areas From the data on robin populations in Table 7, it is evident that few robins are found in forested areas. Hering (1948:54) covered 75 acres of the Black Forest in central Colorado, which was composed of a nearly pure stand of western yellow pine (Pinus ponderosa Laws.); of the nine nests found, five were on the edge of an open area. In a census of two 20-acre tracts in Latah County, Idaho, where the dominant species of the climax forest Is Douglas fir (Pseudotsuga taxifolia (Poir.) Britt.), Johnston (1949:142) found no robins in the tract that had been selectively lumbered five years before and only 2.5 pairs per 100 acres in a comparatively open tract that had been logged quite heavily in the two years preceding the census. From studies in forested areas, Kendeigh (1944:96) listed the robin as a forest-edge species that may nest in the woods if open sites are nearby. In another study Kendeigh (1948) found the robin as a breeding species in several forest communities of northern Lower Michigan. In July, 1952, when I was a student at the University of Michigan Biological Station, I made a census of the birds in a 50-acre aspen-oak-pine forest located in the same area where Kendeigh conducted his Michigan studies (Mehner, 1952). Some red maple (Acer rubrum L.) and paper-birch (Betula papyrifera Marsh.) were also present. The breeding population consisted of six pairs, of which four maintained territories on the forest edge. In his studies of the avifauna in Crater Lake National Park, Farner (1952:104) found the robin associated with all kinds of forests. He noted, 49 however, that soft, moist soil must be accessible for feeding, as well as a supply of mud for nest-building. From mid-April to mid-May in 1954, I made five censuses of a 10-acre woodlot adjoining the Mount Lebanon Municipal Golf Course in Pittsburgh. Crataegus and black cherry were the commonest species of trees, and there were a few oaks and maples. Six active nests were found, and two other pairs were present, making a total of eight pairs. Much of the feeding was apparently done on the golf course. In Open Areas Soft-bodied insects and earthworms are important items in the diet of the robin; hence, moist soil and open areas seem to be prime requirements. Storer (1926:265) writes that the former range of the robin in California included only those parts where damp, short-grass meadows persisted during the summer months. Formerly none was present in the Golden Gate Park, but after moisture was brought to the area by man, the robin appeared. It is not surprising to find a high density of robins in parks, cem­ eteries, and suburban areas. Young (1949a:1955) found very high popula­ tions (12-19 pairs) in a 5.2-acre tract in the University of Wisconsin Arboretum where Thuja furnished nesting cover. Weeks (1935:137) located 11 pairs in a 4.5-acre residential area that was somewhat similar to Area 3 of this study in that the streets of both areas were lined with elms and maples. He made an effort to attract robins by erecting shallow, box-like platforms covered with two-pitched roofs. Of the 11 nests, 5 were in these shelters. The populations that I found in Study Areas 1, 2 and 3 are listed in Table 7; some are shown in Figures 9-13. In some small sectors of Areas 1 Figure 9. and May, 1956. The breeding population (five pairs) of Area 1 in April Nest 56-2 is outside of the boundaries of Area 1. 50 <3 < l '5 0" o scale c -*t-» o L tU +* V) U w -*u r C <3 64 ible in size or shape* Nevertheless, it is useful to have some idea of the area over which a bird carries out its daily activities. Odum and Kuenzler (1955:129) distinguish between maximum and utilized territory. The former includes the area over which the bird ranges while the latter is only that portion that contains the singing perches, the nesting site and feeding sites. maximum territory. In three cases I was able to determine The members of a pair, especially the male, were ob­ served continuously from three to five hours, and their locations were plotted at approximately five-minute intervals on a map. After every 10 observations the outermost points were connected with straight lines so as to include all of the other plotted points, and the areas were measured with a planimeter. In the case of the 56-24 pair when the young were being fed (Figure 18), and of the 57-15 pair (Figure 19) during incubation, it is evident that a point was reached when there was little or no increase in area. Insufficient observations were made at nest 56-24 during incuba­ tion (Figure 17), and hence there was no levelling-off point when the num­ bers of observations and the resulting areas were plotted. Odum and Kuenzler (1955:153) found that from 25 to 90 observations, or two to eight hours in the field, depending upon the species, were necessary to reach a point beyond which each 10 observations would result in less than a 10 per cent increase in territory size. The above technique was not followed in determining the size of the other territories listed in Table 8 in that the positions of pairs or mem­ bers of a pair were not plotted at regularly spaced intervals. outermost points were connected by straight lines. Again the When less than 20 records were taken for a male or a pair, I did not measure the area. All territories, whether measured or not, are shown in Figures 9-13 so that the Figure 17. Territory of the 56-24 pair in Area 3 during incubation. The numerals represent the increase of area after a series of 10 obser­ vations. 65 p XI VI C 0 a* 3 * < M it 0 04 ro Figure 18* Territory of the 56-24 pair in Area 3 during the period when young were being fed in the nest. The numerals represent the increase of area after each series of 10 observations* 66 o K> O sJ 68 populations of nesting pairs and overlapping can be seen* Other data are available from the literature on the size of robin territories* In Ithaca, New York, Butts (1927:347) observed that the mem­ bers of a pair obtained most of their food within an area of about *50 acres* In a study of a pair raising three broods, Shantz (1939:167) de­ termined the extent of the territory at approximately *80 acres. Young (1951:20) found the average size In the University of Wisconsin Arboretum to be *30 acres, with a minimum of *11 acres and a maximum of about .60 acres* Weeks (1935:137) writes that the average extent in a residential area at Sanbornton, New Hampshire, was *40 acres* Howell (1942:531) gives .28 acres as the average extent in an area where the robin population was high, and .51 acres where it was low* Both Howell and Weeks determined the average size by dividing the area of the plot by the number of nesting pairs. This method leaves much to be desired in view of the fact that territories do vary in size and that many overlap. The largest territories that I measured, about 2.5 acres, were in Area 3, which had the lowest populations. These are maximum territories; per­ haps the smaller ones that I determined in Areas 1 and 2 were utilized territories. Seven of these were in areas where the density was 100 pairs per 100 acres. .60 acres. The range was from .44 to .70 acres, with an average of When the density was 120 pairs per 100 acres, the range of five was from .24 to .87 acres, with an average of .50 acres. The smallest territories were recorded by Young (1951:20), and his study area contained the heaviest populations of robins. This strongly suggests a relationship between density and extent of territory. 69 NESTS AND NEST BUILDING Span of Nesting Season Howell (1942:545-547) summarizes data on nesting dates from various localities in North America, Wood (1951:330) writes that in Michigan nesting occurs chiefly in May, June and early July, Burleigh (1923:147) gives the earliest record for Allegheny County, Pennsylvania, as April 14, 1912, when a nest with four slightly incubated eggs was found. An earlier recent record is April 11, 1956, when a nest with two freshly deposited eggs was collected by a high school student near Area 1. From 1954 through 1956, in Areas 1 and 2, a peak of nesting activity was found in late April and early May (Figures 20, 21), In 1957 two peaks of activity, one in late April and early May and another in late May and early June, were noted in Area 3 (Figure 22), With the exception of 1955, my absences from Pittsburgh in late spring and summer prevented gathering data on late nesting there. The populations given for the study areas are higher than the nest count because all of the nests were not found, Burleighrs (1929:120) latest record is August 18, 1927, when three half-grown young were found near Harmarville, Pennsylvania. The latest nesting that I observed in Pittsburgh was on August 7, when food was still being carried to the young of nest 55-22. Nickell (1957:95) reports three 13-day-old young in a nest on August 5, 1955, in Oakland County, Michigan. On August 3, 1954, I found three dead young, about five days old, on a sidewalk in East Lansing. August 3. The two young of nest 56-24 in Area 3 left on On September 1 and 2, 1956, I observed a fledgling being fed by parent birds in Lansing. Forbush (1929:413) gives a still later record at Figure 20* Robin nesting cycle in Area !• 70 C o Z> o 0 L w C 0/ 1 L ft) CP c C7> V o C D w 4J v> V 7UNJ£ c a-IAV cn U) U) 0) if) 0) APRIL 2 1956 M T a i i i t «M « I I I I TN I I <3 I I I i I t t Figure 21* Robin nesting cycle in Area 2, 71 2 - II <4 ie /MAY A P R tl- 19^4 n fS tS 4 - nes ts n e tt 4 - I - t A4AY to A P R tt. 8 8 22 19SS - 6 - 4 - under 0 8 27 A4AY APft.lt. ) Q S'S JUNE s w itK C o n s tru c tio n Figure 22* Robin nesting cycle in Area 3 in 1957* 72 2 o h v 0 et 0 r>0 J o r»> CM O' c5 <1 Figure 25. Nesting sites of F4 (nests 56-3 and 56-21) and F6 {55-22 and 56-13) in Area 1 in 1955 and 1956, fir s t r> e s t 79 *5--v» fj o 80 Later in the nesting cycle, the attachment to the site is quite strong* Julian Myers of Pittsburgh reported that an occupant in an apart­ ment building pushed a nest from a window ledge* eggs on the ledge. The female then laid two When the nest was replaced on the ledge and the eggs introduced into it, the female resumed incubation* On May 3 nest 55-2 with eggs was transferred from one second-floor window ledge to another, about 15 feet distant, because the house was being painted. However, the female returned to the freshly painted ledge and squatted in the paint even though she had been present when the nest was moved. It was then placed in a metal pan and returned to the first ledge, but not to the original spot. The female still returned to the original site and did not incubate the eggs until the nest was placed there. I moved nest 54-2 with young about six feet to a trap to capture the adults. The female flew to the nest site, however, and assumed an incubating pos­ ture. On May 21 the one young was taken from nest 56-4 for banding, after which the female returned to the empty nest and sat on It. Charles (1909: 30) and Scott (1902:70) noted robins sitting in empty nests. The nest site may continue to exert a strong influence on the adults after the young leave. On May 10 the young of nest 54-8 were frightened from the nest while the adults were nearby. I collected the nest, and after I left the vicinity, the adults went directly to the spot where the nest had been located even though they had seen the young leave. Common (1933:413) observed a female going to a nest after the young had left. Wallace (1939:356) made a similar observation at a Bicknell’s thrush (Hylocichla minima bicknelli) nest. Nesting Height Nests may range from ground level to a height of 60 feet or more. 81 Several observers report ground nests. Rowell (1942:549), at the other extreme, recorded one that was 65 feet in height. I measured or estimated the height of 131 nests (Table 11)• The aver­ age height of 83 in Pittsburgh was 14.5 feet, with extremes of 5 inches and 50 feet; the average of 48 in Lansing and East Lansing was 20.3 feet, with extremes of 4.2 feet and 50 feet. height was 21.2 feet. For 20 nests in Area 1 the average The average of 29 in Area 2 was 12.5 feet, and that of 23 in Area 3 was 23.5 feet. Klimstra and Stieglitz (1957:334) found 10.7 feet as the average height in residential and rural areas in Iowa, and 15.4 feet within the city limits of Carbondale, Illinois. Young (1955: 336) found that the average height was 7.4 feet in Madison, with many of the nests in the University of Wisconsin Arboretum. From a study of 185 robin nests on his undisturbed laboratory grounds near Butler, Pennsylvania, Preston (1946:90) found 7.3 feet to be the aver­ age nesting height. Preston and Norris (1947:262) postulate that low-nest- ing species have been more or less eliminated from suburban areas because of "attrition-pressure" which operates rigorously at the ground level but which declines with height. They further postulate that within a species different individuals have preferred nesting heights. Thus, by "attrition- pressure", certain clans comprising the species have been selected for survival in accordance with their nesting behavior. It is evident that the average nesting height that I found in suburban areas and which Klimstra and Stieglitz found in Carbondale is much greater than that found in rela­ tively undisturbed habitats. The nesting heights of known females are given in Table 12. Since their mates may have been influential in selecting the site, the male, if known, is also listed. With the exception of F3 in 1955, the second nest 82 was placed higher than the first. feot • In 1954 F7 and F8 started nests at 7 F7 then constructed another nest (54-6) 25 feet above the ground and F8 built her nest (54-7) at 40 feet. height for a given female is apparent. From my data no favorite nesting Brackbill (1947c:116) found no preferred nesting height for two females, but a third one built three nests 8.5 feet above the ground. Nest Construction In the early spring, before nest construction is underway, female robins pick up grasses and other materials, and then drop them. undoubtedly influences the start of nest building. Temperature The number of nests in their first day of construction in and around the study areas, together with the average temperature, is shown in Figures 26, 27 and 28 for 1954, 1956 and 1957 respectively. In all three years, the very first nests were started after a rise in temperature. The stimulating effect of high tem­ peratures and the depressing effect of low ones are evident in 1956. Construction is done mainly by the female. First a bulky foundation is built; next a mud cup is added and then the lining, Herrick (1911) describes the behavior-of the nest-building female in some detail. Of 56 excursions to gather nesting material ,ytiat I recorded in my field notes, the male accompanied the female 17 times. At other times the male was usually nearby, on a perch or feeding on a lawn. Herrick (1911:547-348), Jordan (1901:108), Kelly (1913:310) and Samson (1923:106) write of males bringing material to the nesting site. Once while nest 54-6 was under construction I observed the male crouched in the nest, turning about as if shaping the cavity, an action also de­ scribed by Shantz (1939:158). A variety of materials was used in nest construction. Analyses of Figure 26. Nests in their first day of construction in and around Areas 1 and 2 in 1954. 83 i) * OJ -£> s D R? > li. o APRIL. 3 +-» 5 QJ cu £ £ o> s: aJ O' D h < Cv UJ CL I 0} h ^45 00 i 1 ( i O r" C3 £> i sJ- / i o Figure 27. Nests in their first day of construction in and around Areas 1 and 2 in 1956. 84 CO r <*> IL ~“n M d V OJ D t < o' Ui X UJ o -J5 o *o o Figure 28. Nests in their first day of construction in and around Area 3 in 1957• 85 0 V D -M qJ £ a) „ ~o k *0 UJ o o o *o o CO APRIL _ r* 86 nests collected in Pittsburgh and East Lansing are given in Table 13. Grass was found in all of them. composed entirely of grass. of 17 foundations. Of the 12 nest linings examined, 6 were Roots were found in 2 linings and in 14 out Several times when I was observing robins gathering grass, I noted that they pulled up the roots as well. Seven of the eight foundations with bark had pieces of grapevine bark. I saw one female collecting this in Area 1. Once she grasped a loose piece in her bill, then fluttered into the air, pulling at it. attempts she got a small piece. After three Another time she tried unsuccessfully to get bark by pulling at loose pieces from a perch b8low. I found numerous twigs in the nests analyzed; the longest, about one foot in length, was from an American larch (Larix larlcina (DuRoi) K. Koch). Pearson (1910: 207) reports a nest containing 63 slender Abies twigs, some of which were one foot in length. I watched the unsuccessful attempts of the above mentioned female trying to collect twigs from a silver maple. She grasped a twig with her beak, then pulled at it as she walked along a branch below. However, she was able to break off twigs from a grapevine. Paper, cloth and cord are commonly found in robin nests. Of 17 nests examined, 9 had white or brown cord, the pieces ranging in length from 3 to 36 inches. While gathering material for nest 55-14, El succeeded in removing some stakes and string marking rows where seeds had been planted, but evidently she found the material too bulky to incorporate into the nest. Frequently paper and/or pieces of cloth are deposited first in the crotch. Hanging from the base of nest 55-24 was a piece of cloth about two feet long and two inches wide. Another nest contained a piece about six feet in length and one-third inch in width. Seven nests that I ana­ lyzed contained paper, the largest a cleansing tissue. Materials other than mud may be used for the cup that is added to the 87 foundation* When Fll was gathering material for the cup of nest 57-22, she took muck and decayed vegetation from a bird bath. writes that the nest sometimes lacks a cup. Nests show some variation in size and weight. Forbush (1929:411) The nesting crotchor site influences the size of the nest, and the amount and type of materials determine the weight. Nickell (1944:54) found that nests with a clay cup showed a greater average 7/eight than those with a cup of sandy muck and that nests with muck weighed least. Linear measurements based upon 17 col­ lected nests, and dry weights based upon 19 nests, are given in Table 14. Nests were oval in shape, and I measured the long diameter or long axis as well as the short diameter or short axis. I studied one female while she was constructing the outside shell of nest 54-6 on April 15 and v/hen she was adding lining to iton April 16,as well as during an unsuccessful nesting attempt on April 11(Figure 29). The average time she spent at the site on April 11 was 1.4 minutes while the average interval away from the nest was 6.0 minutes; on April 15 it was 2.8 and 3.3 minutes, and on April 16 it was 5.6 and 15.0 minutes. During the observations on April 11 there was a drizzle of rain, and on April 16 there was a hard shower. These conditions may have cut down the activity. However, a female carried material to nest 57-16 on Kay 18 during a very heavy rain. In the case of nest 54-6, the intervals at the nest and away from it were longer when the lining was being added than earlier in the construction. Even though the nest appeared complete on April 16, she car­ ried grass to it on April 19. Herrick (1911:347) noted that a female re­ mained at her nest for longer and longer intervals during the third day. Kelly (1913:310) observed a nest that was completed in one day; Shantz (1944:118) reported one v/hose construction extended over 18 days. Figure 29. Nest-building activities of the 54-6 female in Area 1. 88 o r o» o „ o tsi 89 How© (1898.164) writes that the variation in time is caused by weather conditions and by whether or not the female is ready to lay her eggs. found thnt the average time needed for seven nests was six days. (1949a:40) found it to be seven days. 12 nests was four and one-half days. He Young In my study the average time for Nine of them were first nests, and the average time was four days, with extremes of two and eight days. Two of those nests, 57-1 and 57-3, were built in two days, following a very pronounced change from cold to warm weather. The average time for the three later nests was 5.7 days, with extremes of two and eight days. Four of the 12 were constructed by FI. Her first nests, 54-2 and 55-1, required four and one-half, and five days respectively, and her sec­ ond nests, 54-30 and 55-14, eight and seven days respectively. In both years these second nests were constructed in late May and early June when she was helping care for the first broods that were out of the nest. How­ ever, Howell (1942:589) found that the time for building second nests aver­ aged about four days while that for first nests averaged about six days. Multiple nests, either of the storied type or side by side on a hori­ zontal surface, have been found by several observers. a robin nest being used for more than one brood. her first broods in 1954 and 1955. Many authors record F3 used the same nest for F I ’s first nest in 1956 was constructed in 19 55 by an unmarked female. Arthropod Fauna of Robin Nests In 1954 I found a number of blow-fly larvae in three nests. These specimens, and later others, were sent to the Insect Identification and Parasite Introduction Section of the United States Department of Agricul­ ture, where D r . C . W. Sabrosky, in collaboration with Dr. S. Bennett, 90 placed them in a new species of Protocalliphora. which will be published in. the near future (personal communication). Johnson (1925:53; 1927:2; 1929:29; 1932:26), Mason (1936:113), and Plath (1919c:375-376) report the occurrence of the blow-flies, Calliphoridae, in robin nests. Johnson (1925:53) writes that the larvae usually hide in the nest during the day and that at night they emerge to suck blood from the nestlings. Plath (1919a:193) introduced larvae of Protocalliphora azurea (Fallen) into a cage containing lesser goldfinch (Spinus psaltria) nestlings. Later larvae were found on the feet and low­ er parts of the body of each nestling. Thomas (1936:46) postulates that the larvae normally leave the nest at maturity and pupate in the ground unless a mud cup or a nesting cavity prevents them. In the Puget Sound region, Plath (1919c:374) found 18 out of 25 (72 per cent) robin nests infested with Protocalliphora azurea. number of larvae ranging from 7 to 138 per nest. He found the I found Protocalliphora in 8 out of 20 (40 per cent) nests taken in Pittsburgh (Table 15), but none in the six nests collected in East Lansing. All were of an undescribed species, with the exception of three P. metallica Tns. in nest 56-1. adults than puparia are listed for nests 54-8 and 56-8. More Evidently some of the pupal cases were lost when the nests were taken from gallon iars In which they were stored. were found. In the other six nests more puparia than adults It is possible that some of the pupae were parasitized and thus did not complete their metamorphosis. Mason (1936:113) and Whitehead (1933:293) found chalcid-flies, Chalcidoidea, parasitizing Protocalliphora. Two of the nests listed in Table 15 were collected by students who did not record the height, but the others were low. Plath (1919c:375) be­ lieves that the height of the nest may be a factor in parasitism by 91 Protocalliphora. George and Mitchell (1948:550), Mason (1936:113), Neff (1945:75) and Plath (1919a:199; 1919b:38) attribute deaths of nestling birds to blow-fly larvae • Of the eight nests listed in Table 15, five were known to be suc­ cessful in producing apparently healthy young. Johnson (1927:1; 1932:28), Thomas (1936:46) and Sargent (1938:83) likewise observed no ill effects upon several species of nestling birds. I found the following specimens of arthropods in robin nests. Number Nest Crustacea sow-bug, Porcellio laevis Koch 2 54-40 32 54-43 2 56-1 1 54-50 16 54-40 Insecta Phalaenidae (puparium) Anthomyia pluvialis (L . ) Fannia sp. Bradysia sp* 1 27 56-8 54-43 Arachnids Ornithonyssus sylviarum (C . & F . ) 54-43 Of these, the northern fowl mite (Ornithonyssus svlviaruin) is the only parasite; it breeds directly on the host (Ewing, 1929:12). Peters (1936:21) lists the following ectoparasites of the robin: several species of bird lice (Mallophaga), two species of louse-flies (Hippoboscidae), as well as several mites and ticks. 92 EGGS Description The eggs of the robin are greenish-blue in color. In Pittsburgh the average size of 17 eggs in millimeters was 29.2 x 20.3 and in East Lansing 7 eggs averaged 29.2 x 21.5. The maximum length in Pittsburgh and East Lansing was 31.0 (two records, x 19.9 and x 20.1) and 30.9 (x 21.2) re­ spectively, and the minimum length was 27.1 (x 20.0) and 27.1 (x 21.3). The maximum width was 22.0 (x 29.5) and 22.0 (x 30.0), and the minimum width was 19.5 (two records, x 28.9 and x 29.0) and 21.2 (two records, x 28.9 and x 30.9). For 30 eggs in the Ithaca region Howell (1942:562-563) found that the average length was 28.4 and the average width 20.7. termined the average weight of 60 eggs as 6.26 grams. He de­ Hamilton’s (1935: 109) observations indicate that during incubation there is a loss of more than 25 per cent of the original weight. Oviposition For seven nests, six in Pittsburgh and one in East Lansing, I found that the average time between the completion of the nest and the appearance of the first egg was four days, with extremes of two and seven days. Young (1955:336) observed that oviposition usually began three or four days after the nest was completed, but that there may be no interval or as much as 15 days elapsing before the first egg is laid. Eggs are usually deposited at the rate of one per day until the clutch is complete, although Young (1955:337) found it common for the female to skip a day. 93 Clutch Size Young (1955:337) calculated the mean clutch size for 273 nests as 3.4 ± .05. The mean clutch size for 42 nests in Pittsburgh was 3.4 - «H ; for 13 nests in East Lansing it was 3.5 eggs or more are uncommon, i .18 (Table 16). Sets of five Howell (1942:536-537, 561) discusses large clutches, citing examples of six, seven and eight, some of which are known to represent the laying of two females. Using the Maryland data on file at the Patuxent Research Refuge and data gathered by Howell at Ithaca, New York, Davis (1955:21) calculated the mean monthly clutch size, and these data are comparedwith mine in Table 17. in clutch size in June, but no In all cases there is a drop trend is evident in the early spring. Incubation The female robin may begin to sit on the eggs before the clutch is complete. However, the presence of a bird on the nest does not imply that full heat is being applied to the eggs. I found the female of nest 57-18 on the nest in the afternoon of the first day of egg laying. On the second day of oviposition, the female of nest 55-23 was incubating in the evening while the females of nests 57-7 and 57-9 were incubating earlier in the day. not attentive to her eggs until the The female of nest 54-45was third day. In the case of two nests Kendeigh (1952:127) noted that the female was on the nest the night after the first egg was deposited. Herrick (1911:349) observed that incubation began at one nest on the second day of oviposition, and for three nests Schantz (1939:159) found that incubation began on the evening of the second day. In the studies of single nests, Charles (1909:27) and Murray (1930:428) found the start of incubation to 94 be the third day while Saunders (1938:81) did not observe the female in­ cubating until the day after the third egg was laid. I determined the incubation period for 12 nests, 10 in Pittsburgh and 2 in East Lansing, by recording the day the last egg was laid and the day it hatched. Seven clutches were incubated for 12 days, four for 13 days and one for 14 days, with a mean period of 12.5 * .19 days. This is in agreement with Kendeigh*s data (1952:127) which indicated a mean interval of 12.4 days for 13 nests and with YoungTs (1955:337) which gave the mean length of incubation as 12.5 * .14 for 57 eggs. Koehler and Koehler (1945: 17) record a female which sat on three eggs for 19 days, then abandoned them. Periods of attentiveness and inattentiveness have been studied at two nests by Schantz (1939), who used an electrical apparatus to announce and/ or record the arrivals of the parent birds, and at four nests by Kendeigh (1952), who obtained data with thermocouple and potentiometer. Forty at­ tentive periods taken at random by Schantz (1939:160) during the incubation of a second clutch after the first two days averaged 44.2 minutes, alter­ nating with inattentive periods of 11.3 minutes. cent of the daytime was spent on the nest. Thus approximately 80 per At a later nest Schantz (1944: 118) recorded 32 attentive periods that averaged 20.6 minutes and inatten­ tive ones that averaged 5.6 minutes. Kendeigh (1952:128) found that early in the spring the percentage of daytime spent on the eggs was between 78.7 and 76.2, while in June and July it was between 67.0 and 68.6, with the decrease attributed to rising air temperature. I determined several periods of attentive and inattentive behavior at eight nests (Table 18). Twenty-one periods of attentiveness averaged 36.4 minutes, while 23 intervals of inattentiveness averaged 6.3 minutes. While 95 I was watching nest 54-45 on July 3, there were periods of hard rain when the female remained on the eggs. On May 2 the female incubated nest 54-6 during a thunderstorm in the late afternoon. During a light drizzle of rain on May 3 she was huddled in the nest with her bill almost flush with the rim. "For 13 attentive periods, I noted that the incubating bird changed her position on the average of once every 14.4 minutes. However, Herrick (1911:350) observed an incubating female which maintained one position with little deviation. In the course of 14 hours, Schantz (1944:118) found that a female changed position 70 times. Sometimes when the female changed hsr position she probed the nest with her bill, with an average of once every 18.9 minutes for eight attentive periods. I was unable to see what she was doing, but it is quite possible that she was turning the eggs. Schantz (1944:118) writes that the above mentioned female turned the eggs 22 times in 14 hours. In nest 57-7, a cracked egg was retained throughout incubation even though it was reduced to a mere shell. In other instances such eggs dis­ appeared from the nest, evidently removed by one of the adults, or else the nest was deserted. Frequently I found the male perched near the incubating female, and on several occasions I saw the male at the nest. Eighteen observations were made at eight nests of one adult relieving another. Six times call notes were given by one of the adults, but in the other cases no notes were used. I noted that some males perched on the nest rim while the female was away. Schantz (1944:110) writes that the male spent 60 minutes at the nest that he studied for 14 hours. I made 11 observations of six males sitting on the eggs while the fe- 96 male was away. For three intervals of 8, 10 and 22 minutes, the male crouched in nest 57-13 like an incubating female. The other attentive periods by the male were brief, ranging from one to three minutes* Brack- bill (1944:139) and Samson (1923:107) record males sitting on the eggs during adverse weather conditions. This behavior cannot be considered true incubation, however, as the male lacks an incubation patch (Bailey, 1952: 127) . Hatching Robin eggs hatch within a period of about 24 hours (Hoxvell, 1942:568), and a clutch tends to hatch over a period of two or three days (Kendeigh, 1952:127). Following hatching, the shells are usually carried from the nest. Shell-carrying is quite general among the Turdidae (Nethersole-Thompson, 1942:191). The remains of an egg from each of two nests, and of two eggs from another nest were carried to points 100, 55 and 75 foet away. In the case of 55-7, however, I collected shell fragments directly under the nest. One half of a shell from nest 54-2 was tucked inside of the other part. This is commonly observed in the song thrush (Turdus ericetorum) (Nethersole -Thompson, 1942:214). The female may eat the shells. female of nest 54-22 did this. Charles Reinbolt reported that the Howell (1942:568) cites a similar observa­ tion • Infertile eggs may be retained in the nest. In nest 57-7 one egg that had been cracked remained in the nest throughout incubation even though it was reduced to a mere shell. The movements of the birds may grind the pieces into the lining, and this may account for some of the shell fragments 97 found in nests. In other instances such fragments may be from shells that were not removed from the nest, or in cases of robbed nests, shell frag­ ments may be left by predators after eating the eggs. 98 THE YOUNG Physical Development The development of Y79 of nest 57-16 is shown in Plates 7-9. Howell (1942:569-581) describes the growth of robin nestlings in detail, includ9 ing the daily changes in weight, total body length and length of wing, tarsus and tail. 54-44 (Figure 30). I recorded the changes in weight for the young of nest The nestling that was missing on July 14 may have died and been removed by one of the adults. carrying off a dead nestling. Judson (1915:213) writes of a male Nestling 512-77931 was one day younger than its two nest mates, and its increase in weight after the fourth day, when it weighed much less than Nestling 512-77932, was very pronounced. Baldwin (1922:222) found that the weight of the youngest member of a brood of three increased similarly; by the ninth day it even surpassed one of its older nest mates. That an age difference of two days or more may be very un­ favorable for the youngest member is indicated by Nickell (1957:95), who found three four-day-old young and another not more than two days old in a nest. Three days later the latter was dead. Attentive Behavior of Adults at the Nest Kendeigh (1952:129) writes that there is no pronounced difference in the amount of attentiveness to eggs and to young nestlings. With an itograph at a nest, he found that the time spent brooding young the second and third days after hatching averaged 36.3 minutes per hour from 8:00 A.M. to 2:00 P.M. and 43.4 minutes per hour in late afternoon. At another nest over a 10-hour period, the average time spent brooding the young was 29 Figure 30. Daily changes in weights of the robins in nest 54-44. 99 h c c tlm q h a tc h e d n«Stlirv«3 30 - n e s tlin g WEI6 HT m is s in g JUL) 14 fi­ ll JU LY DAYS 19 20 S’I Z ‘7 7 9 3 2 JULY tO S’I 2 ' 7 T 9 3 1 100 minutes per hour. Howell (1942:583) states that the female broods her young at night until they leave the nest. On the other hand, Kendeigh (1952:134) states that the female does not sit on the young at night when they are fairly well grown. However, at nest 54-45, when the nestlings were 14 days old and filled the nest completely, I observed the female settling down on them at dusk. Her body merely rested on the nest rim. the male sat on the young for a three-minute interval. The day before, Ghiselin (1956:235) saw a male brooding five-day-old young. From approximately 16 hours of observation at seven robin nests, I found a rather wide variation in the rate of feeding, with an average of 6.4 times per hour (Table 19). In late July, Kendeigh (1952:129) obtained records for five of the last six complete days that young were in a nest and calculated an average of 6.1 feedings per hour. very complete data on two broods. Schantz (1939) gives Over a period of 10 days, a first brood averaged 6.7 feedings per hour, a second one 6.5 feedings per hour. At one nest, Schantz (1939:163) found intensive peaks of feeding activity from 4:00 to 7:00 A.M. and from 9:00 to 10 A.M.. On the other hand, Charles (1909:29) found that the most active feeding time at two nests was late afternoon and oarly evening. Both sexes feed the young. The male of nest 55-23 did not participate in feeding at the beginning or at the end of the nestling period. Likewise, the male of nest 56-24 was not active at the end, but at nest 54-45 the female was not attentive to nestlings about ready to leave the nest. Schantz (1939:164) observed that in three successive broods the male shirked feeding on the day before the young were fledged. An egg introduced into nest 57-7 hatched two days before the others. 101 The adults responded by feeding the nestling. On May 4 a nestling cardinal that had fallen out of its nest was placed in nest 55-2, v/hich contained four robins about the size of the fringillid. On the morning of May 9 it appeared to be in good health, but later in the day it was missing along with one of the robins. By removing food with blunt forceps from three nestlings on alternate days, Hamilton (1935:110) found that approximately two grams of food were brought on each visit. At times I noted that parent birds returned to the nest without food, and evidently in an effort to appease the young placed their empty bills in the gaping mouths. From analyses of 15 stomachs taken from robins ranging in age from 3 to 35 days, Howell (1942:587) found that animal matter made up 70.2 per cent of the food, and plant material 29.8 per cent. My earliest record of vegetable material being brought to nestlings was at nest 57-20, where fruits of the American elm were fed to young be­ tween seven and eight days of age. At nest 55-23, when the young were 11 days old, 2 out of 16 feedings consisted of Amelanchier fruits. Lonicera berries were brought to the young of nests 54-45 and 56-24 when they were 13 and 15 days old respectively. the food. Evidently some grit is introduced with Howell (1942:588) found gravel in robins three to four days old. An examination of a stomach of one of the 57-15 brood that died shortly after fledging yielded sand and grit. After being fed, the young often raises up and passes a fecal sac into the bill of the parent, which eats the material or carries it from the nest. I noted that five fecal sacs were carried approximately 100 feet from nest sites, and another 150 feet. In the late stages of nesting, the young evacuate over the nest rim, and these excreta may also be eaten. During 102 approximately four and one-half hours at nests, I made observations on this behavior. These data (Table 20) indicate that waste material is re­ moved about three times per hour, and also that robins eat fecal material in varying degrees. At one nest, Saunders (1938:82) noted that the adults swallowed the excreta until the last two days the young were in the nest, that some nests became soiled at this stage. nounced at nest 54-45, excreta. I observed This was particularly pro­ "Even the leaves below the nest were covered with For two days preceding the departure of the young, both adults, the male in particular, probed the sides of the nest and the surrounding leaves for fecal material. Tyler (1913:397) records similar behavior on the part of a female which perched near the nest and made dives for the fecal sacs as soon as the young voided them. To a lesser extent the female of nest 55-23 exhibited such behavior on the day the young fledged. Once in the morning she took a fecal sac, flew to a nearby tree and ate it. She ate another that had been voided on the plank where the nest was placed, and once she ate excreta on the outside of the nest. probed into the nest, perhaps taking fecal material. the nest when I examined it later in the day. Twice she Some was present in This may be an important factor in nest probing observed in adults caring for young. However, Protocalliphora puparia were present, and perhaps she was eating them. Haverschmidt (1953:249) associates nest probing with removal of parasites and/or food remnants. The concern of adults for nestlings varies somewhat from nest to nest, but it appears to increase with the development of the young. When nestlings were taken for banding, the adults frequently dived at and sometimes struck me, but they usually quieted down after I left with the young. When I re­ 103 turned, protesting call notes were given, but not until I removed young from the small box used for transporting them did the parent birds show a marked reaction. Extent of the Nestling Period The listing below gives the extent of the nestling period for 37 individuals. Days in Nest After Hatching Number of Young Pittsburgh East Lansing Total 12 0 2 2 13 10 2 12 14 9 2 11 15 4 6 10 16 0 2 2 The mean number of days spent in the nests was 13.9 * .16. This is somewhat higher than the 13.4 ± .13 days calculated by Young (1955:338) for 89 nestlings. However, he included individuals that were obviously disturbed on their eleventh day in the nest. Howe (1898:167) found that the nestling stage for five broods averaged 14 days. In his study of three consecutive broods, Schantz (1939:166) noted that the second and third broods left 14 days after hatching while the first left after 15 and 16 days. The two young that I recorded for 16 days in nest 57-2 were also members of a first brood, but it is thought that cold, wet weather was an important factor in keeping them in the nest. By the time young had been in the nest for 10 days, they became very active, particularly when the parents came to the nest. stretched and flapped their wings. They stood up, During the afternoon of their twelfth day in the nest, the 55-23 nestlings stretched their wings after each feed­ 104 ing. One even perched on the nost rim briefly. Eleven-day-old young in nest 54-45 preened themselves, and this was observed frequently in other nests as the young developed. ing itself was at 12 days. The earliest record of a nestling scratch­ When the adults were absent, the young slept for short intervals, their heads sometimes resting on the nest rim. On June 26, I watched nest leaving at nest 55-23 in a grape arbor. Y52 was fledged before 8 A.M., and E3 continued to feed the remaining two. After a feeding at 10 A.M., Y53 climbed out of the nest, preened its feath­ ers, was fed again, and returned to the nest within 10 minutes. At 2:30 P.M., Y51 climbed out of the nest, only to return, and for about 20 minutes both young were very quiet. About seven hours after Y52fs departure, Y53 left the nest, at which time Y51 perched on the nest rim. About 30 minutes later, immediately after a feeding, Y51 flew clumsily to the ground, land­ ing about 25 feet from the nest. Seven minutes later, it fluttered down an embankment into a clump of shrubs, a distance of about 35 feet. In one brood that Schantz (1939:166) studied, the oldest individual flew 33 feet to a perfect landing in a tree while the younger two flevt about 20 feet. At nest 54-45 two young left the nest in the morning of July 24, one perching about two feet above the nest until mid-afternoon. A third one remained in the nest until 3 P.M., and for two hours preceding its depar­ ture no food was brought to either one. tree. By evening both had left the nest Some fledglings remain in the nest tree for a day or more, as ob­ served in a robin from nest 54-7, and one from nest 54-44. Charles Rein­ bolt reported that the two young of nest 54-21 in an elm remained there the day they left the nest. Robert Clark observed the three young leaving nest 56-61 at hourly intervals on the morning of May 26, but Schantz (1939:166) watched all 105 three young of a brood leave within a few minutes of each other. However, the members of a brood are not necessarily fledged on the same day. Common (1947:244) recorded one fledging about 40 hours before its two nest mates, and Chiselin (1956:235) observed three fledging over a period of five days, Nice (1944:2) gives an unusual record of the eldest young leav­ ing the nest four days before its three mates. Interval Between Broods Robins frequently raise two broods, and sometimes they are successful in producing three. The average interval between the fledging of a first brood and the completion of a second nest in five cases was 11,4 days; between the fledging of a first brood and a second one it was 41,7 days in three cases (Table 21). I noted that the female usually helps care for the first fledglings up until the second brood is started. However, the time between broods varies considerably. Judson (1915: 213) records a female building the second nest and laying the first egg be­ fore the first brood was fledged. Schantz (1939:158) noted a female se­ lecting her second nest site two days after the first brood left the nest. Ghiselin (1956:235) records an interval of 22 days between the fledging of a first brood and the renovation of the same nest for a second brood, with 49 to 53 days elapsing between the fledging of the two broods. Tyler (1913:395) found an interval of six days between the time the first brood left the nest and when the female began incubation in the same nest. In Area 3, five days elapsed between thedestruction of nest and the completion of the second nest, 57-13. 57-3 Mousely (1917:583) collected three successive clutches from one female and found 10days passing before the completion of another set. 106 Fledgling Period After the young were fledged, they spent the next 10 to 20 days in the vicinity of the nest site. Areas in which three broods confined their activities were determined as follows. Location Nest Number of Records Days Near Nest After Fledging Area in Acres Area 1 55-23 31 15 1.0 Area 3 57-2 50 19 5.8 Area 3 57-11 49 13 2.8 The day that the young of nest 55-23 left their nest, they moved a few feet into a small woodlot to which they largely confined their activ­ ity. However, some individuals moved considerable distances a few days after fledging. Following are some maximum distances at which fledglings were seen from their nests. Young1s (1955:339). The records marked with an asterisk are The two that I found 4000 feet from nest 54-40 were feeding in the same woodlot. Days After Fledging Feet From Nest 0 190 1 225* 2 240* 3 390* 4 555 7 900 14 1275* 28 4800* 31 5400* 41 4000 45 4000 107 Usually the male played the more active role in caring for the young* The female at nest 55-19, a second brood, was not seen after fledging day, and M3 cared for the offspring* At nest 55-23, however, M2 carried food to Y52 for one day, after which he disappeared and was not seen again until the following spring. ity* Sometimes the adults assume equal responsibil­ Schantz (1939:166) writes that two young in a first brood were cared for by the male and the third by the female, while a later brood remained closely associated with both adults. I noted behavior similar to the lat­ ter in the first brood from nest 57-2. The attentive behavior of males in relation to five fledglings is given in Table 22. During approximately two and one-half hours of obser­ vation, the average rate of feeding was 7.8 times per hour. ness of the male continues during periods of rain. The attentive­ On May 19, in a very heavy rain, the bedraggled male of nest 57-11 brought food to young which had left the nest three days previously. On May 25, I flushed Y76 from a spruce thicket during a rain, and it moved to an open perch. When the male returned, he flew at Y76, hitting it with his feet and causing it to re­ treat. It would seem that the male was encouraging the fledgling to take shelter • Sometimes young robins which become separated from their parents are adopted by other adults. Y75 v;as the only survivor of the 57-15 brood, and several times I saw it and an unbanded fledgling being cared for by an un­ marked male. Once I saw Y35 of nest 55-8 being fed by an unbanded male even though its parents were in the immediate area. Nice (1944:2), Schantz (1939:166) and Young (1955:339) report similar examples. In the following tabulation I have divided the fledgling period into three stages; the earliest appearance of certain activities is also given. 108 Days Since Fledging Stage Earliest Observation Activity 1. Hiding 0-3 location note 0 2. Early-flying 4-6 probing in ground 4 3. Semi-dependent 7-20 grasping and pulling at twigs, bark and leaves 5 tail flicking 5 obtaining food 7 cocking head 8 chasing another young 11 singing attempt 14 bathing 15 The Hiding Stage is characterized by the fledglings restricting their activity to trees and shrubs, by periods of little movement, by fre­ quent use of the location note "seech-ook", and by their complete depend­ ence upon the parent birds. On the day of fledging I noted that the majority of young were on the ground for short intervals until they found adequate cover. Instances of young birds remaining in the nesting tree or shrub have already been cited. However, in parts of Area 2, where residents placed bread and other food in their backyards, some fledglings came to the ground with their parents to be fed. Grace Townsend’s obser­ vation near dusk on the day the young left nest 55-1 indicates that the adult birds may aid the young in finding shelter. The female giving call notes was followed by two fledglings into a spruce w£ere they remained, after which she flew to a nearby apple tree with a third one. Once the fledglings found adequate cover, they stood or crouched on a perch for varying periods of time. One remained, almost immobile, on a 109 branch for 75 minutes, and another for almost three hours. perched on a branch Y9 of 54-40 for at least 12hours, six feet from the nest; Y22 of 54-44 remained on a branch two feet below the nest for at least 24 hours. On the day after fledging of Y61 I found it "frozen" in an upright posture for about three minutes. Upon leaving the nest the young give the location note almost contin­ uously. When Y43 left nest 55-19, I counted the call notes given for five consecutive one-minute intervals. 9 and 9, with an average of 9.8. The calls por minute numbered 14, 10, 7, Three days later, in four consecutive intervals, its nest mate, Y44, gave 2, 6, 6 and 1 calls, with an average of 3.8 per minute. The use of "seech-ook" decreased appreciably over the succeeding days. During Stage 1, flying attempts were somewhat clumsy and labored. Five days after fledging, many young were maintaining level flight with ease. es. However, some experienced difficulty in judging the heights of perch­ Seven days after a fledgling of the 55-8 brood left the nest, it attempted to reach a roof about 30 feet high by flying almost straight up when it neared the building. The young robin couldn't reach the roof and then changed its course, flying to a nearby tree. Young that had been fledged eight days or more appeared capable of sustained flight. imum flights that I recorded are given below. Days Since Fledging Length of Flight in Feet 0 40 1 60 3 150 10 800 Some max­ 110 During Stag© 2, fledglings began to move readily from one branch to another, using their wings and tails to balance themselves* They grasped and pulled at twigs, and picked at pieces of loose bark and at leaves. Young flicked their tails when they gave call notes and when they were alarmed, but the tail was not moved with the precision that adults and older young exhibit. Even though considerable time was passed under cover in Stage 2, the fledglings spent more time on the ground than formerly, and they began to probe in the soil and leaf litter. Stage 3 is characterized by a growing independence. Y 76, seven days after fledging, was probing in the leaf litter of a woodlot for undetermined items of food. I have no other observations on independent feeding until 11 days after fledging. Adults often cock their heads before probing, and this activity soon developed in fledglings. Brackbill (1947a:115) found one fledgling taking cherries effectively 10 days after it left the nest, but even 8 to 10 days later it displayed little success with animate food. Even when the young were able to acquire food for themselves, they continued to beg and follow their parents. At times the fledglings and adults moved side by side over the lawns. On June 6, 1957, two unmarked young ran to a male each time he probed in the ground. As the offspring developed, the parents encouraged independent feeding by placing food on the ground and by moving away, thus avoiding the gaping young. Grace Townsend’s observation of El and her 55-1 brood, 11 days after fledging, shows parental influence in teaching fledglings to feed for themselves. By picking up pieces of bread, carrying them a short distance and dropping them on the ground, FI encouraged the brood to follow her. Before the young could reach her, she would eat some bread, pick it up and move away again. Ill The earliest avoiding reaction that I saw was on the seventh day after fledging, when the male of the 56-12 brood jumped over a gaping young and moved over the lawn* Six days later, however, during a very heavy rain of about two hours duration, the male brought food regularly to the young perched on a sheltered window ledge. tempted to avoid them* After the rain the male again at­ Brackbill (1947a:115) records two young being fed by adults 17 days after fledging. Young robins often picked up pieces of leaves, bark, and paper, then shook them and tossed them aside. These playful actions ?;ere also evident after the young became independent. In August, 1954, when I was trapping robins in a woodlot, the young pecked at the draw-string on the trap, often at knots* The earliest antagonistic behavior that I recorded was in the 55-23 brood, which was feeding in leaf litter. which promptly chased it. Y51 came within 12 inches of Y53 Schantz (1939:166) observed a young that was out of its nest 11 days monopolizing a bird bath and driving robins and other species away when they alighted. The first singing attempt noted was from Y16 of nest 54-41 when it gave a series of harsh notes. Mrs. Amelia Laskey reported a robin singing when it was about three weeks old (Nice, 1943:141). Y76 bathing at a bird bath 15 days after it left the nest is the earliest record I have of this behavior. At first it appeared very in­ experienced, only lowering its body partially into the water. On a sec­ ond attempt it bathed for 20 seconds. Even though the location and begging notes are still prominent in Stage 3, other call notes are given. A "yip" note is thought to be the forerunner of the "yeep" note, and it was given when birds were flushed. 112 I heard Y80 of the 57-16 brood give this note 10 days after it left the nest* Y43, from nest 55-19, gave a nasal "yeep, chur-churn call two days after fledging; this is the earliest record of a vocalization resembling an adult call note* On May 31, 1957, I heard an independent young giving nhuh" notes. My final observations of young with their parents near the old nest site ranged from 10 to 20 days after fledging. The mean extent of the fledgling period for 15 broods was 14,9 * .74 days, with first broods leav­ ing their nests on the average of 1.5 days before second ones. However, both 56-12 and 57-2 were first broods, and they remained for 19 and 18 days respectively* Even when the 57-2 female was building her second nest, the young were tolerated, but she did not feed them# The last day that I ob­ served the young from nest 56-12, the male pounced on one and drove it from the area. Brackbill (1947a:115) found two fledglings in the nesting ter­ ritory for 24 days after nest leaving. Grace Townsend observed that Y33 was chased by the male parent when it ventured back to the nesting terri­ tory on the 29th day after fledging. 113 NESTING SUCCESS Table 24 summarizes data on nesting success in East Lansing and Pittsburgh, fledged. A nest was considered successful if at least one young was The percentage of success in East Lansing varied widely from 100 in 1954 and 1956 to 47,8 in 1957, 1954 and 1956, However, few nests were observed in On the other hand, the percentage of success in Pittsburgh only varied from 61.5 in 1955 to 68.8 in 1956. I found desertion and predation to be the major factors in nesting failure (Table 25), in East Lansing, Nine of the 12 deserted nests that I recorded were Two of them contained nestlings, and these were abandoned after two days of cold, wet weather. However, the only losses that I attributed to weather were those nests actually destroyed by storms. It is thought that the use of insecticides is responsible for some desertions. Of 18 young of different species in a sprayed area, Benton (1951:26) found only 8 (44 per cent) fledging, while in a similar unsprayed area, 15 out of 21 (71 per cent) fledged successfully. Howell (1942:549) writes of the robins* preference for evergreens during the first nesting period. Koehler and Koehler (1945:17) found that 49 out of 64 (76.6 per cent) nests in spruces were successful. That there is an advantage in utilizing evergreen trees for first nests is indicated in Table 26. The percentage of success for nests in conifers was 75 while that for nests in deciduous species was only 44. Many of the nests in artificial sites were well protected and these show a relatively high suc­ cess (66.7 per cent). 114 In Table 27 data for nests that I was able to follow from oviposition through fledging are given. and Young1s in Table 28. My data are then compared with Howell’s Of 501 active robin nests, Kendeigh (1942) found that 390 (78 per cent) produced at least one young. Since he did not check some nests after the nestlings were well developed, his data are not in­ cluded in Table 28. From a survey of the literature on open nests of altricial species, Nice (1957) calculated the success of 7788 nests as 49.3 per cent, hatching success of 21,040 eggs as 59.8 per cent, and fledg­ ing success of 21,951 eggs as 45.9 per cent. markedly similar. The data on robins are The average number of young produced per active nest would be 1.3, and the average number per successful nest 2.3. Young’s data are interesting in that he recorded the lowest percentage of success­ ful nests, which, however, yielded the highest number of fledglings. The fate of the unsuccessful eggs and fledglings from Table 27 is given in Tables 29 and 30 respectively. Some that disappeared from nests were probably taken by predators, but I did not attribute loss to this factor unless definite evidence — e.g., shell fragments, wounded young— was found. Young (1949a:45) observed that 14 out of 46 (30.4 per cent) eggs were punctured by an avian predator, perhaps the common grackle. The 11 young whose loss I attribute to predation were probably killed by man and other mammals. One young of nest 54-45 was shot by a boy; one of nest 56-36 was killed by a cat. lings from nest 56-10. Claw marks were on one of the four dead nest* Nests 55-9 and 55-13, which contained a total of five young, were smashed. The fate of at least one nestling in nest 55-2 was unusual. Two young disappeared before May 13 at which time the other two were found on the ground beneath the nest. One was still alive and was returned to the nest. 115 Stoddard Smith reported that the female later took this young by the leg and hurled it from the nest. 116 FOOD AND FEEDING BEHAVIOR Food Materials Many data have been published on the diet of the robin. From a sur­ vey of the literature, Brooks (1939) lists about 80 published references, Beal (1915:5) reports on the analysis of 1236 stomachs secured at various times of the year. In his study 42,4 per cent of the food was determined as animate material, chiefly insects, while the remaining food items were principally fruits and berries. seeds. Beal further states that robins eat few During a period of heavy snow in March, 1956, a male and female ate many seeds of the foxtail millet (Setaria italica (L.) Beauv.) at my feeding station, and they continued taking them for several days after the snow melted. Martin et^ al_. (1951:149-150) have data from 1423 specimens, 442 taken in winter, 316 in spring, 514 in summer and 151 In autumn. percentage of plant food was 64, 21, 60 and 81 respectively. The Caterpillars, beetles, and earthworms were the predominant animal foods. During two summers Hamilton (1940, 1943) studied the diet of robins at Ithaca, New York, by examining collected droppings. In 1939 the fre­ quency of occurrence of different food items in 700 droppings was deter­ mined as 80.13 per cent animal matter and 73.14 per cent plant matter. The plant families predominating in the fecal material were Rosaceae, Solanaceae and Caprifoliaceae. In 1942 plant remains occurred in 81.5 per cent of the droppings, with barberry (Berber!s sp.) as the most Important plant material. Of animal matter, which was found in 93.5 per cent of the droppings, beetles were the most prevalent. 117 Feeding Behavior When a robin feeds on the ground, it probes into the soil from either a normal posture or a crouched one. Frequently, when it feeds from a crouched posture, it cocks its head to one side before probing. the downward peck produces food, sometimes not. Sometimes Of 61 successful probings that I recorded, 16 (26.2 per cent) were made from the normal posture while 45 (73.8 per cent) were from the crouched one. Twenty-six of the latter (57.8 per cent) were made after the robin cocked its head. The question arises as to whether the robin cocks its head to see its prey better or to listen for it. Acute eyesight was demonstrated when a robin would suddenly run forward a few inches from a normal posture, peck at the ground and obtain an insect or other small arthropod. On June 5, 1957, while feeding on small worms in the lower level of a bird bath in Area 3, Y76 cocked its head before two out of five successful probings, even though the worms were plainly visible. On June 14, 1957, while col­ lecting elm samaras on a street in Area 3, the female of nest 57-20 cocked her head before three out of seven pecks. was certainly not listening for prey. data on the robin1s hearing acuity. In these two instances the bird Unfortunately there are no available However, Jackson (1951:344) observed a robin directly under his gaze taking earthworms that were not visible at the surface, from a depth of about three-fourths inches. It is possible that the observer was unable to detect the movements of small soil parti­ cles, which the robin could see. When robins fed in leaf litter of woodlots, they scratched in the leaves, pecked at them and threw them aside. When they took fruits from trees and shrubs, they usually perched above or below the food. On two occasions, I noted individuals hovering in the air and snatching fruits. 118 O n June 25, 1955, while fluttering near an Amelanchier shrub, F3 picked one fruit* On September 13, 1956, a few robins feeding on wild grapes and black cherries in Area 3 flew from branches up to fruits, took them on the wing, and returned to perches below* Bernard Tan Clsve told me that he observed similar behavior of a female gathering ants from a tree trunk. Cleveland (1923:254) watched robins catching periodical cicadas (Maglclcada septendecim (L.)) in mid-air as well as moving over the tree trunks like woodpeckers in their search for these insects. Hodges (1948:164) noted about 12 robins feeding on aquatic insects as the birds skimmed over the C surface of the water and even plunged into it. Communal Feeding Areas Robins spend an appreciable amount of time in flocks, which frequent open areas as well as wooded ones. This behavior is particularly evident before nesting begins in the spring and again after nesting in the summer. In both East Lansing and Pittsburgh, robins were found in increasingly large numbers in wooded sections from late June until August, when prac­ tically the entire population had deserted urban areas. As early as the last week of June, I found young feeding on the red-berried elder (Sambucus pubens Michx.) in woodlots of East Lansing. Some robins were found in all wooded areas that I investigated in East Lansing in late summer, but the largest numbers were always in a woodlot northeast of the East Lansing Junior High School on Abbott Road. In this woodlot there was an extensive thicket of buckthorn (Rhamnus frangula L.), which not only provided food but also protection (Plate 6-B). Common grackles, starlings, cowbirds and cedar waxwings made use of this site as well. The robins fed on the buckthorn drupes, as well as in the leaf lit­ 119 ter of the woods and on adjacent lawns* In 1953 the first record of robins making use of the buckthorn thicket was on July 29, after which the ripen­ ing fruits attracted many* The droppings of birds were colored a deep blue, and it was easy to note that birds feeding on these fruits ranged throughout the woods as well as on the nearby lawns, streets and sidewalks* Robins ate the fruits whole* On August 6, 1953, one individual took three drupes-in one-half minute; another took five in three-fourths of a minute. This 25-acre woods was disturbed by construction in 1955, but robins con­ tinued to use the area* From 7:45 to 8:15 P*M. on July 27, 1957, I counted 70 moving from the woods to the high school lawn nearby before they flew to the night roost# One robin was collected in the Abbott Road woods in August, 1954# Analysis showed that 90 per cent of the stomach contents was composed of beetles belonging to the family Eisteridae, 1 per cent to the wasp family Calcidae and 9 per cent unidentifiable. The stomach of one collected in a Pittsburgh communal feeding area on August 4, 1955, was filled entirely with the pulp and seeds of bittersweot nightshade (Solanum dulcamara L*)* Wear Area 2, a woodlot adjacent to a municipal golf course attracted robins in late summer. Both Crataegus and black cherry were plentiful. The birds fed on fallen haws, some of which were soft and rotten. One young took a haw in its bill, beat the fruit on the ground and took three bites in 30 seconds. This same individual speared a haw and moved its beak so that it was able to get a small piece. The bird then threw the remaining part to the ground and later retrieved it for another bite. Communal feeding areas which attracted robins consistently had the following characteristics: a good supply of fruiting shrubs and trees, areas of exposed leaf litter with little herbaceous cover, and adjacent ISO expanses of lawns. To determine the type of food items which flocks of robins might utilize in the leaf litter and soil, four soil samples were collected in 1956, two from the Abbott Road woods and two from a small woods on the Red Cedar River in Area 5. A six-inch square was marked off on the surface, and all of the soil within these bounds to the depth of six inches was collected. The animals were counted and identified as follows. Sample Lumbricidae Other Oligochetes Coleoptera Adult Immature Abbott Road 1 1 Histeridae 1 Carabidae 1 Scarabaeidae 1 Curculionidae 2 Curculionidae 2 Elateridae Area 3 3 IV 4 32 1 Elateridae Four post-nesting recoveries of banded robins were made in woods used as daytime feeding areas: F4 in a woodlot of Area 1, 525 feet from her second nesting site on September 3, 1955; FI in a woods of Area 2, 375 feet from her first nest on September 30, 1954; and two young of nest 54-40 mentioned previously. Whether they utilized the same area for any length of time was not determined. In August, 1954, I banded over 10 young in the Abbott Road woods, but I was not able to find them on succeed­ ing days • Drinking Water During an eight-hour period I watched three robins as they came to 121 drink water at bird baths and pools. form, approximately 70° F., when it came to water. Length of Observation in Minutes Usually a robin took more than one swallow The tabulation is given below. Beakfuls of Water Beakfuls per Hour Bird Time s at Water 130 54-45 female 1 4 1.8 44 54-45 female 2 8 10.9 153 54-45 female 3 24 9.4 54-45 male 1 6 4.7 1 1 .8 8 43 5.4 77 72 Total The air temperature was fairly uni­ 476 FI 122 ROOSTING In the evening robins fly to roosting areas where they remain until early morning, Howell (1940:21) writes that during the nesting season only the male goes to a roost while the female remains on the nest. Later when the young are able to fly well, they also move to a night roost. Before leaving their nesting territory or feeding grounds at night, robins exhibited considerable restlessness. They flew back and forth between the ground and perches in trees or on houses, often giving call notes. Sometimes they joined other robins flying overhead. From one to two hours before sunset at the Abbott Road woods, robins moved from the buckthorn thicket through the eastern part of the woods to the open areas beyond. I observed the same behavior at the communal feeding grounds near Area 1. Here the robins shifted to the adjacent golf course before re­ pairing to the roost. Abel (1914), Bailey (1932), Black (1932), Bolander (1932), Brewster (1890), Ganier (1924), Howell (1940), Pearson (1910), Speirs (1946), Stover (1912) and Toungworth (1929) describe roosts and/or roosting be­ havior, of which Brewsterrs account is the most complete. Most of these roosts were in wooded areas. Robins commonly roost with other species of birds, especially starlings, grackles and cowbirds. I observed this at a roost in a resi­ dential section of East Lansing and at one in a woods directly north of Ingram, a suburb of Pittsburgh. The roost at Highland Park in Pittsburgh was composed almost entirely of robins. 123 I made observations at Ingram only in the late summer of 1953, Situated on a northern slope, the roost covered an undetermined portion of a second growth wooded area that was about one mile in length and onefourth mile in width. There were many Crataegus thickots. East Lansing roost in the summers of 1953, 1954 and 1957. I studied the It covered somewhat more than six city blocks, with minor fluctuations in boundaries. The roost in Highland Park was the densely shrubby northern embankment of a reservoir plus adjoining wooded areas. The shrubs, largely mock-orange (Philadelphus coronarius L.). were from six to eight feet in height. Bernard Van Cleve and I studied this area from 1955 through 1957. Figure 31 shows the flock size that Stanley Belfore and I recorded at the Ingram roost on two evenings in 1953. No attempt was made to count the total number of robins, since they were arriving from a number of directions. It can be seen that they arrived singly and in small groups, which were loose, straggling ones. 50 individuals. The largest flock was composed of about Likewise, most of the aggregations that Brewster (1890: 369) and Stover (1912:170) observed were small. However, Youngworth (1929: 105) records robins coming to a roost in groups ranging from 150 to 200. At two winter roosts, Bolander (1932:142) and Pearson (1910:208) describe some flocks as enormous. On five clear evenings at the Highland Park roost robins flying into the area were counted, and at five-minute intervals the light intensity was measured with a Weston Master Lightmeter (Figure 32). Flying at 100 feet or more above the roost, the early arrivals descended toward the vegetation in almost vertical dives. to drink or to the lawn to forage. Sometimes they went to the reservoir With the advent of darkness, robins streamed into the roost in progressively larger numbers, sometimes only Figure 31. The composition of robin flocks arriving at the Ingram roost in Pittsburgh on the evenings of August 27 and September 11, 1953. 124 IS O zoo 100 N V MBCH 50 of F L O C K S j FLOCK z C O M PO SITIO N ! 3 4 ( M UM 8ER 5 6 OF IW D W ID U A L S ) *7-8 9*10 U'i5 lb-10 2i-ZS 24 + Figure 32, Arrival of robins at the Highland Park roost during five evenings in August, September and October, 1955* 125 500 400 300 200 \00 N/L»/-1BER OF R o b in s 200 LIGHT IKjfEKfSlTV IN FOOT CANDLES 126 five or six feet above the shrubs. 370) made similar observations. Abel (1914:172) and Brewster (1890: Bernard Van Clevefs observation on January 15, 1956, indicates that robins may experience difficulty in find­ ing the roost if they arrive after dark. He found about 10 robins flutter­ ing about the guard rails of the reservoir. It is thought that they left their feeding grounds late, and that with the onset of darkness the ring of lights around the reservoir attracted them. At the East Lansing roost the majority of robins arrived after the starlings, grackles and cowbirds, which occupied the central part of the area. Consequently, robins were concentrated in the periphery. In the morning robins left first, and at daybreak many of them were on nearby lawns. Gradually they spread back to communal feeding grounds. In August, 1953, I noted that few if any were at the daytime feeding area in the Abbott Road woods until about one hour after sunrise. On the other hand, Bolander (1932:143) and Youngworth (1929:105) observed robins leaving night roosts in continuous streams. evidently leave the roost very early. During the nesting season the males On a visit to a roost on June 17, 1941 at 3:35 A.M., Speirs (1946:78) found the area being rapidly deserted by the robins. 127 SUMMARY The life cycle of the robin was studied in Pittsburgh, Pennsylvania, and in East Lansing, Michigan, during the years 1953 to 1957 inclusive. The seasonal distribution was observed at a roost in Pittsburgh. The first spring migrants appeared as early as mid-February or as late as the first days of March. In the fall there was a decrease in robins until mid-November, when the winter population usually became stabilized. With the exception of the winter of 1955-56, when there was a heavy crop of various fruits, few wintering robins were in the Pittsburgh area. Of 29 winter (November-March) recoveries of robins banded in East Lansing, 69 per cent were between the latitudes of 30° and 35° N.; many of these recoveries were almost directly south of East Lansing. Several threat postures and displays, some similar or identical to ones described by Dilger (1956) for the genera Catharus and Hylocichla. are used to establish and maintain territories, and to intimidate other robins as well as other species at communal feeding areas. Several observations suggest the existence of some relatively unde­ veloped form of courtship feeding in the robin. The whisper song has a dual purpose: it functions in the establish­ ment and maintenance of the pairing bond and also serves as a threat. A probable role of the carolling song, which decreases after the eggs have hatched, is declaration of territory. Songs were given on perches ranging from ground level to a height of 60 feet. showed some preference for one song perch. Resident males in territories One flight song, which has been recorded only once in the literature, was heard. 128 A definite trend in song cessation was noted by the first part of July in 1955 in Pittsburgh, and in 1956 in East Lansing, of the season were heard the first week of August, The last songs In Pittsburgh, with the exception of one year, there was a period of song resumption during Septem­ ber and the first part of October, some of it undoubtedly due to the first songs of birds of the year. The populations of robins ranged from 12 pairs per 100 acres in an aspen community of northern Lower Michigan to 120 pairs per 100 acres in suburban areas of Pittsburgh. In East Lansing numbers of dead and dying robins, the declining populations, and the failure of adults to produce young are believed to be due to DDT and other insecticides. Maximum territory, determined according to a method given by Odum and Kuenzler (1955), was about 2.5 acres in three instances. Utilized territories, determined by 20 or more irregularly spaced observations, ranged in size from .24 to .87 acres in 12 cases. There appeared to be a correlation between territory size and population density. In late April and early May there was a peak of nesting activity in Pittsburgh. Two peaks of nesting activity were noted in East Lansing in 1957, one in late April and early May, and another in late May and early June • Several females were observed testing potential nest sites, but some male 3 appeared to influence the selection. gan after a rise in temperature. The first nesting activity be­ The average time for construction of 12 nests was 4.5 days. Twenty-one per cent of the first nests in the Lansing area and 29.4 per cent of the first nests in Pittsburgh were in conifers. In Pittsburgh 29.1 per cent of all nests were in artificial sites while in the Lansing 129 area only 2*1 per cent were in such locations. The lack of tall shade trees in Pittsburgh study areas probably forced robins to make use of artificial sites that offered adequate height# The average height of 83 nests in Pittsburgh was 14.5 feet, and of 48 nests in the Lansing area it was 20.3 feet. These heights were greater than those found in undisturbed areas by other workers. females. No preferred height was evident for individual However, the second nest was usually higher than the first. The distances separating nests built in the same year by known females varied from 25 to 230 feet• Linear measurements of 17 collected nests and the dry weights of 19 were determined* An undescribod species of Protocalliphora was found in 40 per cent of 20 nests collected in Pittsburgh. Five of the eight par­ asitized nests were successful in producing young. Six other examples of arthropods were also found in robin nests. For seven nests the average time between their completion and the appearance of the first egg was four days. The mean clutch size for 42 nests in Pittsburgh was 3.4 * .11, and for 13 in East Lansing it was 3.5 ± #18. A decrease in clutch size was evident in Tune. cubation period for 12 clutches was 12.5 * .19 days. The mean in­ Twenty-one periods of attentiveness by the female averaged 36.4 minutes, and 23 periods of inattentiveness averaged 6.3 minutes. Several observations of males sitting on eggs were made. The mean extent of the nestling period for 37 individuals was 13.9 £ .16 days. For approximately 16 hours of observations at seven robin nests, the feedings to the young averaged 6.4 per hour. Adults ate excreta in varying degrees at all stages of nestling growth. The average interval between the fledging of a first brood and the completion of a second nest 130 was 11*4 days in five cases, and between the fledging of a first and a sec­ ond brood it was 41*7 days in three cases* The mean extent of the fledgling period for 15 broods was 14.9 ± *74 days* It was divided into three stages: Hiding Stage (0-3 days after fledging), Early-flying Stage (4-6 days after fledging), and Semi-dependent Stage (7 days after fledging until the young became independent)* Three sets of fledglings confined their activities to areas ranging from one acre to 5.Q acres. However, some young moved considerable distances a short time after they left the nest. Nesting success averaged 66.7 per cent for 36 nests in East Lansing as well as for 48 nests in Pittsburgh. First nests in conifers were much more successful (75 per cent) than those in deciduous trees (44 per cent). Desertion and mammalian predators were major factors in nesting failures. Of 161 eggs, 70*8 per cent hatched and 49.1 per cent produced fledglings. The robin probes in the ground for food from either a crouched position or a normal posture. food. It depends primarily upon eyesight for obtaining After breeding, robins feed in flocks, usually in woodlots adjacent to open areas, where there is a good supply of fruiting shrubs and exposed leaf litter. During eight hours of observation, three robins took, on the average, 5.4 beakfuls of water per hour. Three night roosts were observed: one in shade trees along East Lan­ sing streets, one in a second growth woods in Pittsburgh, and another on a shrubby embankment of a reservoir in a Pittsburgh city park. Robins usually flew to roosts singly or in small, loose, straggling groups. With the advent of darkness they moved into the roosts in increasing numbers. the morning they spread back to communal feeding grounds gradually. In 131 to aj * * © w d H K M M H H M M « M W W M w M CV2 * cd o © £ ra © © d < TO d R © d 6 «H © CO © Xi R 1 O o o xi o o o ■H b£) © rH © f t © d d R © © XI o •H d TO X d rH o o © d X 3 d R © d d © o o TO © rH H R d rH O X o <3 ft © o d d •rH rH O d © O TO d d d R a © o © © 54 © © d © CJ © *H d d © 07 © xl a. d I o o o o S TO © M t> © d I ft CO Pi *H rH o d CO © > TO d © d X o 0 M © © 1 Xt d M © R o TO tjD d ■H d s o S3 TO © i— 1 rH *H d 1 J*4 O © rH ft ft i—4 te o xi o © © d o CO •H & © 1— 1 £ o © Xi R d d X bo *H © © PC < r- © X to £ TO ft TO © ft ft >> © 1 5 •H Xi o £ © © a. TO O o © to d iH ■ TO I © )— d > T O -*— I iH T O C 'r>H TO d •rH 3 TO © ■rH rH rH © X < TO © Pi to o -R & c R d O * © Xi R S * * 132 to © © M K M OJ © © p <$ Table 1 (continued) K M P < 55 ■©H S-H t4 P © © ■rH o CO w M © © © H O © o ro p H © p ro © p © p o o o o o o p © •rH p o ro © .© o »© P> p © © © X> © 0 -P PJ © •H 3 -H {>3 53 ro © © P -rH ro © p o p © o o 1 © p p -© © © © p © p © © ro CO ro ro •H ■© ro © § o p pH -rH P © © P P •H O o © r ”! o •H rH -rH & © O •H P P © P o rH o o *rl fO ro 0) P © PH L 3 pH p © © Mo © Pi nj o o P © o © pH *© o o £ t>» H

; p © Eh .© 403 © © © •© © o © © © EO © © © mH ro © < — t © r© o p © © w ro © ro © ro o rH rH -H fc* P w xi p © © © I 4* © © T» © ro © © © p © xi ro © © p x> 1 p © © P J3 © © ro © t§ *H f-H P p *H O P P o o © © O p pa 133 co C Oi ff 0 H M M M M K O H H K M < w 0} © as © 0 H O M O M W M H K M M M M W s 03 CM T3 0 0 0 0 •P P 0 O o 0 i —I r O 0 E-» 0 E 0 55 O •i-S <0 ■P -P S3 0 •H rP o o 0 0 -p > 0 0 > r— f •H tic o 0 0 1-1 r> w 0 o *1 — 1 p 0 0 E o *0 0 © w 0 0 Pi 0 a S3 Q O O o 0 0 *P l> X 0 2 p »0 O O 5s bQ S3 *rA i"4 0 0 P CO 0 0 >> 0 1 0 0 P5 & o Ei Et 0 Pi T O X> 9 0 0 0 O W 0 i— t 0 fO rH 0 M 0 0 0 © P © M © i— 1 o *H Et O © Et O E •P P r-t 0 CD 0 iP 0 O 0 •P 0 0 El 0 P 0 0 0 1 — 1 0 O 0 •H 0 O’ 0 0 Ei X P o I— 1 o JS © i— 1 M o 0 Et bC 0 O g o o C O ■p <0 0 0 •H *0 0 0 o 0 0 © •0 0 o E X o ■H P3 0 0 © 0 0 o 0 0 P 0 © C O 0 0 Pi Et •H X ? O o X © •0 0 © X 1 0 £ O 0 CO 0 -0 P 1 — t 0 0 •P X 0 0 O g X o bO -p *0 0 IP 0 •rl P 0 •H 0 P 0 0 0 ■H P CO X o 0 •P

> 0 © o r-t •H p *rH Pi © © X & s o p *0 © <0 •P © t © 0 O <0 0 P3 0 0 •P 0 0 •rl •0 © 0 0 r—t 0 i— 1 i 1 P P o 0 P 0 — © N i-t P CO £ O 0 0 0 P W bO 0 -P P P •H X o N 0 O <0 © ^5 B S o 0 0 0 p © bo 0 o co *3 p o 134 to cd ® d <1 cd © M M W H M W H M H M M cd © M H M H M M Some Mammals of the Study Areas 3 © to •P P a © P O CQ to «P > CO P a i — ( © •d P Pi © S3 d Q O O CO o a P P o 00 © e o p o P d o p d •H b 0 d o o p d o o o o od PJ ro 03 f>! d PH © 2 c0 P d _p co P nd O G 2 r a © o a o cd M CO 2 © *H d UD 00 cd d a © •H < a *rt H P r— 1 © p CO o o p p to to o & cd p E © V q 3 E 2t •rl -d © d d © © P o cd W e c to d © 60 d to P 2 o •rl tsD © > d O d a E 3l o to •p 2 C O 2 CO « cr1 cd pd o p P C O W a I—I > ed 5? d o to P •H cd p d o p p o o d d © P C O cd pa © p o 135 !>» © © > o o © Pi Pi CM TO © at East Lansing, Michigan of Robins Banded Recoveries © © (2 © © TO © © M £H Pi <© •» * •© i— l TO O o P o TO © © o S TO TO TO to •fH co t H a © Foreign © © *M O o © X PH © © •H rH O © © o © Pi O © •r-f <© © *« H E3S p © o CO © © © © c tiO •H s £ *© © t-i O © © Cd to CO cn rH £>CO cn i — ! i— 1 cn i —1 CO © > o O > © « e © X o 2 to CO cn rH CO © © X TO Pm o © © p © © Jtf 2 iiD 'd © Ml rH co co cn rH © TO X S TO > O o rH P=i •* © © © © £3 P © O Pm Cs D •H £ r© © 1- 1 © <— 1 X *M fc* rH © TO TO © ti D •rH © •rH © o rH pM «* 5 *1 P ♦rH O © © ex tsD •rH £ T3 © Ml •rH 04 ©4 •M TO TO *rH TO TO X 2 n © X r. TO bC © H © CM CO 1— I © Pm 1 © P TO 2 © O bO *rH ss 'Ct © XI •rH ss *© © XI © o P CO rH co © X © rH < p i— to © © © •rH TO •H © o t-l © rH i— I H t> #* CD P © © •rH 53 CO CO cr> to to cn to cr> i—I 03 in i—t XI o Pi © 2 X Pt XI o © © Pi © >> © © © © CO cn 03 03 >> © © X 2 © © Pi © © EiO •M £ •© © cn to to #» p < CO 3 cn •*— 1 Pi CM •M TO TO fH TO TO iH 2 © © © to 03 CO cn •» CO 03 rH © © M E © *© X © © © •> t>> © © XJ #h © rH rH ■ rH t> -H Pi PM •r H TO TO •H TO TO •H 2 to 03 >> Pi © © © tO 02 cn i—l 03 >» a © Pi XI X Pm Pm © © *© © © © PC $ © © X! nd TO *© in CO cn rH 9 PO rH in i— 1 s CO •— i cn rH 03 o 1— 1 © £ to X >, c© rH CO rH cn rH CO A rH tn © cn 2 rH © X 03 CO Cn X to i> > 03 03 X © 2 2 X © 2 2 O CO 03 in X ©< in i—i DtO in 03 *© in cn X to X CO in in o 03 O CO 03 oX 03 cCO <*: o cn i—i 03 Cco < o 03 ts O cn CO 8 03 s 03 < © s 03 tD tO CO PC >5 2 cn to tO CO PC in 03 cn CO K *> X X 03 CD CD in in 03 CO o © 03 CO 03 CD CO O CO to 03 O co 136 © © & © t> o o © Pd © t j ) t u o rH >» o P © O +» d © o © .H PH rH Ph TO TO © -r-i TO *H © r*> P © o t-} m © to •H £ 'H ►h 60 •H 3F 'TO T O tH cn co cn Table 3 (continued) C7> rH O Fh © t* CD o P o © © pi Pi <13 CM © Eh O 23 © Fh CO <+H © © TO T O 0 d «• © d o o Eh o >> •H © § cn cn CM cn *H rH «* o CO TO •H 60 Fh O 9 05 *» o Fh O 0 TO © P T O P 00 00 •rH & rcJ d i- i o CO cn rH O •rH Oh Oh •rH TO TO •rH T O TO •rH 3 A O h O h •rH TO TO •rH T O TO Fh TO P CO cn rH tO 4k © © O o Fh PQ to to T O « rH •H 60 •H £ ■0 d pi to < (— 1 d 3 rH M rH TO T O *ro < — 1 P p T O P © TO •rl i— 1 f— t • rH d •H 3 Fh PC T O PC 3. 60 & © © Fh 0> © to •d o Fh © £3 Jd O Fh TO S3 © P*H >> Fh T O d Fh 0 © Fh © 0 s © o © pH ■rH TO CO •rH TO *h 60 Fh TO TO d Fh © 60 •rH & m © O h ► H o HEfl cn rH a to Cn i—i O » rH o to o» 1 — ( rH Fh P TO •9 d SdP < © © > o 23 * >> Fh TO d d T O t —> TO i— I 4k < «H ft 1— 1 •r H > -d J>» © T O O W TO 23 60 60 *H £ •H £ rd •0 6 a 8 p © O T O 4k d o TO TO & ’S 0 O TO TO > —1 < © p 4k 3 Fh T O d Fh 0 ■H P h O h •r H 0 0 •H TO R TO TO 5 TO d ►-3 d *-1 Cn CO cn cn CO cn rH rH d CM >» e-t to T"l *iH 4k cn CO rH rH d TO i>> T O d d t>) Fh TO d Hi d TO Hj o to cn CO TO 60 £ * 0 d 0 d t-1 CO rH Fh d i * S to cn t <— rH H1 cn iH 44 4k Fh TO d M TO © cn Cn 4k cO © © 60 © CM cO rH & -d o Fh TO 2a o Fh TO 3 *0 © *0 d © TO 60 fq - ■TO T©) § w © P TO Q O 5£ nd d TO PQ cn CM cn rH «* iH rH H Fh Oi < CO CO cn rH •k *H © d 3 *-> 8 cn rH * CO 1—( © d d Hi CM CO CM in cn cn CO rH <0 rH to to CM <0 CO CM cn > >> 3 TO © P O P O 3 o «=i CM to to t> co 0 00 tO O rH CM iH CM 1 4k to CM © d i—1 = < — 1 TO o to to a> 8 cn c^ 3 TO 3 TO 23 1—1 to to c^ ^}* Hi CO 1 S1 to to o 8 cn i—I co rH Ht to to CO TO 3 o to in Tr 1 oto to 1 IN to 137 © a ♦rH X © Fh o o © K o © o ctj rH to rH O Fh © O xi -4> © o CO a © © Fh © P i O O © « Sf © E©h M S r© TO © O to -H to bO •H £ bD •H £ Q d © © M © Eh d 3 to d 3 to £ d 3 to cd CO CD rH d 0} 3 3 •p Pl o o •rH t» O o © © to PCS « «% 02 cn r ’i Fh >> © 3 Fh to © CO CD rH to PQ ^ a © CD CO CD r—f d © d § PQ © © P o S3 d a © pq CD CD CO CD a> Fh to i —i to © o ■a © 02 to 4-> Ph Hi S CO O to to CD I— I CO © CO CD to I o CO CO CO I © 02 02 CD rH CO I to CD 138 & © o © © Cd © O +3 O cd to 03 to to CsO to {£ .£ to P to to 2 to 8 a 03 A to ID to 04 to to P Ha ** HI f-t » © +3 to d to P d o to o & cd d to taO cd CO WD to ■rl £ t to tiO & •53 3 d o to to to s © W taO to £ 'S 3 03 to to Pa cd to d cd Fh o tboO 3 CD 03 CO 03 !*■*{ cn to d o +3 cd to dO to 04 SI! to o o d o +3 cn to 03 to to cn to 00 to © d P Ha H «* 1 — 1 •t to 03 FH Fh © to cn © to O +3 O O © 03 CO 03 to m> cd S3 0k O 03 >n cd to * CO 03 to •« IP u © ■§ 43 O a Ha 03 03 O 03 to 03 to < to to S cn to •rH FH P. to to cn to 03 © O •t 03 rH IP o 03 d P to CO 0k H CO >a t© rrn 03 © 43 & to o 55 d cd to IN 03 IP IP O 03 O 03 < c to CO a to P Ha to 03 to to i—f to I to of the year to © •cs d to © -p cd o 03 CO cn *Young Michigan Recoveries of Robins Banded at East Lansing Ph >a 43 139 i>» rH a TJ d a> 3 rH cd -— CO —. to Fh cd © 'd d 05 d rH cd co -- CO . __ © to P h 05 a rH © > ■ _„ >> •d d p (0 t p 01 01 01 P •rl t9 * to * CM CM CM P CO d ejn p » d d o CO +3 C O * * o p s © t-l to d <3* d rH rH ID ID P P C O d P P ID P to © d d © d <3 < -K ID * P p > ^ 3 £ *~3 <$ •> O CD P TO »>» d •a 9 »-5 < 3 o p © d tiD d << CO CM CO ■3 1-5 h CM CO dates C5 CD < < a rH O Cti *rH Fh P © 03 ID © d CO >» £ < 1-5 P » CM d *h •H P 00 d cd d cd P M CD CD C DO PQ >5 rH d O >» 'S < d d E P P CO E-c ID rH u >> 'B p CO O d o •H p cd o o p Fh cd W w *dd d p cd Fh rH D< C D CO M •CJ CM P TO >5 a ■3 1 CO to rH CM rH rH d d H> *=C *-s Ha o 'tjc tO cr> rH I oCM 05 rH O CM >> >» rH d >3 rH d 3 H> 1-5 o> rH I rH to tO CD 05 the earliest * O rH o (SO o and latest * 05 ID 05 rH 05 rH 54 d cd >5 d PH P C D P o o *d rH d Fh cd Lo tao>h © rH rH tfk d cd p CO £ © < » P d o p ©p tH o > TO a Fh a © FP Ph © © *fcS § Fh t> d rH 50 >» TO P a p © pH p PU TO cs W) d •rH TO © © M P a © &o p xt TO O © P W a ‘•'Average date appears below **Last day of observation Song Cessation of the Robin 9 140 c a I © © p 11 I XI I 0 X © ;3 N xl c and Conditions Under M H ■g £ Which They Are Given £ P Xi H rH rH X W 9 3 0 K HI K M M M M W M Xl £ Ph CD of the Robin * M Hi M HI M HI * M M HI P times © XI o 0 ,— .. d o •rH P •rH d a o o o Fh P 0 G 60 0 G rH •rH 0 p ^3 o © rH © CO rH >> O h X* c h CO © d 3 e © pH 63 d p d •— t •rH d PQ 0 t p u 0 0 0 d o 0 Fh s P h P, 0 X d ra © 0 P CO © d XI P o d 0 0 0 0 w 0 ® > e 0 0 i— 1 o 0 xl P •rH £ HI 0 Fh O P 0 d 0 d 53 3 xl p •rH ps P to 0 H © 3 d 0 Fh O d 0 0 e d ■ *> P co © d p 60 d P 60 d p p co l> 0 o o p rH © Fh p rH d d < P rH d d > co P © •et <© © >> P r-t o ft © d o © Hi © ft © d O •rl © d ft cn © _ © I—1 d ft o o hi O e d Fh P d •rl © p © e WJ © P d •H d -rl ft rl *rl Hi © O U © P Hi © •rH P o Hi Hi © P P O d © CjD d •H to P © £ p o © E-< Hi d O o F h Fh a P © F h O © © P •rl d © p to o o P •rl © to © © d o S O Hi Hi © ft o P o P p M O d d € o Fh ft © •rl C O P w & ^ ° iH P d Fh p p •rl rH O c P -rH S’ ft iH d rH M flH »© © •© Fh o o © *cn 142 e ft g t ft 0 M © 43 CO II I 43 ft I K • 0 ft © d O ft © PC 34 0 d •d ft < ^Recorded Table 6 (continued) P 143 o d © U u©© CT> * CD 3c co 00 00 CO cn & O ►d d d © £ o o id id O *rH SB S5 SB © w X p P X Fh O Fh d Fh © Xl P Fh p Fh © to p p to £ o p •rH p O Ok P p p d « W ‘H rd O *H d d Fh © © bO xi t h P rd Fh © O t H S3 a m © F 0 < HH © Fh O h d © Pk © ©1 F *© d O© h Fh © o id d d Fh © XJ p Fh O 53 © bO •rl o •H F 1-* © © 8 Fh © § id § id d d Fh © © w X ? •h P XJ Ft o O •H ^ a d Fh © X! P Fh O S3 P d © b0 ♦H xl o »H a rk oo rd © p O X) © © r© id H author’s data 144 in in cn a o c £3 t 1 1 T 0 rO X X at e X X tn in cn i— 1 9 ►rl Fh £ •r H Fh ft CO CO in cn in in c n i— t n ft #» c n « in c n i— i t* «• 00 0 0 Fh © E 0 0 © •rH E 3 Fh f t Fh Fh CO CO CO 0 0 a X ft d •i—i ft nd © X ft r— I *rH t> -H © x +3 © © Xl -P © © X © 43 tH ■s © © Fh X « rH o d ft CJ1 Ph TJ •rH © ft esO W to o © rH d © s? o © Ci x © e ft © © a •H X © Fh O X Fh <£ Fh < s d ’H d •rH •H C Q d o o m X d o ft •■<- o o o d o •rH © TO •rH X © X 3 o •§ »d M o TO X d © X © Fh O X TO d o © T O •rH ^7^' «h d o TO •rH rd © la X © Fh O X «0 1 © & © < +> o td o to d o d i— I r— 1 cd cd © © © © © © © Fh < a a a © © Fh < 00 ■a OD *tS lib tl) x § « X TO x x •rH ft X X X X X *rH X X •H X X ft ft ft *1— 1 o © ft © d C Q d o o TO X r' „ d o T O X •d © Fh © £ O © Fh © © tifl X X -P d Fh O O X S3 s author’s data © from + 3 •a Fh d x ra + 3 -P ft X Fh d to ■p +3 ft -P +3 ft © © © •rH ^Calculated o © S -rH Hi tn cn o x cn i— i © in tO X o- Table 7 (continued) 00 Cd 145 © o C! » T3 TO C O 'TO TO P ra >» •TO TO P C D C D •iH ra •rH fS ft ft 'TO P m P w h H ra •H ra •H s £ £ C D TO TO TO © © ft Fh O ro "in' 'co' o- TO) C > CD CD CD in in in Sf ft CO CO TO © ‘ TO p 03 TO nH ft TO W 60 P TO o •rH o g ft w T O to CO T O © TO © a a ■s Fh 60 TO •rH ra TO TO ft ft TO O P ra TO PS TO n ra p p •rH ft in Fh ft © TO in • in -rH Fh CO Table 7 (continued) 'TO 3o •rH P Fh O co TO © H 60 TO •H ra TO TO ft 9 ft P C D TO CS P C D TO PS p ra TO PS 60 TO •r-4 C D 146 f-4 C O Q) > 9 vft 00 CM o CM to tO © o p p K -H W P I I b «* tn £ © ©

CO P £3 P £3 *H £} CO © p £ bp o •rl O *H Eh © ra ,n o c- 00 to S? in t- CM CM o Size of Nesting Territories P t*« CO to I I in in © rH o <1-1 >i o o ffl bO to p © -tH P P CQ TO © 53 bfl P *H tJ .H •rt P ,0 P TO © JS p •H •P rH •i—f P rH ,Q •H P £> •s p o h 1 ,P m O rH p in Pi P bO 5 P P p o o >> *H P to © p *r-4 P rp o © p © M *rH o O t>> *—1 CO I to tn CO 1 to in CM I tO in 147 © © to © Ph © o ra -a; © •rH o © O P h r~l © © Eh <£ El © to o o XJ o © •rl -rH X J & © CM o o C" CO O CM CO CM cc o tO 8 CM CM CM CO S o © •rH CO o El o p p O CM CQ o- >> o to © © o © © © CO o CO CO ra © o • r H S ’ •i— i E h ‘H - p 0) d © •m p © o o CO © rO © Eh rH ra <© © o o tH © P © © •2 >■ 3 © Js; ra x> o D- LO o CM CM 5> o ■tH O t o O I © © © I —I o <© >> o o © CsD tifl © © p P m CO © is ra p r-t •rH ©O'© X> W H %l g> W o 3 © O XJ >> p w >» © © o »© p © © © Cm P w 1? bD o 3) © -M O XJ Jj >> ra p *H bO r— H r*i © X> © • rH © o P p © ro •r H © & © > K) © •H -© © © P*H © o •rl P © x» d o © M ra H © d PH nd © P to © in a t to to 1 to to tn to tO -ti* CM 1 to tn CO rH \ £>in 148 O rH O to oa 02 CVJ to ■rH Nesting Sites of the Robin O CO to o o cn to rH cn CM ■P P -H 02 to to to 02 -«-C -H -P r-t o rH ■P O P. O •H 149 rH O 00 Table 03 i—I rH O 03 o o —I CO 03 9 (continued) CO 03 to o o rH o CO I CO ■H Cm O ■rH •tJ rH P. O o rH o 150 +» o o •rH o o O'* 9 (continued) 03 O Table rH -P •H i—I o rH 151 -P M Fh in £ 03 © & d © O to cn Cd r H O rH «J © •a ib p o W tEj o CO in 03 IN Fh © tn CO o o IN rH €0 -tH rH cn 00 cn o o CO o o Ph Fh © JO tn a to cn in rH 03 02 o to S3 P Nest Sites Used For First and Later Nestings tO Cl © o Fh © o CO • H to 03 IN in o o 03 cn P h to 03 cn 02 02 o o tO 03 03 S in CO CO -P d *3) u d n © o Fh © cn IN a to in 03 02 CO rH O O IN P h 05 P P •H Ph Fh © CO co 03 © © w © P ■rH p •rH © © P •H CO © d © © & & s p © © JZ5 © © © p ro d o d © jo d O © •© •°s •2 © © © P ■ 3 •H O •rH © Fh © p *H P & d o d d p p Fh Fh •rH Fh •H •in ft* © Ph © ra © p p ra © d & d • d H t o <— i cd •rH d Fh t © •rH P © 'd * d d © *3 p o E-t Fh © P 3 © P © © d Fh © P © P) O H • d Fh © d O d ra © © © d © o H p d © © © d © © & © © rH *» M OJ r H O rH cd < D JCJ & -P O tH fH ■p d rH rH o• o o 1 —1 rH CD fH cd ca rH • in u ,Q Ea d S3 o I • o -P a © •a o• CN tn 03 IN in CO • CM rH • in CD rH • 03 tO o ■ t j * rH 03 • £N CQ o• CO H* rH • 03 CO CM in o rH CD Ph U © ,Q CN H< SS ■ t4 O m d , n C O p d CD O F h ffi Ph CM O • o o rH •P +3 • H PH Fh © 'fj CO CO O rH 55 to © -p •rH TO CD •P H CO •P CO CD 53 CO a © © Fh bC Fh © © a *H CD +3 to © d CO d 8 cd © cn 01 CO d & o d •rH 01 o © 'd d cd d P TO © © Fh CD P © 03 -P d rH ad o *rH o• o in in • in • rH rH CO rH CO ■—i i o lO tn in • CD O • o CO rH rH 1 C- i> rH 1 t> *? tn tn t£> CD c- £> ss a S a> O iH O rH C0e-0-H ra © d -rH TO © xl o © © d *r-i M ■H © -p ra d © >1 fH 00 d © d o p« d 'd © © © X to © • H O © © © 1-1 w rH © ra d © o Ck © o d © © X & d o © rH fH en f&t fdt ID O ID to cr> f t to CO o co f t to co ft ft ft co ^ to co in oo co to to ft o co o- «r> co CO 00 o o O- cO o ID —1o o to ft ID i CO ft ft ft ft i—Io> to X cd & to p 03 03 « d 03 P 03 CD d cn ft d o a o ft 3 ft © 'S 03 (=1 03 ^5 3 CO p ■a •r-4 a) i cd ft d d O •H ® © © d © d p d o d o p tip d o d o X CO ►-1 P-4 d £ 03 d d 03 a3 i—I in r-j 03 ad © Pi w P-. o P +> -p © .P © fcQ CO rl cn w CM CO cr> CT> in in tO i—t in co rH W -4~> © +> *«H ■8 w fH rH © © 5 © Pi >* ■P -ri O S3 Pi >> +» o •H -p rH rH rH CVI © © © © © © © © a 3 3 © •i-4 to © ps r© •P W © P +» co © iy to w i m in o in i s * co CV2 I in in t to in CO 1 to in CO 1 to in a i to CO fl o o © M o• H o © © © N ® H n m o co © h «o H H % O p o o• CO 89 CO to to • CO o o • to 44 03 ID• to CO to to P 00 •© O J25 to 03 ft r> Monthly is; to o rH 03 • ft *0 ID q id © cn i|H rH S ta 3 t! a} © © © « p jq +o» a> 0 M © rH *rl s o n o » © a © >-» § 03 t"» ID 'H* sj* cr> © p o IH 162 a ■rH *r| P d © to to © lO CO cm IV IV tO cm in £> rH CO rH CO CO P O P p *h © « t-t a a -rl HH P h a w p TO I I I I d TO © CM rH co in o ^ ^ CM cm cn cr> O in iv Cv CM tO to to to r£S 13 S3 p. < CO o o o CM CM CM rH I I o P h Bobins d © d O o •H P ■rl to s p in in co ■*# cm CM v- in < H CM zv © p © © «'-'< t?o u • 03 © &4 d QiO © e — t> © of B e h a v io r I I I I Vi O © © rrt © d O P © *rl 0 p u d © p < Ph 3 A t t e n t iv e t o u PH Female During In c u b a tio n © «3 aH t in in to o tv tv CM u © © E •rl TO JD Eh O P. in rH O I I • PH P iv CM in o o CM CO o (—t o in to o CO to P in r— I CM rH I O O p in co co i r- 4 CM ■—I I o CTi TP rH I in co rH d o ■rl Vt 4©3 O l> u © © p m © ,JQ o o CO i>> r*> © IS © 13 to cs ss $ CO CO CO & a © >> © CO N rH 3 K in rH 3 t“3 o rH >> Ha Pi O P CO © !Si I I rH to CO in t t in t 5? in in I s 35 in t 163 • > ^ d to draw © *cJ © 4» -P fOH 42 3 fH D- 03 ts «4< c- m cD d S © *rt H fL, S d rt E o> © to © © CO O O rH O S3 s £ d ■rH E • 02 co Tf« iH I I I I rH © d H t t4 ra ra c CJ O 4* © o c d in 02 to CO cdj E h d o •H 4* 13 g 8 © &4 S *8 to a PH o o »« H < to OI in in to I in rH CO in 02 co I o a Ph 02 o rH I O 02 •« I O 02 d o rl 4» V< © ° £ © © 4-3 03 o rH © b d .O to H d b Sb © S3 & a n © 4©* © « to 02 I tn in to 03 I in in 03 I CD in CD I IN tn CO iH « Cm © tf) d u © > < 164 CD fctD CO cd M O in • CT> fc> O o • m 02 CQ O fi 02 • in 02 I 1 i O • o 1 02 • H< • O in in ■—i at rH 02 t£ > CO in 02 02 CO CO 1 • • i— 1 1 — 1 02 02 in 02 CO 02 cr> 02 • o at in • o at <— I rH 02 02 02 ■ — 1 rH CO O CO i— o in • • H 1 • rH 01 p p iH an • a bO O H* cd W Pi CD > the Nestling Period < rH C- • 02 o • tn • 02 CO • in O • 02 in • CO rH U O • • iH rH rH 1 • P h -p o 02 •H CO CO o t—1 tO CO 02 rH rH rH i— I o- in 02 rH o 02 o O o 02 CO at £> 02 O O CO i— 1 o to CO O CO 02 o o rH rH CO r— 1 02 rH 02 CO o E-« • CO Attentive • S3 • <*: m r— l •* i— 1 i—I 1 to rH «* o rH i— I I V O i— 1 02 • fH t£> in •• tO l o o •* CO CO 1— 1 4 p-i CO o •• I— I 1 in •* 02 i— 1 rH t> » Hi f5 "* cd £5 rH o- 3 •P 02 CD K 1 02 in C V2 rH 02 »H • • «H rH to 1 a S>> cd S3 CO ( in • fL, o 02 •< 02 i—1 1 to CO •• o 1 — 1 • • Pu Pn o in 1 in in •• in 02 •• CO 1 00 o •• •* 02 1 cr> 02 •• 02 e'­ rH rH •• rH r— 1 • ♦ H P* •• r— I 1 to o ** 1— I 4 pm o at rH rH i— I ■* rH 1 in h* »• 02 *— I H < o « 4 Ph • < 0- •• < — 1 i— t I o 02 O in •• 02 1 tO H* *• co •• o 1 — 1 1 in i— t o fH CD tO 02 02 m• •• *H 02 02 en 02 02 rH rH 02 in 02 rH P Hi ri rH n Hj (D g Hi i i— 1 P Hi Hi Hi Hi in in in in at t s •St* 1 i t a in to 02 1 m in CO 02 1 tn in to 02 CO 02 t in in o i— 1 t> » rH P Hi <— 1 02 :>» *3 m >> i — i t in in in 1 in in 165 to o to o cm tO cm •p H o o* © m > © ■p io to i"H ■H Table 19 (continued) in cr> to to CM to o E-* S3 8 m rH •H CD tn o to in CM to **H to O *P CM CM ■P CM tn to •P 166 S §^ ts, O © O J3 W W Fh © m u J» © © < O C4 © o Eh (3 © •P © w © CT> • 03 CO• 1 —1 CO r-H CO 03 rH to CO O r—I O CO O in O LO O O to o o rH rH CO rH O O rH r-H CO O O O o o O i co to CO CO co • a• • • a• a• • a• < << o c•o• rH • ■ © § © Cm © © o M © rH © a -p M © ss; •H © ■P O EH o £ © CO rH -K> © ■p © © rH f oH w w © a m bO © Oh •H O rH -P © CO bp © ra >> © © •rH © O *H *«H O +» © > (—1 •• 1—1 rH W in o 1 © in F-i © O o• © o © © •rH H-> ra -P © n © P» o t> i—i o © co o•• 1 —11 in 03 — 1 rH i 03 rH rH S>> © a I 03 co i $ in pH in 03 •• C O1 CO o e'­ o rH ■ in ■—i •* ■—1 I co o rH CT> rH rH en tO to 03 03 ;>» © © © 03 © Hi rH -p w • Pt • 3 Hi in t $ Hj co 03 I in in © £ O J© o © © Hi CO 03 I in in © -p o Eh 167 +3 CO CO Hz) JU o o u PQ o © fc* d © p H i n hz) d o o 03 *rH 0 taw © HZ) (Q 'd d ff| H CO a § 5 © 6D HZ) o HZ) o © d rH CO 03 CO CO H CO >■> *H d PQ C*< Hs 1 P CO © d i— 1 © •H f t d © £ Broods Between Interval F*4 B HZ) d o o © PQ o CO a i—I 60 •2 © d co Ip t» o d 60 Td © 'd O d P © o o •H d rH d M Pt< pa P -p © u O o ra i» cd O in CO d p ra © P © *r3 © © T3 rH £ o o © w & g o d o p o © o © © . S3 CD rd © ©3 ttD O TJ o © d rH pn h CO 03 t>> cd S3 »H 3 CO I s in t>> © Hj S3 rH 1 to 03 ■ * o IN 03 © in in in in cO cO in 9* d d 03 03 o- in i rH ■— i >> © a >> © S }>> © >> © S 03 rH | 010 in in OJ • V in in I S? to tn P** otf a c n 1 1 i— 03 rH 03 .H | 1 O in IN «H © S3 «H i—1 ■ i IN HZ) © in >> o p d CO *r~~i P © o o kA © 03 03 (H to CO 60 © © d < © © © © © © © © d 3 a H <5 © © > © Td p ra © j? 168 o to Fledglings rH rH in CM O CO CT» CO Behavior by Male to o Attentive CM i —I in CM o in to in in in tn in o in co -p c, < w n3 m (D i—I o in o O 05 pu in in in -p in 169 ♦4 CT > * 3 -P cd © *© o o s ■H m *© © o o +> CO © a 02 to to in CO o 03 to CO © W CO -p Cj © O 03 © -p S! © b © © O E-< ■P K W © © © 170 P C] GO Q> GO O CO in S! to in w CO £4 o> cr» cr> i— l i— I rH cr> rH (H (D in in o O o CM CQ o U o to c m CM in CD in CM iS cd Pt bO c3 cd nd CD U to CM 03 CM CO Pi ■i~l P CO CD K d o •H 03 -P U (D G> Q (M CT3 ■—I CD o in 03 rH in 03 rH in in 03 ■—i CM to tn 03 l —i ■3 t-( to § ,cJ bit) a ,ci bO S xi P P P p p P P Pi Pi *ri ■rl p a a> B n CO o bD P CD p o &H

to cd 11 o> 12 12 03. 02 81.8 Total Nests to• to in 16 CD o Total t-1 0 CD 01 CO CO 2 o 3 ■H © © Q 11 to Per Cent Successful Per Cent Successful 66.7 Success­ ful -P a Success­ ful •r~i Total Nests Per Cent Successful •H O •H Success­ ful to Sites CO i— 1 cd Total Nests Conifers in First Nests According CQ CD 4-s i-l 0*0 Success 172 o• to to co o CO rH 02 o. CO 03 in O• in bO rt 03 d 3 jc e d 3-U©0 p e T *o *B H ©i Nesting X n je e s o o n g eq.s©£i q.u©o to CM to s2 Sa cr> CM CM CM ■ — i tn CM essa: ID Dto tO to to **©£ o . vO - p n js s © o o n s s q .9 © ^ rH CO in . cri in J^d . Data pt 1— 1 X . rH CS 74.4 p© qoq.© H iH CM cn 86.1 p© 2 p©X ,2 t> CO • © A jq .o v to . CM o 00 CO o. o to to to * C-* o 1— 1 CM rH iH H o 3 in in in to in 1— 1 69.3 ugq CO . i— 1 CO • CM in . to in 79 ^ 9 CM • O- 70.8 jo to . 114 e § u x x q .B © M o. to 161 Je<£ 68.1 p e S p © -^ S u fo n p q .u e o 33 jo 47 J.& s 2 S % t> lO *• 4* to LO «k in 60 3 vH >-» ■a4 a § & ra ■8 ra ra * H (h a* r a r« C O i-i 43 w p JO m p *p «H fit p p •rH P P Total s 3 u t-[2 p 0 X ,i -o 49.1 173 Comparison of Nesting PTBl s22a Xnjsseoong q.tr©o i© in in to r-l i—i IN CO CM to cr* in CM ’tP cn to I> tn 5 to CO to 00 o CO to to CO I— I C" CM to CM rH r-l i— i g s s to CM in CM to to to tn in cr> rH m c ■a -p ® e»o g 47.1 1.3 CM CM C- 77.7 o in 456 to • E'­ CO CT> ©OU0J18J9H i 60.6 Data p©2p©X,i p©qoij.©H sS2S o> 587 to JO 3.UGO J19& J©d CO CO p©2p©x^[ s2trxiq.s©M p©qoq.©H ■tf* CM 968 in CM 54.6 o CM 196 tO sSujx^PQItS Stixonpoj^ s32& Jo q.n©o JC©d; to 359 q.S©iI 9AXQ.0V ^©d p©9p©Xi .iequrntf ©gBjceAV CT» * i-4 a ra 3 »-? ra -p ■h >» • a % -P & ra & ra ra * p •p H •H Total 1J.SO& xnjsseoong jed psSpeXJ aeqranjj gSbjoav 2.3 174 175 aJ 43 o Sri O CM tO i—I rH CM to ID 3 o o 'Ct © Pi © ra © O o O to o rH Pi o +> ra 'Cf © u Pm tO O to a cm pi Eggs ra t> Pi ra ra tO H* CM of Robin p o n=J i —I t3 Pi +©3 < ra ra Fate rH to O in CM r—i in CM Pt O raJ © H4 cd ra Pi Pi ra ra CM ■M1 in CM c- in in g O i—) H1 in in in to to in ra o E4 CO o • o o 1—1 CO O u d © d p •d • I-1 CM tn ■ t f • in op P <; Jh J§ p cd © fs to CO rH • CM CM