ABSTRACT

THE EFFECTS OF THE ENVIRONMENT ON GROWTH,
DEVELOPMENT, AND TEMPERATURE REGULATION
IN NESTLING EASTERN PHOEBES

by Harold D. Mahan

Between 1958 and 1962 nestlings and the nesting

environments of the Eastern Phoebe, Sayornis phoebe, were

 

studied in Isabella County, Michigan, to determine if there
was any correlation between growth and development of tem-
perature regulation in the nestlings and the environmental
factors present in the foraging areas of the adults.

Daily growth measurements were obtained of 25 first-
brood young, 1 to 12 days old and 21 first—brood young, 12
to 14 days old. Thirteen second-brood young, 1 to 12 days
old and 10 second-brood young, 12 to 14 days old were also
measured. Growth measurements indicated significant growth
differences in first- and second-brood young but no differ-
ence in their fledging sizes. Although no significant dif—
ference in fledging success for either brood group was
discovered, there was an average fledging time difference
of 2.1 days, with the first-brood young fledging earliest
at 14.8 days. Measurements of ectOparasite (mite) popu—1
lations on the young showed a very significant difference
in the numbers recorded on the two brood groups. The second-
brood nestlings were heavily parasitized (20 or more mites/

young) throughout their nestling lives whereas the

Harold D. Mahan

first—brood nestlings were heavily parasitized only after
nine days of age.

From the same nestling pOpulation, 15 (1—14 day old)
first—brood and 10 (1-14 day old) second-brood young were
subjected to controlled temperature chambers for two hours
(10°C. and 40°C.) in the laboratory. Body temperature
records, breathing movement counts, and general observations
of the behavioral reSponses of the young indicated that
there was a significant difference between the ability of
first- and second-brood young to control their body temper-
atures. A11 evidence indicated, however, that effective
body temperature control was established in this species
by 10 days of age. Prior to this age the young exhibited
the poikilothermic condition.

One-half hour controlled temperature environment
exposures (10°C., 25°C., 40°C.) in the laboratory of 12
first— and 17 second—brood one to six day old young showed
no significant difference in the gaping reSponse ability
between either brood group. There was, however, a signifi—
cant difference in the number of gaping responses among
each brood group at each of the three environmental temper—
atures investigated, indicating that air temperature
directly affects the gaping response ability of the young.

The growth measurements and laboratory investigation
of body temperature control indicated, therefore, that there

was a significant difference in the growth and development

Harold D. Mahan

of temperature regulation in the first— and second-broods
in this species, possibly caused by increased ectOparasite
populations on the second—brood young. This difference was
not reflected, however, in the ability of the young between
one and six days of age to respond by gaping to mechanical
stimulation after short periods of controlled temperature
exposure. Apparently, however, the ability of all young

to gape was affected by extreme air temperatures in that
the greatest number of gaping responses was recorded after
exposure to the 25°C. environments.

Environmental data were collected at three first-
brood and three second-brood nests during the first 12 days
of nestling life. One first—brood nest contained four
young. The number of young was reduced to two in all other
nests.

The size and nature of the adults' foraging areas were
analyzed at all nests. The size of all foraging areas aver-
aged 4,727 square meters. The most pronounced changes in
foraging area size were recorded during adverse weather con-
ditions (high winds and/or heavy rain).

Daily weather conditions (air temperature, wind speed,
sky cover, rainfall, relative humidity) were continuously
recorded in the foraging areas, as were the density and
weight of aerial arthrOpods present (presumably available

for feeding the young).

Harold D. Mahan

Although there were seasonal fluctuations in the num—
ber and Species of aerial arthrOpods present, the majority
belonged to seven arthrOpod groups. The arthropods collected
indicated strong correlations between their number and weight
and the existing weather conditions. The feeding activities
(number of trips to the nests presumably with food) and
brooding behavior of the adult phoebes likewise indicated
strong correlations with the existing weather conditions.

Correlation coefficients of the daily weight gain of
the young and weather conditions indicated little relation-
ship between these factors, however. Similarly there were
slight negative correlations between the daily weight gain
of the young and the number of available arthrOpods in the
foraging areas of the adults as well as the number of trips
that the adults made to the nest. The slight negative char-
acter of these correlations, in fact, suggested that an in-
crease in the number of arthrOpods present and an increase
in the number of trips to the nest by the adults were
reflected in a decrease in the weight gain in the young.
Possibly this indicates that the changing nature of the
arthrOpods present during adverse weather conditions
together with a changing foraging pattern by the adults
resulted in fewer but possibly larger arthrOpods being cap-
tured, and therefore of greater weight-gain value to the
young. This also would result in fewer trips to the nest

during such weather. Possibly, also, the poikilothermic

Harold D. Mahan

condition of the young aided in less weight loss during
adverse weather periods due to lowered activity. Probably,
too, there were other factors Operating. In any case, no
environmental factor appeared to be so detrimental to the
young in this species as to inhibit successful fledging.
Otherwise, the Eastern Phoebe would not be as successful

as it is in the areas where it now nests.

THE EFFECTS OF THE ENVIRONMENT ON GROWTH,
DEVELOPMENT, AND TEMPERATURE REGULATION

IN NESTLING EASTERN PHOEBES
By

Harold D. Mahan

A THESIS
Submitted to
Michigan State University

in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Zoology
1964

ACKNOWLEDGMENTS

Many people have aided me in the design, execution,
and preparation of this investigation, and to all I am
very grateful. I am especially grateful to Dr. George J.
Wallace for his kind advice, understanding, and encourage-
ment during each stage of the research and the final
preparation of the data.

‘Drs. James A. Braddock, M. Max Hensley, and Gordon
Guyer all gave valuable suggestions and read and corrected
the entire manuscript. To Drs. Phillip Clark and Jack
Adams I wish to express my appreciation for statistical
help and for valuable comments on the final arrangement of
the data.

To Dr. Michael Carson of Central Michigan University,
and to George Pellerin, Earl Peck, Janet Ellithorpe,

Marian Clark, and Donna Butcher, students at Central Michi—
gan University, I am indebted for assistance in the
laboratory and field.

It would be grossly unfair not to include two men who
constantly encouraged me during my early education and in
all stages of this investigation. To Walter P. Nickell of
the Cranbrook Institute of Science, and to Dr. Nicholas L.
Cuthbert of Central Michigan University I shall always be
grateful.

ii

The final stages of the research were made possible
through a National Science Foundation Faculty Fellowship
(NSF #64013), without which the project could not have been
completed.

Finally, grateful acknowledgment is extended to my
wife, Mary. Without her constant interest, encouragement,
consideration, and assistance this manuscript would still

be unfinished.

iii

CURRICULUM VITAE

Harold Dean Mahan
candidate for the degree of

Doctor of Philosophy
Final Examination: May 14, 1964

Dissertation: The Effects of the Environment on Growth,
Development, and Temperature Regulation
in Nestling Eastern Phoebes.

Outline of Studies:

Major subject: Zoology
Minor subject: Entomology

Biographical Items:
Born: June 11, 1931, Ferndale, Michigan.

Undergraduate Studies: Wayne University 1950—1954,
Arizona State College 1951, Phoenix City College
1952.

Graduate Studies: University of Michigan (M. S.
degree) 1955—1957, Michigan State University,
1958-1964.

Experience: Non-commissioner Officer, United States
Air Force 1950-1952; Instructor and Assistance
Professor of Biology, Central Michigan University
.1957-1964; National Science Foundation Faculty
Fellow 1962-1963.

Professional Memberships: Society of Sigma Xi, Phi
Sigma Society, Phi Kappa Phi, Beta Beta Beta, Phi
Delta Kappa, American Ornithological Union; Wilson
Ornithological Society, Michigan Academy of Science,
Arts, and Letters.

iv

TABLE OF CONTENTS

Page
ACKNOWLEDGMENTS . . . . . . . . . . . . . ii
'VITAE . . . . . . . . . . . . . . . . iv
LIST OF TABLES . . . . . . . . . . . . . vii
LIST OF GRAPHS . . . . . . . . . . . . . ix
LIST OF FIGURES . . . . . . . . . . . . . x
LIST OF PLATES . . . . . . . . . . . . . xi
SECTIONS
INTRODUCTION. . . . . . . . . . . . . 1
MATERIALS AND METHODS. . . . . . . . . . 5
RESULTS . . . . . . . . . . . . . . 21
Growth of Nestlings . . . . . . . . . 22
Weight. . . . . . . . . . . . . 22
Length. . . . . . . . . . . . 23
Feather Growth . . . . . . . . . . 23
Fledging of Nestlings. . . . . 26
Growth of EctOparaSite POpulations on
Nestlings . . . . . . . . . . 26
Cowbird Parasitism. . . . . 27
Development of Temperature Regulation in
Nestlings . . . . . . . . 27
Internal Body Temperature . . . . . . 27
Breathing Movements . . 29
ReSponses of Young After Two— hour Exposures
to Controlled Temperature Environments. . 3O
ReSponses of Young After One-half Hour
Exposures to Controlled Temperature
Environments . . . . . . 30
Study of the Nestling' 8 Environment . . . 31
Size and General Nature of Foraging Areas . 31
Weather Conditions in Foraging Areas. . . 33
Kinds and Densities of ArthrOpods in
Foraging Areas. . . . . . . 36

Section

Feeding Behavior
Brooding Behavior.
Nest Desertion. . .

Development and Activities of the NeStlingS
Growth . .
Deve10pment of Behavior in the Nest.
Pledging. . . . . . .

DISCUSSION AND CONCLUSIONS
SUMMARY.

LITERATURE CITED.

vi

Table

IO.

11.

LIST OF TABLES

Page

Summary of mean growth measurements: 1 to 14
day old first-brood Eastern Phoebes . . . 80

Summary of mean growth measurements: 1 to 14
day old second-brood Eastern Phoebes. . . 81

Summary of temperature regulation experiments:
15 first—brood nestling Eastern Phoebes. . 82

Summary of temperature regulation experiments:
10 second—brood nestling Eastern Phoebes . 83

Gaping responses of nestling Eastern Phoebes
after one-half hour exposures to controlled
temperature environments. . . . . . . 84

Daily summary of nestling and environmental
conditions at two—young nest No. 61—16,
May 24-June 4, 1961 . . . . . . 85

Daily summary of nestling and environmental
conditions at two-young nest No. 61-16A,
July 8-19, 1961. . . . . . . . 86

Daily summary of nestling and environmental
conditions at two—young nest No. 62—17,

May 18—29, 1962. o o o o o o o o o 87

Daily summary of nestling and environmental
conditions at two-young nest No. 62-22A,
July 3-14, 1962. . . . . . . . . . 88

Daily summary of nestling and environmental
conditions at two-young nest No. 62-17B,
July 28—August 8, 1962 . . . . . . . 89

Summary of nestling and environmental condi—
tions at four—young nest No. 61-17,

June 20-July 1, 1961 90

vii

Table

12. Comparison of the nesting environments at
five 2-young nests and one 4—young nest
of the Eastern Phoebe during the first
12 days of nestling life. (Arranged in
order by nesting dates.) . . .

13. Numbers of individuals of each arthrOpod
order in the foraging areas at Six nests
of the Eastern Phoebe during the first

twelve days of nestling life (1961-1962).

viii

Page

91

92

Graph

II.

III.

IV.

LIST OF GRAPHS

Page

Number of mites found on 20 randomly selected
nestling Eastern Phoebes from first- and
second-brood nests. Each point represents
the mean number of mites on five randomly
selected nestlings during either 1959 or
1960.. . . . . . . . . . 94

Mean difference in number of breaths per minute
between 10° C. and 40° C. two hour controlled
temperature exposures for 15 first—brood and
10 second-brood young . . . . . . . . 96

The relationship between mean daily number of
insects and weather conditions in foraging
areas of 2-young broods of the Eastern Phoebe.
(Each point represents the mean values for
the first 12 days of nestling life at each
nest.) . . . .. . . . . .. 98

The relationship between mean number of trips to
the nest daily, brooding behavior daily, and
daily environmental conditions in foraging
areas of 2-young broods of the Eastern Phoebe.
(Each point represents the mean values for the
first 12 days of nestling life at each nest.). 99

The relationship between daily weight gain of 2—
young broods of the Eastern Phoebe, adult
attentiveness, and environmental factors. (Each
point represents the mean values for the first
12 days of nestling life at each nest.). . . 101

ix

Figure

LIST OF FIGURES

1. Diagram of temperature control chamber in
cold cabinet with air source, manometer,

and position of nest and young in chamber.

2. Method used to determine unknown area Size
of adult Eastern Phoebe foraging areas.

2A.

2B.

Map of foraging area (reduced to

1/5 actual size) of adult Eastern
Phoebes at nest Site No. 22 during
1961 and 1962, showing quadrat
subdivisions for random sampling
insect pOpulations. Map is drawn

to scale (each quadrat equals 10 sq.
meters) on larger rectangle of
known area size.

Map removed from larger rectangle
for weighing. The proportion be-
tween weight of rectangle paper and
the square area that it represents
equals the proportion between the
weight of the same map removed from
the Same rectangle and its (unknown)
size.

Page

103

105

LIST OF PLATES
Plate Page

1. Field weighing kit with Ohaus triple-beam
balance and plastic container for weigh-
ing young older than nine days. . . . . 107

2. Field Tabulation Forms for recording and
tabulating growth measurements of young
(reduced 4/5) . . . . . . . . . . 109
2A. Daily field record.

2B. Growth measurement tabulation form.

3.. Standardized Laboratory and Field Forms
(reduced 4/5) . . . . . . . . . 111

3A. Temperature Regulation Experiment
Form.

3B. Field Compilation Form
4. Wind-vane type arthropod sampling instrument . 113
4A. Arthropod sampling board mounted on
top of 6' metal pole.
4B. Close- up of masonite board containing
"tree- tanglefoot” for trapping
arthropods.
4C. Carrying case for masonite boards.
5. Trip recorder for recording the number and
duration of adult trips to the nest during
feeding hours . . . . . . . . . . 115

5A. Hand-wound clock recorder opened
to Show trip-record paper in place.

5B. Recorder closed during recording
period.

xi

Plates Page

6. Nestling platform cage with micro-switch
perch with electric lines going to
trip recorder . . . . . . . . . . 117

6A. Nesting platform cage in place prior
to enclosing nest.

6B. Nesting platform cage in use. Note
that micro-switch perch is even with
nest rim.

7. Four-hour cycle contact sensitive paper for
recording trips to the nest by adults at
Nest No. 62-17B on July 28,1962 between
8:10 a.m. and 12:00 p. m. (33 tri s) and
between 4:00 p.m. and 7:50 p. m. €46 trips). 119

8. Artificial nestling used in an attempt to
collect food brought to the nest by the
adults . . . . . . . . . . . 121

8A. Head of artificial nestling with
metal "mandibles” partly open,
mounted on end of a tube of stiff
muslin.

8B. Artificial nestling with mandibles
closed, enclosed by nest on nesting
platform.

80. Front of nest platform showing
arrangement of micro-switch perch.
Two six—volt batteries are attached
below.

9. Recorder arrangement for continuously measur-
ing the temperatures at the bottom of the
nests . . . . . . . . . . . . . 123

9A. YSI laboratory recorder with dials set
in standardized fixed positions.

9B. YSI laboratory recorder and 12 volt
automobile battery power source. Note
wheatstone bridge arrangement in cir-
cuit with two, 6 volt batteries to the
left of the recorder. The D.C. to A.C.
converter is above YSI recorder.

xii

Plate

10.

11.

12.

13.

14.

15.

16.

17.

18.

Page

Nest temperature records at Nest No. 62-
17B on July 28, 1962, recorded on YSI
Laboratory Recorder contact-sensitive
paper which moved at the rate of one
inch per hour. Note the scale of
temperature values at the top of the
left chart segment . . . . . . . . . 125

Instrument and observation tent at Nest No.

22A (circled with arrow). Note electric

lines to nest and insect sampling board

at far right . . . . . . . . . . . 127
Hygrothermograph for obtaining 24 hour con-

tinuous records of air temperature (0 C. )

and relative humidity in the foraging

areas of the adults. . . . . . . . 127

Hygrothermograph record at Nest 62-17B on
July 28, 1962. . . . . . . . . . . 129

Growth photos of one .day old nestling Eastern
Phoebes. . . . . . . . . . 131

14A. Side View
14B. Ventral view
Growth photos of 3 day old nestling Eastern
Phoebes. . . . . . . . . . 131
15A.. Side view
15B. Ventral view

Growth photos of 5 day old nestling Eastern
Phoebes. . . . . . . . . . . . 133

16A. Side view
16B. Ventral view

Growth photos oflIDday old nestling Eastern '
Phoebes. ,. . . . . . . . . 133

17A. Side view
17B. Ventral view

Growth photos of 15 day old nestling Eastern
Phoebes. . . . . . . . . . . . 135

18A. Side View

18B. Ventral view
xiii

INTRODUCTION

During the past 25 years considerable attention has
been given to the relationships between the energy exchanges
of organisms and their enviornments. Although relatively
little attention has been paid to the higher vertebrate
groups, a number of ornithologists (notably Koskimies, 1950;
Lack, 1952; and Udvardy, 1953 in Europe; and, in this
country, Baldwin and Kendeigh, 1932; Barthelomew, and
Dawson, 1958; Dawson, 1954; Dawson and Evans, 1957, 1960;
Farner, 1956, 1958; Kendeigh, 1952; and Scholander, 1955)
have attempted to determine the bioenergetic relationships
of birds. Although most of these studies have shown the
physiological adjustments that birds can make, few studies
have attempted to relate these adjustments to the total
nesting Situation of the species. Although the great
mobility of birds prohibits a complete investigation,
there are certain periods in their lives when energy-
exchange relationships may be studied fairly easily.

With altricial birds, the period when the young are
still confined to the nest is an excellent time to deter-
mine these relationships. At this stage the young bird's
ecosystem has definite limits (i.e., the area in and
around the nest, including the feeding area of the adults).

1

To relate the adjustments that occur between the young and
the ecosystem, one can choose a Single factor that repre-
sents the growth of the young and relate the development
of this factor to the elements in the environment that

are affecting it. With altricial birds, one such factor
is internal temperature regulation, and because of its
great importance in the growth of young birds, it was
chosen as a focal point for this investigation.

In general, altricial birds hatch in a very under-
developed state, and consequently have little ability to
maintain a constant body temperature in extreme ambient
temperatures. AS these young are fed they increase in
mass, grow an insulating covering of feathers, and
develop internally in such a way as to become increasingly
homoiothermic. Their ability to regulate internal temper-
atures, then, is related to their development and must
also be related to environmental factors controlling
growth. The major factor in the environment that controls
their growth is the abundance and availability of food.

In the case of birds that feed on flying insects,
food supply is controlled primarily by the physical
factors in the environment. The studies of Glick (1939)
and Palmen (1944) have shown that the density and
activity of flying insects is primarily controlled by
the weather. If this is true, it seems logical to assume

that there is a relationship between the growth of the

young of aerial—feeding birds and the weather, and perhaps
other ecological factors that are affecting their food
supply. Furthermore, it Should follow that if the develop-
ment of body temperature control is dependent upon growth,
that both this and the factors controlling availability of
food are likewise related. To date, no study has Shown

the degree to which these factors are related for any
passerine Species, and it is the purpose of this investi-
gation to do so.

During the Spring of 1958 a study was begun in
Isabella County, Michigan, to determine the relationship
between the environment and the development of growth and
temperature regulation in the young of the Eastern Phoebe,

Sayornis phoebe Latham. At the beginning of this investi-

 

gation an attempt was made to study the growth of the

young and to correlate this with the development of their
thermoregulatory ability. Subsequently, the environment of
the young of this species was analyzed to determine (1)

the amount of potential food available to the adults for
feeding the young, (2) the factors in the environment
controlling the availability of this food, (3) the amount
of food actually fed the young, and (4) other factors in
the environment that were affecting the growth and devel-

Opment of the young.

The Eastern Phoebe was chosen for this investigation
for several reasons: it is a common summer resident in
Isabella County, Michigan (Cuthbert, 1962); it is a Species
which feeds exclusively on arthropods during the nesting
season (Merry, 1941); and its nesting situation easily
lends itself to field and laboratory investigations. In
addition, it also has been studied extensively with regards
to growth and development of the young (Stoner, 1939;
Merry, op. cit.; Wetherbee, 1957), feeding frequency of
the young (Kendeigh, 1952), and development of temperature
control in the young (Stoner, op. cit.). Another inter—
esting consideration is that this species, unlike many
perching birds, commonly raises two broods of young in
the same nest during a Single nesting season. This
second brood of young is very often heavily infested with
ectoparasites (primarily mites), and this environmental
influence is of extreme interest in connection with the
development, growth, and the development of temperature
regulation in the young. Finally, of great Significance,
is the long nesting period, which in the study area
extends from April until August and provides a wide
variety of weather and environmental conditions under which

this species can be studied.

MATERIALS AND METHODS

In general it was necessary to make three separate approaches
simultaneously in this investigation. The first involved determining
the general growth and development of the young; the second, the determination
of the thermoregulatory abilities of the young; the third, the ecological
factors controlling the growth of the young.

Growth rates were determined by obtaining daily weights and various
linear measurements in the field. These were obtained each evening
at 7:00 p.m. (t. 30 minutes).

Daily weight measurements were obtained with an Ohaus triplebeam
balance, accurate to 0.1 grams. This instrument was securely attached
to the bottom of a wooden box. The cover of this was designed so as to
serve as a windbreak. Two levels were mounted on the box so that the
balance could be maintained in a level position. Very young nestlings
were weighed on the open pan. Due to increased movements, however, it
was necessary to place young older than nine days in an open plastic
container before weighing (Plate 1).

Measurements of length were obtained with steel calipers in
conjunction with a steel millimeter-graduated rule. The following
measurements were made:

(1) total body length, from the tip of the bill to the

posterior end of the coccyx.

(10)

(ll)

(12)

(13)

0\

length of the right third down feather from the
posterior end of the dorsal tract,

length of the right third down feather from the
posterior end of the ventral tract,

length of the innermost down feather on the inner
wing feathers,

length of the innermcst down feather on the outer
wing feathers,

length of the innermost tail feather down,
length of quill and barb on the right third
feather from the posterior end of the dorsal
tract,

length of quill and barb on the right third
feather from the posterior end on the ventral
tract,

length of quill and barb on the right third
innermost secondary feather,

length of quill and barb on the right third
innermost greater secondary covert feather,
length of quill and barb on the right third
innermost primary feather,

length of quill and barb on the right third
innermost greater primary covert feather, and,
length of quill and barb on the right innermost

tail feather.

All other feathered areas were measured but their growth
are only briefly summarized in this investigation.

Early in the study it appeared that the rapidly
increasing numbers of ectoparasites were adversely
affecting the young in the second broods. Beginning in 1959
an attempt was made to determine the effects of ectoparasites
on the young in the first- and second-brood nests. During
1959 and 1960 five young of each day of age in first and
second broods were randomly selected from the nestling
population that was being studied. Ectoparasites were
removed from these young with a fairly stiff camel‘s hair
brush. The young were held over a flexible plastic grid
sheet and brushed vigorously along their dorsal, ventral,
alar, and caudal tracts. After the ectoparasites were
identified and counted, the plastic sheet was rolled into
the shape of a funnel and the ectoparasites were dumped
back on the young.

Although social parasitism by the Brown-headed

Cowbird (Molothrus ater) occurred in several nests, all

 

cowbird eggs were removed as soon as they were discovered
in order to eliminate this factor in the study.

All young phoebes were individually marked in a
coded fashion with a plastic lacquer so that they could
be recognized on each visit. When five days of age this
marking system was replaced with serially numbered govern-

ment bird bands.

A field tabulation form (Plate 2) was used so as to
standardize the growth measurements obtained each day.

Investigations of the thermoregulatory abilities of
the young were made in the laboratory. This was accom-
plished by removing one or two young from each nest each
evening and transporting them, in most cases, a distance
of less than three miles. Evening was chosen for these
experiments so that the young would not be deprived of a
full day of feeding. In the laboratory the birds were
placed in an empty nest for a period of one—half hour.
During this time they were also weighed, fed with a mix-
ture of dog food and mealworms (using the method of Dawson
and Evans, 1957:316), and allowed to adjust to room
temperature (2590. - 280C.). At this time they were
placed in either a controlled high- or low-temperature
environmental chamber.

The temperature controlled chambers were constructed
from unpainted one-gallon cans which had brass fittings
for incoming and outgoing air lines mounted on the lids.
The intake air line extended through the lid to three
centimeters above a phoebe nest placed on the bottom of
the can. The exhaust air line began at the very top of the
can. This arrangement assured efficient circulation of
air pumped through the chamber.

Each container was placed either in a high-tempera-

ture (100C. i .5OC.) refrigerator or a low-temperature

(400C. i .590.) incubator so that constant temperatures
within each container could be maintained. Air was pumped
from a double-piston Marco air pump through a manometer (at
a rate of 150-300 cc./min., depending upon the age of the
bird) into each chamber. Using this arrangement (see
Figure 1) it was possible to expose the nestlings to con-
stant high or low temperature environments for any time
period desired.

During the 1959 and 1960 experiments the young
phoebes were confined in the darkened chambers for a
period of two hours. AS Dawson and Evans (1957) showed
with a similar technique with the Field Sparrow, Spizella
pusilla, and the Chipping Sparrow, Spizella passerina,

a two-hour period is sufficient to allow young of passerine
species to reach a post-absorptive resting state and to
adjust as best they can to the environmental temperature.

After removal from the controlled environments, the
body temperatures of the young were measured immediately
with a fast registering small animal thermometer inserted
in the cloaca to a depth of eight millimeters. Following
this, the breathing movements were counted and recorded:
In very young nestlings exposed to cool environments the
breathing movements were so slight that they could be
detected only by observing the birds under a dissecting

microscope.

10

In order to compare the temperature regulation ability
of the young with adults of this species, five adults were
captured at nests outside the study area and subjected to
100C. and 4000. controlled environments using a technique
similar to that used with the young.

During 1960 and 1961 five young for each day of age
between one and Six days from both first- and second-brood
nests (two from first-brood nests; three from second-brood
nests) were randomly selected from the nesting population
and subjected to controlled temperature environments of
1090., 250C., and 400C. under conditions identical to the
above but for only one-half hour periods. At the end of
each of the one-half hour exposure periods in the controlled
temperature environments the lids to the containers were
quietly removed and the nests in the containers were than
jarred to determine the effects of the Shorter temperature
exposure period on the gaping response and general behavior
of the young.

In no case were the same birds used on two successive
nights in the controlled temperature experiments. After
each experimental period the birds were allowed to adjust
to room temperatures, were fed again, and then returned to
their nests, approximately three hours after removal. In
nearly 300 experiments only four young died, and there was
no noticeable difference between the growth of the experi-

mental birds and those left in the nest.

11

All laboratory measurements and observations were
recorded on a standardized tabulation form (Plate 3A).

Various techniques were used to measure the biolog—
ical and physical factors in the nesting environments
studied. Methods were developed to investigate insect
densities, feeding rates of the young, amount of food
fed to the young, nest temperatures, temperatures of the
young in the nest, and the weather conditions in the
nesting territory.

Early in the investigation an attempt was made to
determine the densities of arthrOpodS in the feeding
territory of the adults. Although many attempts have
been made to determine the densities of aerial arthropods
in various environments (Phillips, 1931; Gray and Treloar,
1933; Beall, 1935; Johnson, 1951; Craig, 1953), the
techniques first developed by Peterson (1934) and later
modified by Taylor (1960) seemed most suitable for the
present study. This technique involves using a vertical
board coated with a sticky substance mounted on a
revolving base. In this investigation a wind vane was
attached to the back of the boards so that the coated
surfaces would always face the wind (if the wind Speed was
three miles an hour or greater). The front of these
"sticky board” traps consisted of 18” X 18" X l/8th inch
white tempered masonite boards attached with metal clips

to l/8th inch aluminum sheets. Each board was mounted on

12

tOp of a five foot metal pole (Plate 4A). At the beginning
of each daily recording period (within 15 minutes of the
first actual feeding flight to the nest), the masonite
boards, coated on one side with ”tree tanglefoot" (a
commercial insect trap compound), were attached to the
masonite boards clipped to the aluminum sheets (Plate 4B).
At the end of each recording day (within 15 minutes of
the last feeding flight to the nest) the masonite boards
were removed to the laboratory in a carrying case (Plate 4C)
and the arthropods were removed with a pithing needle,
placed in xylene for five minutes to remove the trap com-
pount, air-dried on blotter paper, counted, and identified
to order. Immediately afterwards they were weighed on a
chain balance, accurate to .0001 grams.

Each arthropod sampling device was placed at a
random position in the feeding territory of the adults.
This was accomplished by mapping the foraging areas of
adults by recording the maximum feeding distances traveled
from the nest at four of the most accessible nests. These
maps were constructed during the two nesting seasons (1959,
1960) prior to the nesting seasons when the environmental
measurements were made (1961, 1962) in order to have maps
of the potential foraging areas for sampling. Next, the
foraging areas were divided into 30 or more equal-Size,
10 meter square quadrats to which numbers were assigned for

random sampling. This method is an adaption of the random

l3

sampling technique prOposed by Dice (1952) for irregular-
Shaped ecosystems. Five sampling boards were used in each
nesting territory, and in every case they were placed in
the centers of the randomly selected quadrats. The period
required for placing or removing all arthrOpod sampling
boards averaged eight minutes.

As has been already indicated, the foraging areas of
the adults were carefully mapped during the two years prior
to the actual environmental observation and measurements.

In every case this was done twice daily (5-6 a.m.; 7-8 p.m.)
every other day during the period when the young were in

the nest. During 1961 and 1962 (when the actual environ-
mental conditions were studied) the foraging areas were
again mapped in a similar fashion so as to determine (1)

the accuracy of the maps in regards to the foraging areas
for the periods when the environmental studies were

actually being made, and (2) for determining the Sizes of
the foraging areas during the same period. Since no plani-
meter was available the latter was determined by carefully
cutting the foraging area maps from the graph paper on which
they were drawn, weighing these maps on the chain balance
mentioned on page 12, and comparing their weights with the
weights of similar pieces of graph paper on which square
areas (enclosing the mapped areas) of a known unit—area size
had been drawn (See Figures 2A and 2B). This weight-

percentage comparison therefore made it possible to calculate

14

the sizes of the irregularly shaped foraging areas. This
method is an adaptation of_that suggested by N. L. Cuthbert
and used by Niergarth (1964) for analyzing the percentage
composition of different vegetative types in a marsh com—
munity.

The rate at which the young were visited by the adults
was measured with a 6—volt, battery-Operated circuit-closing
electromagnet in commection with a hand-wound clock recorder
(see Plate 5). The trigger for this recorder was a movable
perch, mounted on a micro—switch attached to a nesting shelf
containing the nest. Both Sides of the nesting Shelf were
closed with 1/4" wire mesh so that the adult had to trip the
switch when landing on the nest (see Plates 6A and 6B).

This recording arrangement is a modification of the "ito-
graph" recorder designed by Kendeigh (1952). AS the adults
landed on the perch it touched a metal plate below. This
closed the circuit in the recorder and caused the recording
stylus to mark a line on the contact sensitive paper in the
recorder (see Plate 7). The recording paper revolved on a
four-hour cycle drum. As the adult left the perch the cir-
cuit was broken and the stylus in the recorder returned to
its original position, leaving another line. In this fashion
it was possible to measure both the number of trips to the
nest and the duration of each trip, providing that the minimum
time between trips was greater than 15 seconds (in which case

only a single line would be recorded).

15

Although Kendeigh (1952) and many other investi-
gators (Betts, 1954; Fant, 1953; Greenewalt, 1955; Gurr,
1955) have used recording devices similar to the above to
determine attentive behavior of the adult birds, Betts (1955)
has suggested that such instruments do not always provide

an accurate means of determining the feeding frequency or

 

the amount of food actually brought to the nest. In order
to obtain a more accurate measurement of the amount of food
fed to the young, four approaches were made: (1) direct
observations of the adults' feeding behavior and their sub-
sequent trips to the nest with food after observed catches,
(2) direct observations of the adults actually feeding the
young at the nest, (3) the construction of an artificial
nestling to collect food from the adults, and (4) recording
the daily weight changes in the young.

Although the feeding behavior of the adults was care-
fully observed, it was usually not possible to determine how
many insects were being captured on each feeding trip.
Neither was it often possible to follow the trips to or from
the nest, due, in most cases, to the adult's activities being
obscured by dense foilage or other obstructions in the feeding
area. All observations, however, were recorded of trips
that resulted in an arthropod being captured, brought to the
nest, and fed to the young. For convenience, the catches of
such arthropods were recorded according to whether they

occurred (1) in the open air, (2) on the ground or within six

 

Ce

>.u

 

“v

'-

chi

-V‘
"oo

and

“P6

‘ .

'r
h
'-._

16

inches above the ground, and (3) among the foliage of the
vegetation in the feeding areas.

There were so few instances when it was possible to
identify by observation either the number or kinds of
arthrOpods fed to the young in the nest that this approach
was soon abandoned. (At two nests, 61-16 and 61-16A, it
was possible to observe the young from a distance of only
23 inches, but on no occasion during 26 hours of intensive
observations was it possible to identify the number or kinds
of arthrOpods being fed.)

In 1962 a dummy or artificial nestling, Similar to
that described and illustrated by Smith (1945), was con-
structed so as to provide a direct means of obtaining food
brought to the nest by the adults. This nestling was placed
in Nest 62-1 and later in Nest 62-17A. Although it did not
prove successful in either nest for obtaining feeding data,
it did illicit very interesting behavioral reactions from
the adults and for this reason it seems worthwhile to include
a description of its construction and use.

The artificial nestling was electrically controlled by
an electromagnet arm serving to pull down a thin metal plate
molded so as to resemble a lower mandible of a nestling (see
Plate 8). The upper portion of the artificial nestling was
the skin and upper mandible of a seven day old phoebe. The
inside of the nestling's mouth was painted a bright yellow

and the throat was constructed of a bright yellow denim

 

1“
D
|

 

‘Vv

‘0

L)-

‘1'.

...v

l7

cloth, rolled into the form of a tube and attached to the
bottom of the metal, lower mandible. This tube lead to a
glass jar mounted below the floor of the nest. The contact
points on the wooden perch (described on page 14) served as
a trigger for Operating both the artificial nestling's gape
and the trip recording instrument. AS the adult landed on
the perch the lower mandible opened, exposing a bright
yellow gape. As the adult left the perch the mandible re—
turned to its original closed position.

A further effort to obtain a measurement of the food
fed to the young involved obtaining daily weight changes in
the nestlings. Each young was weighed each day at 7:00 p.m.
(: 10 minutes) in the same manner as in the growth studies
carried out earlier in the investigation.

For that portion of the investigation that involved
the study of the ecological aSpectS of the feeding environ-
ment and nestling life of the young, the number of young in
all but one nest was reduced to two. This was done so as
to have comparable data at each nest. One nest was left
with its full complement of four young so as to uncover any
relationship between the number of young in a nest and the
feeding rates of the adults.

A11 young were marked with paint as soon as they
hatched and the two young nearest in age (in the two-
brood nests) were left in the nest. The remaining young

were transferred to nearby phoebe nests (and in one case to

18

a nearby nest of a Barn Swallow, Hirundo rustica, where

 

they successfully fledged with three Barn Swallow young 14
days laterl).

During the 1961 and 1962 nesting seasons nest temper—
atures were continuously recorded at the bottom of the nests
where the feeding environments and growth of the young were
being intensively studied. These temperatures were obtained
on the floor of the nests under the young. This was accom-
plished by placing on the bottom of the nest an 8000 ohm
thermistor probe in circuit with a YSI millivolt laboratory
recorder (see Plate 9A). The low sensitivity of this recorder
necessitated the placing of a wheatstone bridge in series
with the electrical circuit in order to obtain a greater
sensitivity. Using this arrangement it was possible to
convert records of electrical changes in the thermistor to
degrees of temperature on the contact-sensitive recording
paper (see Plate 10). This instrument was calibrated at the
beginning and end of each series of experiments at each nest,
and varied in its accuracy only i..5 C for all experiments
in which it was used. Two heavy duty l2-volt automobile
batteries were used, one at a time, as the power source for
the recorder. The pole wires were connected to a D.C. to
A.C. converter (see Plate 9B). Each battery was recharged
every other night so that one would always be in a charged
condition during the recording periods. The use of house

current as a power source for this instrument was, during

19

most of the recording periods, not suitable since the use
of electrical appliances, etc., along the electrical lines
occassionally affected the recording needle.

A11 recording instruments were housed with a 9' X 9'
umbrella tent which also served as a blind (see Plate 11).
This was erected two days prior to the time that records
were obtained, and in no case did its presence (within 50'
of the nest) cause the adult birds to abandon the nest.

The weather conditions in the nesting territories were
measured with a hand-held anemometer, a U. S. Weather Bureau
rain gauge, and a Bendix Hygrothermograph (Plate 12). The
clock Operated hygrothermograph gave continuous inked
records of air temperature and relative humidity for a 24
hour period (Plate 13). The Speed and direction of the wind
were measured and recorded every four hours between 4:00 a.m.
and 8:00 p.m. The light conditions (sky cover, sunshine,
etc.) were also determined at the same time. An arbitrary
coding system was used to describe the amount of light pres—
ent during the daylight hours. The amount of sky cover in
the visable horizon was the basis for this code: Sunny (S),
less than 25 per cent of the sky covered by clouds; Cloudy
(0), between 25 and 75 per cent of the Sky covered by clouds;
Overcast (0), more than 75 per cent of the sky covered by
clouds. All weather observations and measurements were
recorded on a standardized field form (see Plate 14). All

weather instruments were calibrated at the beginning of each

2O

daily recording period. In no case was the calibration
variation greater than two per cent.

If possible, all weather instruments were placed in
the center of the foraging areas of the adults as deter—
mined by using the scaled maps of these areas described on
page 12, In every case the instruments were placed in a
sheltered, portable weather cabinet, three feet above the
ground.

Detailed notes were also taken of observations made
of the activities of the young in the nest (movements, etc.)
and of the adults and their behavior. Early in the nesting
cycle at several nests(before actual nesting had commenced)
the adults were captured in mist nets, color marked, and

released.

RESULTS

The general body growth and development of 38
nestling Eastern Phoebes in 32 nests were studied between
1958 and 1961 in Isabella County, Michigan (see growth
photos: Plates 15, 16, 17, 18, and 19). Growth measure—
ments were Observed daily for 38 individuals (25 first—
brood young and 13 second-brood young) from 1 through 14
days of age, and for 31 of the same individuals (21 first-
brood young and 10 second—brood young) from 12 through 14
days of age. From the same population from which these
young were taken, 15 other first—brood and 10 other second—
brood young for each day of age, 1 through 14 days, were
subjected to controlled temperature environments of 10°C.
and 40°C. for two hour periods to determine their thermo—
regulatory abilities.

During 1960 and 1961 five young of each day of age,

1 through 6 days, were also subjected to the same controlled
temperature environments but at 10°C., 25°C., and 40°C. for
only one-half hour periods to determine the effects of these
temperatures on behavior.

Weights of 24 adult phoebes from the 1958—1962 popu-
lations were also obtained. In addition, the ecological
aSpectS of the nesting and feeding territories (foraging

areas and feeding activity, number and kinds of arthrOpods

21

22

present, weather conditions, etc.) at eight nests of the
Eastern Phoebe were intensively studied during 1961 and
1962. Due to equipment failure, etc., complete data for
the first 12 days of nestling life, however, were obtained
during only six nesting periods at three nesting Sites
(Nos. l6, l7, and 22).

Growth of Nestlings

 

Weight.——Both first— and second-brood young phoebes
in this study weighed approximately two grams at hatching.
This weight increased to approximately 20 grams by two
weeks of age. Tables 1 and 2 Show that there is a very
rapid gain in weight during the first nine days of life and
a gradually decreasing rate thereafter, until the young are
nearly ready to fledge. The average weight of a nine day
old nestling in this study was 16 grams. This is 88 percent
of the weight of an average 14 day Old phoebe in the study.

As Tables 1 and 2 indicate, the second—brood young
increased in weight, on the average, as rapidly as first—
brood young during the first two days of nestling life. At
three days of age, however, the first-brood young began to
increase their weight at a much faster pace. This average
weight-gain difference between first- and second—brood
young increased until the birds were nearly 12 days of age,
at which time the mean weight for the second—brood young

appeared to be increasing rapidly again. From 13 days

23

until fledging, the young included in this study in both
first— and second—broods averaged approximately the same
weight.

The mean banding—record weight of 24 adult Eastern
Phoebes captured in this study was 24.1 grams. The data
in Tables 1 and 2, therefore, indicate that the young
phoebe gains over one-half of its total adult body weight
during the first week of life.

Length.-—The difference in growth in length between
the first- and second—brood of young phoebes followed a
pattern similar to the differences in daily weight gain in
this study. Unlike the weight gain pattern, however, Tables
1 and 2 Show that for both first- and second-brood young the
daily gain in length proceeds at a fairly uniform pace dur-
ing their entire nestling lives.

At hatching the average young phoebe was approximately
38 millimeters in length. This increased to approximately
125 millimeters at two weeks of age. After three days of
age, however, the young in the second broods showed a some-
what slower length gain each day than those young in the
first-broods.

Feather growth.—-The measurements of the body feathers

 

indicate that they grow at rapid and uniform rates during
the entire nestling period. As with weight and length
growth-rates, however, the growth of feathers in the second-

brood young did not proceed as rapidly as in the first broods.

H

 

24

In general, the entire body of the young phoebe had
down feathers along most tracts at hatching. These were
either sparsely distributed or extremely thick, with a
somewhat matted appearance. Along the caudal tract it was
usually only certain pairs of feathers that had down (most
often only the outer two pairs of feathers and/or the inner—
most pair). In most individuals measured in this study
only the sixth, seventh, eighth, and ninth primary feathers
had down. When the wing was folded the primary down lay
next to the dorsal tract down, and the much more plentiful
secondary down (occurring at each point where a secondary
feather arises) covered all of the cervical apterium. The
down on the head (capital tract) was very long (five to
eight millimeters) and dense at hatching. When the head
was held against the trunk of the body, the head down effec—
tively covered the downless area between the posterior end
of the capital tract and the anterior end of the dorsal
tract. The dorsal tract appeared to have a very dense
covering of down at every point where a definitive feather
was to arise. Actually, only the middle pair of dorsal
tract feather rows had down. The outer two feather rows
were completely bare. The down over the eye, on the back
of the head, and along the upper arm was seven millimeters
at hatching; the crural tract down was five millimeters.
Most down feathers were five-branched and the major portion

of the upper surface of the young phoebe (that portion

25

exposed while in the nest) was almost completely covered at
hatching with down between five and nine millimeters in
length.

The ventral portion of the body was more Sparsely
covered. At hatching the down was concentrated along the
posterior one-fourth of the ventral tract (the portion ex—
posed to the environment while the young is in the nest).
In this region it was Six millimeters at hatching and it
remained approximately the same length until the young was
nearly nine days of age, at which time most of it had been
rubbed Off by the bird's movements. The anterior three-
fourths of the ventral tract never had down on the young in
this study.

The barbed portions of the juvenal feathers along all
major trunk tracts unfurled from their sheaths at approxi-
mately Six days of age. The growth of down and juvenal
feathers along the wings progressed at a rate Similar to
that of the juvenal feathers and down along the major trunk
tracts. The barbed portion of the primaries and secondaries
and of their greater covert feathers also began unfurling
at six days of age, when the steel gray shafts of feathers
along these tracts turned white on their tips and began to
disintegrate as the barbed portions unfurled. The barbs
along all feather tracts continued unfurling at a very rapid

and uniform rate until the young left the nest.

26

Pledging of Nestlings

 

No measurements or experiments were made after the
young were 14 days of age for fear of interfering with
normal fledging time, and in no case were more than one-
half of the young from one nest used in any experiments.

0f the 32 nests studied between 1958 and 1961, 83
young (63.4 per cent) successfully fledged (out of a total
of 131 eggs laid). Of these nests, 11 were re-used for
second—broods. In the 21 first—brood nests (in which 94
eggs were laid), 60 young (63.4 per cent) successfully
fledged. In the re—used, second-brood nests (in which 37
eggs were laid), 23 young (62.1 per cent) fledged success-
fully.

The average fledging time for the 60 first-nest young
was 14.8 days (the earliest 14.1 days, the latest 15.5
days). For the 23 second-brood young, the average fledging
time was 16.9 days (the earliest 15.8 days, the latest 17.4
days). Thus, in this study, the average fledging difference

in time between first— and second-brood young was 2.1 days.

Growth of EctOparaSite POpulations on Young
At hatching, no ectOparasites were found on any first-
brood young. By the second day of nestling life, however,
the 10 young that were sampled (five in 1959; five in 1960)
had an average of 11 ectoparasites (the minimum number was
3; the maximum, 16). The parasites belonged to three groups:

the bird lice (Mallophaga), the mites (Acarina) and one

27

Species of Diptera larvae (only two on one individual). No
attempt was made to collect permanently any parasites until
the birds were 14 days old, but as accurate 3 count as possi—
ble was made on five randomly chosen first- and second-brood
young on each day of nestling life during the 1959 and 1960
nesting seasons. Inasmuch as the number of Mallophaga
remained fairly constant (the greatest number on one individ-
ual was 5) after five days of age, only the counts of mites
are presented in this study. Graph I shows the relationship
between the mean number of mites from the individuals in the
sample and their ages in both first- and second—broods. The
greatest number of ectOparasites on any one young was 242
mites and 4 lice on a 14 day old nestling from a second-brood.
AS Graph I shows, there was a tremendous increase in the mite

populations on the second-brood young in this study.

Cowbird Parasitism
Three nests (9.4 per cent) contained Six cowbird eggs
which time author removed as soon as they were discovered.

All parasitized nests were under bridges.

Development of Temperature Regulation in Young
Internal body temperatures.-—The thermoregulatory
ability of the 15 first-brood and 10 second—brood young used
in the temperature regulation experiments showed considerable
correlation with body growth and development of feathers (see

Tables 3 and 4). At 10 degrees centigrade the one day old

28

nestling was capable of maintaining a body temperature only
a few degrees above that of the experimental environment.

At this environmental temperature the average one day old
young exhibited no breathing movements or pulse for approxi-
mately eight minutes after the conclusion of the experiments.
Gradually the thermoregulatory ability improved, and at 10
days of age the young were able to maintain an internal tem—
perature closely approximating that of the adult bird.

(The mean body temperature of five adult phoebes subjected
to identical environmental conditions was 35.4°C. in 10°C.
environments and 37.8°C. in 40°C. environments.) Nestlings
between 11 and 14 days of age improved only slightly their
ability to maintain high body temperatures in the cool
(10°C.) environment. At a 40°C. environmental temperature,
the one to ten day old first—brood nestlings maintained body
temperatures only a few degrees less than the experimental
temperatures. After 15) days they maintained a constant
body temperature approximating that exhibited by the adults
regardless of the ambient temperature in which they

were placed.

In these experiments the pattern of develOpment of the
thermoregulatory ability of the second-brood young was, at
first, similar to that of the first-brood young at both high
and low experimental temperatures. The older, second-brood
young, however, differed considerably from the first-brood

young in their ability to maintain constant internal

29

temperatures. This was most noticeable at the lower
(10°C.) environmental temperature. The 14 day old, second-
brood young maintained a body temperature comparable to the
average for the nine day Old, first-brood nestlings. This
is somewhat surprising in view of the similarity in Size
and development of these 14 day old young (Tables 1 and 2).
At higher temperatures, too, the second-brood 10 to 14 day
Old young, on the average, develOped much higher tempera-
tures than any of the first-brood young.

Breathing movements.—-Investigations of the breathing

 

movements showed, in general, that both first- and second-
brood young develOped more uniform breathing movements in
both high and low temperature environments as they grew
older (see Tables 3 and 4). AS Graph II shows, the mean
difference in number of breaths/minute between the low
(10°C.) and high (40°C.) environmental exposures for first-
and second-brood young averaged over 100 breaths/minute
until seven days of age. Between 7 and 10 days of age, how-
ever, this difference rapidly diminished by one—half, and
after 10 days of age by approximately three-fourths. As
Graph II also shows there is a considerable difference
between the breathing movements of first- and second-brood
nestlings in the controlled temperature environments after
three days of age. This difference was greatest between 10
and 14 days of age when the mean difference in breathing

movements between high and low temperature exposures for

3O

first—brood young is approximately one-half that of second—
brood young.

ReSponses of ypung after two—hour exposures to con-

 

trolled temperature environmentS.-—After being subjected to

 

two hours of a continuous 10°C. environment, the one to four
day old young were mostly immobile. They did not attempt
to right themselves when placed on their backs, their mand—
ibles were closed and they exhibited only slight breathing
movements. Their skin had a wrinkled, ashy appearance (from
the constriction of the blood capillaries in the Skin).
Within a Short period (up to 13 minutes in one day old
young; up to two minutes in four day old young) breathing
became normal, the skin again appeared pink and all other
movements returned to normal. 0n the average the older (8
to 14 day old) second—brood young in the cool and warm
temperature controlled environments and the younger (one to
Six day Old) second-brood young in the warmer environment
appeared to move much more than did the first-brood young
under similar conditions.

ReSponses of young after one-half hour exposures to

controlled temperature environmentS.-—The 12 first- and 17

 

second—brood, randomly selected, one to six day old young
exposed to shorter, one—half hour controlled temperature
environments during 1960 and 1961 showed no Significant dif-
ference (at the 5 per cent level) in their gaping reSponses

at each day of age under similar temperature exposures. AS

31

is evident in Table 5, however, there was a significant dif-
ference in the mean number of gapes between each group ex-
posed to 10°C., 25°C., and 40°C. during the 30 trials of
trying to illicit the gaping reSponse. As was expected, the
young subjected to the one-half hour exposures were much
more active than those subjected to longer exposure.

Even during a one-half hour exposure to 10°C. and 40°C.
temperature environments, the young in both brood groups
showed a significant inability to gape every time when mech-
anically stimulated when compared to the young exposed to

the 25°C. temperature environment.

Study of Nestlings' Environment

During six 12 day periods, complete environmental in-
formation for three nesting areas containing five two—young
nests and one four-young nest was obtained during 1961 and
1962. For convenience of treatment, the results in this
part of the investigation are separated into (1) the general
nesting activities of the adults, including the size and
nature of the foraging areas (i.e., weather conditions,
numbers and kinds of arthrOpodS present, etc.) and the
adult's relationships with the young (including feeding and
brooding behavior); and (2) the growth and activities of the
young.

Size and general nature of foraging areas.--The average
size of the three areas where feeding activities of the

adults were intensively studied in 1961-1962 was 4727 square

32

meters (3807, 5132, and 5234 square meters). The most
striking feature of each foraging area each year was its
similarity in Size during the four nesting seasons when
maps of these same nesting areas were constructed. The
total area changes made at any one foraging location during
the four year period (determined by calculating the dif-
ference between the largest and smallest areas and again
setting up a weight-area prOportion Similar to the tech—
nique used for determining total foraging areas) was 18 per
cent. The average of all changes at all three locations
during the four year period was only 7 per cent.

In general, the foraging areas at all three nesting
locations were very similar in vegetative make-up and land
use. Two areas bordered streams and all were in Openings
in mature woods. All these nests were built under over-
hanging roofs of private homes on ledges approximately seven
feet above the ground. This same above—ground height of
each nest was approximately maintained after each had been
transferred to the nesting platform cage.

The most significant changes noticed in the individual
foraging areas occurred during periods of very adverse
weather conditions, eSpecially during periods of heavy rain-
fall and/or strong winds (15 miles per hour or greater).
This amounted to a very dramatic change in the portion of
the area utilized by the adults at nesting site number 17
(Nests No. 61-17, 62-17, and 62-173). On August 4 and 8,

33

1962, the adults at this site fed only along the very
sheltered stream bank, 15 meters from their nest during
both five hour periods of moderately heavy rain (approxi-
mately one inch during each five hour period). This was
nearly an 80 per cent reduction in the total foraging area
that they had utilized during the previous week. High
winds (gusts up to 40 miles per hour for periods of 10
minutes or more) on May 27, 1961, in the foraging area at
Nest No. 61-16 resulted in both adults utilizing only the
immediate area below the nest, feeding mostly on or near
the ground along the leeward side of the house where the
nest was placed. This ground-feeding behavior was also
recorded at Nests No. 62—17 on May 24, 1962, during several
one-half hour periods of high (30-40 mph) winds, and at
Nest No. 62-17B on August 4, 1962, during high (20-30 mph)
windy periods of 15 minutes or more between moderately
heavy periods of rain.

Weather conditions in foraging areaS.--Although the
overall weather conditions in Isabella County during the
phoebe'S nesting periods in 1961 and 1962 were very Similar
and deviated little from the previous ten year averages for
the area (U. 8. Dept. of Commerce, 1961, 1962), the weather
conditions appeared to be the most fluctuating ecological
factors in this study.

Table 12 summarizes the mean air temperatures, relative

humidity, wind Speeds, light conditions, and precipitation

34

during the feeding periods of the adults in all foraging
areas studied between May 24—June 4, June 20—July 1, July 8-
July 19, 1961, and between May l8-May 29, July 3—July 14,
and July 28-August 8, 1962. This table was constructed

from daily data summaries shown for each nest in Tables 6
through 11.

Although air temperature, relative humidity, and
inches of rainfall were continuously recorded, the criterion
used for determining the period during which the weather
conditions would be tabulated was the total feeding period
of the nightly brooding adult. Thus, the weather conditions
presented in this table represent only those conditions
which existed from the time of the first feeding trip in
the morning until the last feeding trip at night. These
daily time periods are shown in Tables 6 through 11 under
the column labeled "Total Feeding Day (Hrs.)" and the mean
values for the 12 day period at each nest are summarized
under the same heading in Table 12.

The daily average weather conditions for all foraging
areas during periods of adult feeding for the two year
study period (72 days) were: air temperature, 21.5°C (mean
range 14.8°C.-— 28.5°C.); relative humidity, 69% (mean
range 34.2% ——94.0%); wind Speed, 3.2 miles per hour (mean
range = 1 mph -—20 mph).

During the same time period, there was a total of 3.93
inches of rainfall (28 hours) in 1961 and 2.84 inches (33

34

during the feeding periods of the adults in all foraging
areas studied between May 24-June 4, June 20-July 1, July 8—
July 19, 1961, and between May 18-May 29, July 3—July 14,
and July 28—August 8, 1962. This table was constructed

from daily data summaries shown for each nest in Tables 6
through 11.

Although air temperature, relative humidity, and
inches of rainfall were continuously recorded, the criterion
used for determining the period during which the weather
conditions would be tabulated was the total feeding period
of the nightly brooding adult. Thus, the weather conditions
presented in this table represent only those conditions
which existed from the time of the first feeding trip in
the morning until the last feeding trip at night. These
daily time periods are shown in Tables 6 through 11 under
the column labeled "Total Feeding Day (Hrs.)" and the mean
values for the 12 day period at each nest are summarized
under the same heading in Table 12.

The daily average weather conditions for all foraging
areas during periods of adult feeding for the two year
study period (72 days) were: air temperature, 21.5°C (mean
range l4.8°C.-— 28.5°C.); relative humidity, 69% (mean
range 34.2% —-94.0%); wind speed, 3.2 miles per hour (mean
range = l mph-—20 mph).

During the same time period, there was a total of 3.93

inches of rainfall (28 hours) in 1961 and 2.84 inches (33

hours) in 1962. The period of rain hours (mean daily values
of 2.37 hours in 1961 and 2.73 hours in 1962) was recorded
in each foraging area and is tabulated daily in Tables 6
through 11 and summarized in Table 12.

Light conditions were quite variable during the total
periods of adult foraging. So as to have light values that
could be compared to other weather factors, a light intensity
coding system (described on p.19) for per cent of sky cover
was employed. The numbers of hours of sunny, cloudy, and over
overcast light conditions were then reduced to a fractional
value of sunny hours (S) overcase hours (0) for each daily
foraging time period. These fractional values are given in
Tables 6 through 11. (Hours of ”cloudy” sky cover can be
determined easily by subtracting the total hours of "sunny”
§3g_"overcast" hours from the number of hours, rounded off
to the nearest whole number, in the column headed "Total
Feeding Day.") The total 12 day period is summarized at the
bottom of each of these columns, and a light intensity aver-
age (the quotent of S/O) is shown as the mean light intensity
quotient for that nesting period. Naturally, the value of
S/O increases as the number of "sunny” hours increases. The
mean light quotients for all nests are summarized in Table
12. As this table shows, the average light quotient for the
six nest study period was 0.85, indicating nearly equal
periods of overcast and sunny sky conditions for the entire

study period.

36

Kinds and densities of arthropods in foraging areas.-—

 

Representatives of 16 arthropod orders were collected on the
wind-vane sampling boards during the entire study period.

As Table 13 indicates, l4 insect orders and two arachnoid
orders (Spiders and mites) were collected in the samples.
Table 13 shows the total number of individuals of each order
collected and the number of days in the 12 day period when
the order was recorded at each nesting location. The nests
in this table are arranged in order by earliest month and
day (rather than by year). The most striking feature of
this table is the seasonal change in numbers of individuals
collected. Seasonally, the numbers of ColeOptera and
EphemerOptera seemed to be quite plentiful during the early
nesting periods and then gradually diminished as the season
progressed. By contrast, the numbers of HymenOptera, Homo-
ptera, Hemiptera, and Araneae seemed to increase gradually
as the season progressed. Diptera numbers increased until
the middle of the whole nesting season and then appeared to
decrease gradually. Several orders (Acarina, LepidOptera,
and NeurOptera) seemed to fluctuate very little in the
samples as the season progressed. However, Plec0ptera were
captured only during late May and early June, and Odonata
were sampled only during early July. The other orders were
represented by only a few individuals on such a small number
of days that any pattern in their changing abundance was not

revealed. An interesting massive occurrence of thrips

37

(ThysanOptera), however, was recorded at Nest No. 62—17B on
July 29, 1962. Approximately 15 minutes before removing

the sampling boards for the evening, hundreds of thrips were
captured. They were definitely not on the boards in any
numbers prior to this time because the tree tanglefood had
been changed the previous evening and the Speckled appear-
ance caused by the thrip's presence was not evident until a
short time before the boards were removed. That evening, a
careful examination revealed that 1197 individuals, weigh-
ing 0.0352 grams, had been sampled in that short period
(compared to 73 other arthrOpods on the same boards weigh-
ing 0.1523 grams for the total feeding day period). Because
these were collected at the approximate time that foraging
by the adults had ceased for the day, they were not included
in that day's calculations.

As Table 13 shows, slightly more than 98 per cent of
all arthrOpodS sampled on the collecting boards during the
entire nesting study belonged to seven orders. Three orders
alone comprised 89 per cent of the total sample in all
foraging areas studied (Diptera, 60.2 per cent; ColeOptera,
18.8 per cent; HymenOptera, 10 per cent). Surprisingly,
Spiders appeared commonly on the sampling boards during the
latter partcfi'June through early August. All Specimens were
quite small.

The total daily weight and number of arthrOpods are

aleso shown in Tables 6 through 11, and the means of all Six,

 

38

l2—day nesting periods studied are summarized in Table 12.
The data in Table 12 indicate that there were Significant
seasonal changes in the total numbers and weights of arthro—
pods sampled in the foraging areas during the total period
when nestlings were being fed. These data and the data in
Table 13 suggest that even though there were noticeable
changes in the kinds of arthropods present in these foraging
areas, there appearedto'be much replacement by other groups.
On a daily basis, there seemed to be dramatic changes
in the numbers and total weight of arthrOpods sampled under
different weather conditions in the foraging areas. Further-
more, general observations seemed to suggest that certain
groups were not as abundant (or were more abundant) in cer-
tain foraging areas during very dramatic weather changes.
To help determine whether weather conditions had affected
the samples of numbers and weights of the arthropods in the
foraging areas, the arthropod data (in this case number of
arthropods) and correSponding weather data (rain hours, wind
speed, air temperature, relative humidity and light inten-
sity) were graphically plotted to see if there appeared to
be any relationship between these data. Graph III shows
the mean number of arthropods plotted against the various
mean weather conditions already mentioned. Correlation co-
efficients (r) of these sets of data were then calculated.
leese r values showed y§§y_high positive correlations in the

caseaiof mean daily air temperature (r = +0.82) and mean light

39

intensity (r = +0.91), and an extremely high negative cor-

 

relation in regards to mean daily wind Speeds (r = -0.98).
When plotted against mean daily rain hours, however, the
number of arthropods showed only a suggestive (but perhaps
Significant) negative correlation (r=-0.55).

Collectively, the above statistics suggest that in
this study the number of arthrOpods (and also the weight
of arthropods-—inasmuch as the two are so strongly corre—
lated) and the weather conditions were very strongly related
within the adult phoebe's foraging areas.

Feeding behavior.——Although it was never possible to

 

distinguish between the sexes of the adults at any of the
six nests in this study, this writer was able to color mark
and band an adult male at one nest during 1960 when the
equipment for the 1961-62 study was being perfected. This
occurred when the young in the nest were 13 days old. At
8:15 a.m. the male mounted the female in a nearby tree and
flew immediately towards the nest where he was captured in
a mist net.

Even though the adults were not sexed at the six nests
in this part of the study, over 350 hours of observations at
all nests showed that both adults always fed the young.
During a total of 48 hours, moreover, it was possible to
determine the extent of feeding by individual, color-marked
(but not sexed) adults at two nests. The data collected

during this period (when the young were one to seven days

40

of age) did not reveal any significant difference in the
number of feeding trips made by either adult, except during
the first hour of daily feeding. During this latter period,
the non-brooding adults at both nests fed 78 per cent times
more than the brooding adults; the brooders, on the other
hand, seemed to do most of the feeding just prior to nightly
brooding.

There appeared to be a regular ritual associated with
commencing the feeding day by the adults. Usually this
began when the adult non—brooder began calling some distance
from the nest. When this occurred, the brooding bird raised
in the nest. If calling continued, the broder would
occasionally leave the nest. Analysis of the data in this
area, however, revealed no definite pattern. Instead, it
seemed to be a somewhat individual variation among the dif-
ferent nesting pairs. During the May and early June nesting
periods (at Nests 61—16 and 62-17) the non—brooding bird
often brought food to the nest during the first eight days
when young were in the nest, fed its mate, which in turn
passed the food to the young and then left the nest. The
non-brooder usually waited for the feces and after obtaining
them would fly from the nest, returning almost immediately
with food.

At all nesting locations there seemed to be a decided
preference for using particular feeding perches during periods

of fair weather (no rain, low wind). This was exhibited by

41

both adults and, at the two nests where the adults were
individually recognizable, each adult appeared to have indi-
vidual preferences. At Nest No. 62-22A a favored perching
site from which feeding trips were made was a discarded
child's Slide. This slide was approximately 40’ from the
nest from the time the young phoebes hatched until they
were five days of age. The adult non—brooding phoebe used
the tOp two bars of this Slide aS an ”approach” perch
before flying to the nest every morning. Its mate flew to
this same site every morning upon leaving the nest. The
non-brooding bird, after calling a few times, always flew
from this perch to the ground at the base of an elm tree
just in front of the nest, then up to the retaining wall of
the dirt around the tree, and then to the next. When this
writer left his observation tent at 8:15 p.m.,on the night
when the young were five days of age, he moved the child's
Slide 25' further away from the nest, to a point 15' from
where the non-brooding adult usually first appeared in the
morning on the edge of the woods. When the non—brooding
adult appeared at its usual Spot on the edge of the woods
the following morning, it gave a few calls and then flew to
the Spot where the slide had been. Here it hovered for a
second or two, apparently Spotted the slide, and flew to it.
It remained there for only an instant (previously it stayed
long enough to call two or three times and occasionally to

catch an insect) and then flew directly to the nest, where

42

it hovered a few seconds before the brooding adult left.

It landed on the recorder perch but definitely did not feed
the young. Rather, it left almost immediately to join its
mate at the Slide where it_had perched. The following two
mornings theslide was used as an approach and exit perch,
but on the third morning, a small tree closer to the nest
was used. Although the writer returned the Slide that even-
ing to its former position, it was never used as an early
morning approach perch again, although it was occasionally
used during the day as a feeding perch.

Although the average feeding time varied somewhat
seasonally (due to slightly differing daily sunrise and
sunset times) the average length of feeding days at all
nests, from late May to early August, varied little. The
average feeding day at all nests was 14.4 hours with a
range of 12.8--l5.3 hours. The range of the means, however,
for all feeding days at all nests varied by only 0.7 hours,
and there appeared to be no significant relationship between
the mean hours of feeding days and the weather conditions.
The only exception to this was when heavy early morning or
early evening rain or very cold early morning or early
evening temperatures lengthened the nightly brooding period
or shortened the late evening feeding period. There were
only two days (on May 28 and 30 at Nest No. 61—16) when the
above situations occurred and the loss in feeding time from

the previous day in each case averaged nearly one hour.

43

The most numerous trips (+ 51 per cent) to the nests,
presumably each time with food, were made at all nests during
the early morning (5:05 a.m. to 7:15 a.m.) and early evening
(6:25 p.m. to 7:25 p.m.). Again, however, this time was
delayed somewhat by adverse weather. At Nest NO. 61-16,
during cold, rainy morning weather, the greatest number of
early morning feeding trips occurred between 7:30 a.m. and
9:55 a.m. on May 28 and between 7:10 a.m. and 9:30 a.m. on
May 30.

Approximately 12 times each day (during a daily mini—
mum of five hours that was Spent at each nest), this writer
witnessed and recorded food caught by the adults. Careful
observations of 783 such catches Showed that all feeding was
done in a hovering position or made as a sw00ping catch as
an insect jumped (particularly in the case of grasshOpperS
watched being captured). 0f the 783 catches witnessed, 406
(52 per cent) were made in Open air, 252 (32 per cent) were
made in foliage (partly in Open air, partly off leaves), and
125 (16 per cent) were made directly above the ground. The
estimated maximum height of all catches was 12—1/2 feet. In
all observations the Observer never witnessed more than one
catch per feeding trip to the nest (but this was determined
for only 86 trips or 11 per cent of all observations).

Although Henderson (1924) found that the Size of the
insects taken increased as the young increased in age; this
was not true of this writer's observations. It seemed rather

thenztfim adults captured and fed whatever was available.

44

The total trips made to the nest by the adults is
shown for each day at each nest in Tables 6 through 11 and
the mean daily trips are summarized in Table 12. The rela-
tionships between mean weather conditions and the mean num—
ber of nest trips (taken from Table 12) are plotted against
one another in Graph IV (D., E., F., G.). Correlations co-
efficients of these values showed relatively strong correla-
tions between number of trips and air temperatures
(r = —0.65). Extremely high correlations were calculated
for number of trips and daily wind speed (r = -0.98), and
number of trips and light intensity (r = +0.83). These
statistics indicate that those weather factors analyzed and
the number of trips made to the nests by the adults in this
study are very strongly related. The same appears to be
true for the mean number of trips to the nest by the adults
and number of arthrOpods present in the foraging areas
(r = +0.95 for mean numbers of arthrOpods present and r =
+0.94 for mean weight of arthrOpods present). In addition,
there appears to be a strong negative relationship (r =
—0.73) between the mean daily number of trips during the
first six days at all nests and the mean daily number of
brooding periods by the adults for the same days.

The four-young nest (Table 11) showed that although
the weather conditions were approximately the same as the
mean weather values at the two-young nests for the 12 day
study period (Table 12), the mean daily number of trips to

thee nest were nearly 70 per cent greater.

45

Brooding behavior.—-Brooding periods were impossible

 

to determine from the thermistor probe records after six
days of age due to the increased body temperatures of the
young. Nest temperatures, however, were continuously
recorded during the entire nesting period.

Temperatures obtained continuously at the bottom of
the nests generally followed the temperature of the brooding
adult. During daily non-brooding periods of 8 to 10 minutes,
however, nest temperatures in the two~young nests in this
study often drOpped as much as 6°C. (in nests containing
7 day old young) to 18°C. (in nests containing 2 day old
young). The nest temperatures at night were fairly uniform
during the first ten days of the nestlings' life. Except
on very cold nights brooding usually ceased after this
period. Of 24 nightly observations (between 11:00 p.m. and
3:00 a.m. at three nests) there was only one instance when
it at least appeared that older young (16 days Old) were
being brooded. This was at Nest NO. 62-17 on June 2 (3:30
a.m.) when the air temperature was 7°C.

Usually, one adult was seen on the young or on the rim
of the nest (even with young 14 days of age) during the
nightime. In the case of the two nests, where at least one
adult was color marked, it was always the same adult that
brooded the young at night,but during the day, on six dif—
ferent occasions,the writer Observed the other adults

brooding for short periods.

46

In the case of young between the ages of three days
to fledging there were often uniform interruptions in the
brooding behavior. Twenty-four nightly temperature records
of nests with young between three and nine days of age
showed uniform temperature changes of five to eight degrees
centrigrade approximately every 20—35 minutes. Several ob-
servations with a flashlight indicated that the adult bird
was standing up in the nest. Perhaps this behavior was in
reSponse to movements by the young, or perhaps it was
merely due to increasing irritability to the adult's brood
patch. This response did not take place when the nestlings
were younger (nor very noticeably during the day).

In heavily parasitized second—brood nests there were
almost continuous temperature changes during both daily and
nightly periods. Analysis of eight days and nights at both
first-brood and second-brood nests containing young between
three and six days of age Showed that the second—brood
nests had an average 4°C. higher temperature than nests
containing first—brood young

When the mean number of brooding periods for all two-
young nests were plotted against the mean feeding trips for
the first six days, a negative correlation (r = -0.73) was
obtained. In the Single four-young nest (Table 11) there
was a daily average of 2.4 less daily brooding periods and
one less hour Spent during the first six days in brooding

the young. In general, the nest temperatures at the bottom

47

of this nest were always several degrees above the average
nest-bottom temperatures in the five two—young nests.

Nest desertion.-—During the total five year period

 

when the Eastern Phoebe was being studied (1958-1962) there
were three cases of nest desertion. Two of these occurred
in 1960 while the equipment and techniques were being per-
fected for use during the intensive environmental studies.
Both cases involved moving the nest to a nesting platform
cage before the eggs had hatched (in the first case, three
days before the estimated hatching date; in the second case,
one day before the estimated date). Switching ten other
nests to this platform when the young were only a few hours
old, however, did not cause desertion .

The third case of nest desertion occurred in 1962
when the artificial nesting (Plate 8) was being used in a
second attempt to collect food fed to the young. Although
an attempt in 1961 illicited no response from the adults
(and was used for only one hour at a nest containing two
eight day old young), the 1962 experiment with this nestling
involved a full feeding day in a nest containing two three—
day old nestlings. Much directing behavior by the adults
was made with this nestling (placing their mandibles into
the Opened mandibles of the nestling but not feeding it),
but many attempts to brood the two live nestlings seemed
to be prevented by the presence of the artifical nestling's

slightly raised (and closed) mandibles. After three hours

48

of not being brooded, in an air temperature of 18°C., the
live nestlings finally slowed their gaping reSponse to only
about once every fourth trip made to the nest by the adults.
After four hours (at 7:00 p.m.) they appeared to be making
only occasional attempts to gape. The adults at this point
apparently deserted, even though the live young were returned
to their original nest. These Observations possibly indicate
that desertion was due to a lack of reSponse on the part of
the young. The young were inactive, cold, but alive, the
following morning and they were removed to another nest

where three, five day old phoebes were being raised. All
five young fledged together 12 days later.

DevelOpment and Activities of
the Nestlings

 

 

Growth.--Except for being slightly heavier at one day
of age, the weight-growth pattern of the nestlings in the
two-young nests followed essentially the same growth pattern
exhibited by the young in the earlier (1958—1959) growth
studies of 25 first-brood and 13 second—brood young (see
Tables 1, 2, and 6 through 11). On the average, however,
the young in the two-young broods were heavier during the
last few days of the measurement period (11 and 12 days of
age). The most notable difference was in the case of heavier
second-brood young (Nests No. 61-16A, 62-17B, 62-22A) as
compared to the Second-brood young in the general growth

studies of 1958-1959 (Table 2). The latter young were an

49

average of one to two grams lighter for each day of age
than the young in the two-brood nests in this part of the
investigation. Possibly this was due to the presence Of
greater mite pOpulationS and to a greater number of young
per nest. The first—brood in the four—young nest (No.
61-17) also weighed more daily than the second—brood young
in the 1958-1959 general growth studies.

The daily weight gains of the nestlings in the two-
young nests are Shown in Tables 6 through 10 and summarized
in Table 12. The mean weight gains for these young are
also plotted against environmental factors on Graph V.
There appears to be little correlation between the daily
weight gains of these young and their fledging age (Graph
V,A). Also, there appears to be only slight correlation
between number of rain hours (r = +0.5), wind speed (r =
+0.45), or air temperature (r = -0.45). When plotted
against mean number of adult trips to the nest (presumably
with food) there appears to be only a slight (although neg-
ative) correlation (r = —0.46). This correlation seems to
coincide with the correlation coefficient for daily weight
gain and the daily mean numbers of arthropods available in
the foraging areas of the adults (r = -0.57).

The above statistical analysis seems to suggest that
the daily weight gain of the young is almost independent
of environmental factors (length of time in the nest, amount

of food available to the adults, number of trips to the nest

50

by the adults, or the weather conditions, which have already
been shown to be strongly correlated with these other
factors.)

DevelOpment of behavior in the nest.-—At hatching the

 

young phoebes were relatively helpless. The muscles in the
neck appeared to be the most highly coordinated, and the
young were capable of raising and moving the head in several
uncoordinated directions. The gaping relfex was evident
within one hour after hatching. Touching the edge of the
nest, the bill, or the Side of the head produced this
reSponse. The reSponse consisted of a rapid upward extension
of the neck and head, opening of the mandibles and lowering
of the head. Simultaneous to the gaping response was an
extension posteriorly of the legs and a slight Opening and
closing of the toes. Although there was some movement of
the wings at this time there appeared to be no movement that
would extend them. Seven one-hour old nestlings (when the
down had just completely dried) were placed on their backs
but they immediately turned on their sides (the normal posi—
tion at this time), apparently using only their neck muscles
to attain this position. The eyes were closed at hatching.
Although, as already mentioned, there were some leg
movements shortly after hatching, the young could not ef-
fectively raise their bodies with their legs until approxi—
mately two and one—half days of age. The grasping reflex

in the toes was not very effective until three days of age,

51

at which time the young firmly clutched the lining materials
of the nest.

The eyes of the young phoebes opened at five and one—
half to six and one—half days of age. At this time there
was a noticeable increase in body movements; the wings were
very often extended and folded as the head raised with a
gaping reflex. The gape at first was accompanied by a
vertical extension of the neck. With each gape at this
time, however, the eyelids opened, and, by the day following
the Opening of the eyes, the gape began to be directed
towards the parent bird (or to a human hand).

Since all young were color-marked on the first day it
was possible to keep track of their relative positions in
the nest. In two nests in 1961 the young were always re-
turned to the approximate position in which they were
originally found. In every case there were no changes in
these positions throughout the first seven days of nestling
life. Apparently the clutching reflex during the first
seven days establishes not only an anchor to the nest lining
but also determines the position of each nestling in the
nest. The nestlings, from the beginning of time that they
clutched the nest lining, huddled together. The cup—shaped
nest, determined originally by the ventral contour of the
adult, partly assured this huddling effect.

From the first day after hatching until the nestlings

fledged, the gaping reSponse was more often accompanied by

52

a short call or "begging" notes. Until the eyes Opened
these notes could be elicited by any gape releasing stimu-
lus. After the eyes Opened this calling became increasingly
louder and longer in duration, and, near the end of the
nestling period, usually preceded the landing of the adult
on the nest rim. Numerous observations indicated that, at
least after the young were seven to nine days of age, one
young calling caused the other young to gape and to call.
Until the young were approximately eight days old
they always gaped when the edge of the nest was jarred
except immediately after being fed by the adults. By the
ninth day this response decreased considerably. All other
movements in the nest seemed to increase considerably at
this time, however. 0n warm days the young often huddled
on the windward side of the nest with their heads resting
on the nest's rim and their mandibles partly Open. In this
position they were seen panting in the nest when the ambient
temperature was above 30°C. Between nine and ten days of
age a crouching reflex (lowering the head and withdrawing
it, compressing the wings against the side of the body,
tightening the toes) was observed. Foreign objects (a stick
or a human hand) presented to the young caused them to
extend the wings and snap the mandibles, producing a noise
similar to that made by the adults when frightened off the
nest. During this same period the young began very active

wing movements. This was usually accompanied by raising

53

and lowering the body in the nest. By the tenth to twelfth
day of age the nestlings would occasionally raise their toes
from the nest lining and grasp either the side of the nest

or the feathers of one of their Siblings. Then the entangled
sibling would also being rapid movements until it was dis—
entangled. This shifting in the nest continued until the
young fledged.

In general, the main behavioral difference between
first- and second—brood young was the greater movement of
the second-broods during the last half (Seven days of age
or older) of their nestling period. This movement appeared
to be mainly directed at rubbing against the sides of the
nest and, at approximately nine days of age until fledging,
at pecking at mites in the nest and on their Siblings.

Fledging.--Although no environmental or growth meas-
urements were made after the end of the twelfth day, several
daily observations were continued SO as to determine the
fledging time of the young. The average age at fledging
time of the first—brood two young nestlings was 16.2 days;
for the second-brood nestlings it was 17 days. This indi-
cates a somewhat longer (1.4 days) nestling period for the
first—brood young than that determined for the 60 first-
brood young from normal nests in the 1958-1961 study period.
It was almost the same for the second—brood young, however,
when compared to the fledging time of 23 second—brood young

from normal nests in the 1958-1961 study period.

DISCUSSION AND CONCLUSIONS

Probably the first worker to study in detail the
growth and develOpment of temperature regulation in nestl-
ing Eastern Phoebes was Stoner (1939). His three year study
involved field investigations of growth and body tempera—
tures of 20 young and the body temperatures of two adults.
His growth measurements for 12 young included body weight,
ulna, humerus, tarsus, hind toe and claw lengths, lengths
of feathered areas(outer and inner primary and covert
feathers, outer and inner tail feathers), widths of bill at
the nostril and at the gape, and width of head behind eyes.
In general, he found three distinct periods of growth:

" an initial, postnatal interval of comparatively

slow growth approximately three days in length; a Space of

vigorous growth covering nine to ten days; and a stage of

 

retarded and m2§§_93_less fluctuatipg growth occupying the
remaining four to five days spent in the nest.” His meas-
urements and conclusions suggested that feather develOpment
followed the most profound increases in body size.

Merry (1941) presented weight, total body length,
average length of primaries, primary coverts, and tail
feathers, wing length, and very general statements on down

feathers at hatching for variable numbers of young between

54

hatching and fledging. Her data, however, were not given
in detail, and it is difficult to Obtain exact measurements
from her graphs Showing averages for these measurements.
In general, however, they seem to agree with the measure-
ments that Stoner found for this Species.

Wetherbee (1957) presented measurements on the down
feathers at hatching for six young phoebes.

This investigation followed as closely as possible
the techniques used by Stoner for determining daily growth
patterns. The measurements which were obtained, however,
were those which this writer felt had most to do with devel-
Opment of temperature regulation in the young. Inasmuch
as the writer was more interested in those feathers which
serve to insulate the young while they are in the nest, he
chose to measure the innermost secondaries, primaries, and
their covert feathers, rather than the outermost primary
feathers which Stoner measured. Total body length measure-
ments were also Obtained in this investigation (not in
Stoner's, however), so as to gain some appreciation for the
rate of increase in mass over surface area which is directly
related to increased temperature control ability. In this
study these measurements showed an increasing mass to body
surface area ratio. This undoubtedly was reflected as
greater heat production and lesser heat dissapation per body
size in the young. Although bony structures, such as those
studied by Stoner, do provide good indications of growth,

they were not measured in this investigation.

56

The growth measurements of nestling phoebes at each
day of age obtained in this study showed great variance
from those recorded by Stoner. As an example, his average
weight measurement for six "one” day old young was 1.9
grams whereas those in this investigation were 3.1 grams
for 25 first-brood young and 2.8 grams for 13 second—brood
young. His average for this particular age, however, was

H

based on six individuals varying in age from three
to twenty-four hours." The mean measurements in this
writer's study were based on individuals no less than 12
nor more than 36 hours in age. Stoner's measurements were

' The measurements in

all made between "10 a.m. to 12m.'
this report were made between 6:30 p.m. and 7:30 p.m. so

as notto interfere with a full day of feeding. The meas-
urements which Merry (1941) collected were so inconsistent
in regards to time when recorded that this investigator

made no attempt to compare her growth data with the growth
data of this report.

In this study, the young phoebes weighed approximately
two grams at hatching. By two weeks of age this weight had
increased to approximately 20 grams. Weight, in general,
increased greatly during the first nine days and gradually
leveled off until the day of fledging. There was a signifi-
cant difference in daily weight gain between first- and
second—brood young after the third day, but this difference

diminished near the end Of the nestling period, so that

57

both brood groups weighed approximately the same at two
weeks of age.

The total body length of young Eastern Phoebes in this
study increased gradually during the entire nestling period.
However, the second-brood young did not Show as great a
daily body length gain as did the first-brood young. At
hatching, the young phoebes were approximately 38 milli-
meters in length. They increased in length to 125 milli-
meters at two weeks of age.

Juvenal feather growth progressed at very rapid rates
after approximately five days of age in the young in this
study. At hatching the young were covered with natal down
along most feather tracts. 0n the alar tracts it was most
dense on the secondaries. 0n the body the down was most
dense in areas that are exposed to the surrounding air
medium when the young are in the nest. The measurements
of these down feathers agree closely with the data presented
by Wetherbee (1957). The juvenal feathers that eventually
cover exposed areas appeared to grow more rapidly than
other body feathers (except for tail feathers), so that by
nine days of age the birds were effectively covered with
juvenal feathers. A difference in feather growth was evi—
dent in first— and second-brood young, following the same
general pattern seen in the weight and length differences
between these two brood groups.

Stoner (1939) showed that the nestling phoebe devel—

oped good temperature control by ten days of age. His

58

method of determining this was by obtaining daily deep body
temperatures in the proventriculus of the young, and com-
paring their body temperatures each day of age with body
temperatures of adults Obtained in a similar fashion. He
concluded that the nestling Eastern Phoebe attains good

body temperature control between nine and ten days of age.
This writer's results, obtained during carefully controlled
experiments in which the young were subjected to tempera-
ture control chambers for two hour periods, indicate the
same thing. The average body temperatures of adults meas—
ured in Stoner's study (109.3°F.) were slightly higher than
the temperatures that this report recorded for adults
(35.4°C. in 10°C. environments, 37.8°C. in 40°C. environ—
ments). This difference is possibly due to the fact that
these were cloacal rather than proventricular temperatures.
As with other measurements in this study, body temperature
control measurements of first— and second—brood young showed
that first—brood young develOped more effective body temper-
ature control in both high (40°C.) and low (10°C.) temper-
ature environments at an earlier age than second-brood
young. As further evidence of this, first—brood young were
better able to control breathing movements (which is directly
related to temperature regulation), at least at older ages,
than were second—brood young. Inasmuch as Stoner did not
separate his young into first- or second—brood groups his
data could not be compared with this study in regards to

any brood gnaup differences.

Several workers (Townsend, 1926; Shelley, 1936; and
Abbott, 1922, 1942) have commented on the presence and
detrimental effects of ectoparasites on the second-broods
of the Eastern Phoebe. This writer's data indicate that
this environmental factor has a great effect on the growth
and develOpment of temperature control in these second-
broods. The data further suggest,however, that the effect
is not great enough to affect eventual fledging of normal
sized second-broods of young, although it may dgggy by a
day or two their fledging time, rather than hasten fledging
by one day as Sherman (as quoted by Bent, 1942) found in
her study of 10 nests.

Although Merry (1941) made general comments on the
behavior of the young, no behavior study of nestling Eastern
Phoebes has been made. The general observations made in
this study indicate a pattern of behavioral development
Similar to other passerine birds. In general, there ap-
peared to be three distinct behavioral periods in the young
in this study: (1) hatching to eyes open, (2) eyes Open to
rapid wing movements, (3) rapid wing movements to fledging.
In most reSpects these three periods coincide with the
three distinct growth periods that Stoner (1939) mentioned
for this species.

In the environmental portion of this investigation
adult attentive behavior data (feeding trips to the nest

and number and duration of brooding periods) were collected.

60

The nature and size of the adult's foraging areas were also
investigated to determine if there were any correlations
between these various factors in the nestling's environment
and the growth of the young.

Several other workers have attempted to show how
several of these factors are related in other Species.

Lack (1956), in summarizing all of his work on the Common

 

Swift, Apus apus, found strong correlations between weather
conditions in the foraging areas and the general growth and
development of the young. He found that ”. . . the weight
curve for the swift is interrupted by Sharp drOps, each of
which corresponds to a Spell of bad weather.” In regards
to feather develOpment and fledging he states that ”.

the growth of feathers on the young swift is greatly re-
tarded when food is Short. As a result the length of time
between the hatching of the swift and its departure from
the nest varies from only five weeks when food is abundant
to as much as eight weeks when it is scarce." Koskimies
(1950), in his thorough review of the literature dealing
with the effects of weather on the same Species, pointed
out that the overall weather (rather than light intensity
alone) was responsible for the awakening time in the adult,
but that light intensity was the most important factor for
cessation of feeding. He also found that the length of
time Spent searching for food depended upon the weather and

the stage of development of the young, and that " . . . the

61

quantitative investigation of the small animals . . . in
the habitat of the species studied gives a basis for com-
parative food—ecological research." He stressed that
weather factors which affect aerial food items must be
understood as a whole rather than as separate parts if
their true effect on biological phenomena is to be cor-
rectly interpreted. His conclusions in regards to the work
of others on the relationship between the feeding habits
and food of the swift, the weight changes of the nestling
swifts, and the effect of the weather on these factors

can be summarized as follows: temperature directly affects
the nature and quantity of insects available to the adults
for feeding the young (after Glick, 1939); the morning
temperature is distinctly correlated to the first morning
flight from the nest (Weitnauer, 1947); low temperatures
delay early morning nest departure; the quantity of aero—
planktonic insects in cold weather is smaller than in warm
weather (thus, the feeding frequency is directly lowered;
Weitnauer, pp, 313,); the feeding frequency is zero at
temperatures of 12°C. or lower; high winds greatly reduce
the numbers of insects (Glick, 1939, and Palmen, 1944);

the convection of the air controls the altitudinal distri-
bution of insects (Wellington, 1945); rain is directly cor-
related with the numbers and kinds of insects present
(Glick, 2p..gig.); cloudiness, in itself, may have no effect

on insect numbers except indirectly, as an indication of the

62

total weather conditions (Palmen, pp, 933,); and swifts do
not feed during poor weather conditions (low temperatures,
heavy rain and high winds). Koskimies also found that in
the swift, at least, poor weather conditions over long
periods of time may cause starvation among the young which
may in time adversely affect their temperature regulation
abilities, and if continued for a long enough period, may
cause death. Sutter (1941) as quoted by Koskimies (9p,
g$£,) found that ”bad weather" delays the develOpment of
temperature regulation and general growth in the Wryneck,

Jynx torquilla.

 

In this study those ecological factors were investi-
gated in the phoebes' foraging areas (aerial arthrOpods and
weather conditions) suggested by Koskimies to have the
greatest relationship to the growth of the Species that he
studied. The arthropods sampled in the fairly uniform-
sized foraging areas in this study were quite Similar to
those sampled over a much longer period of time (and cover-
ing much larger areas to much greater heights) by Click (pp.
232.) in Louisiana. Glick found 44 per cent Diptera, 20
per cent Hemiptera, 17 per cent ColeOptera, 11 per cent
HymenOptera, 6 per cent Araneae, l per cent LepidOptera,
and 1 per cent other groups in his samples of 25,947 indiv-
iduals. At approximately two meters above the ground, this
writer found 60 per cent Diptera, 19 per cent ColeOptera,

10 per cent HymenOptera, 5 per cent HomOptera, 2 per cent

63

Hemiptera, 2 per cent EphemerOptera, and l per cent Araneae,
and 1 per cent other groups during the nestling periods of
the phoebe.

The work of Merry (1941) and others indicates that
the adult phoebes have certain "preferred" food items
(mainly Hymenoptera according to Beal, 1912). This author's
observations, however, indicate that the adults were feeding
on anything that was available.

The correlation between the weather conditions and

insect numbers and their weights was equally significant
when compared to the work of Click (1939) and Palmen (1944)
and the summary made by Koskimies (1950), even though this
investigator's samples were obtained nearer the ground.
High positive correlations were found between numbers of
arthropods, air temperatures, and light intensities; and
high negative correlations were found between numbers of
insects, rain hours, and wind Speeds.

In regards to adult attentive behavior and the weather,
this investigation of the phoebe agrees very closely with
the data that Kendeigh (1952) collected on the effect of air
temperature on trips to the nest by one pair of phoebes.
This author's studies reval an r value of + 0.66 between
trips to the nest and air temperature. Observational data
incidate that the length of the feeding day was shortened
by adverse weather conditions in the early morning or evening.

The data also reveal a high positive correlation between

64

light intensity (+0.83) and nest trips. There were signifi—
cant negative correlations between nest trips, rain hours
and wind Speeds for the first 12 days of nestling life, as
well as between nest trips and brooding periods (-0.73) for
the first Six days of nestling life.

The work by Kendeigh (1952) on the attentive and non—
attentive behavior of adult Eastern Phoebes during one
complete nesting period (June 20—July 8, 1932, at a four-
young nest) and one partial nesting period (June 12-16,

1932, at a nest containing one young, 7-12 days in age)

Showed that the rate of feeding the young was directly

proportional to the number of young in the nest." Although
the present investigation of one four—young nest showed a
far greater number of trips, it was not directly porpor—
tional to the mean number of trips at the five two—young
nests.

These data suggest that insect availability and atten-
tive behavior of the adult phoebes were both strongly cor-
related with the weather factors measured during the five
12 day periods at the two-young nests. The data collected
on mean daily weight gain of these young suggest, however,
that this factor is not very strongly correlated to these
environmental factors. These data suggest, rather, that
the growth of the young is even negatively correlated with
them (i.e., the correlation between insect numbers and rain

hours was -0.55 but between weight gain of the young and

 

65

rain hours, +0.51; between numbers of trips to the nest and
insect numbers it was +0.95 but between numbers of trips to
the nest and weight gain of young, —0.46; and between number
of arthropodS-—presumably available for feeding—-and weight
gain of the young it was -0.57). Perhaps these statistics,
however, in the light of observational data on the behavior
of the adults and young, do show certain very subtle
(although negative) relationship between the rate at which
the young in this study grew and the ecological factors
that were measured. There were several instances in this
study when the adults utilized entirely different foraging
areas during periods of very adverse weather conditions
(see p. 32). Perhaps in so doing the adults come into
contact with larger aerial arthrOpods gg_the average than
they would find on days when g1; aerial arthrOpods were
active. This perhaps would reflect fewer trips to the nest
and possibly even higher weight gain in the young, especially
if the cooler temperatures on such days were at the same
time lowering the energy expenditure of the partially
poikilothermic young. It is also quite possible that a day
with high winds and/or heavy rain would reduce the "avail-
ability" of smaller insects. AS a result each trip made

by the adults would be ”worth more” from the standpoint of
obtaining larger food items for the young. 0n the other
hand, if the gaping reSponse of the young stimulates the

adults to feed, the gaping response experiments performed

66

at cooler temperatures (see p. 30) suggest that the young
would not be gaping as often. Possible this would also de-
crease the number of trips to the nest.
The work with the artificial nesting that resulted

in nest desertion by the adults, possibly by preventing
brooding, and general observations at all nests, however,
suggest that there is a regular sequence of behavioral re-
Sponses between the young phoebe and the adults. That is,
during the daytime feeding periods, as long as the young
gape, they are fed. When they no longer gape, they are
brooded. When they begin to move actively under the adults,
brooding ceases and feeding begins again. This seemed to
be the pattern at every nest where close Observations of
the young and adults at the nest could be made.

Whatever the mechanism involved (and it undoubtedly
is a combination of many factors) there appears, at least,
to be little statistical correlation between the rate at
which the young grew and the weather factors as well as
attentive behavior of the adults in this study. This dis-
agrees to a certain extent with the conclusions of Kendeigh
(1934) that ". . . the growth of the embryo and the nestling
is practically independent of fluctuations or extremes in
envrionmental factors as long as the
adult birds are able to carry on normal activities, the
survival and develOpment of the young progress independently

of environmental conditions." This writer's study on the

 

67

nestling life of the Eastern Phoebe suggests, however, that
the "normal" activities of the adults are directly affected
by the environment and that there are possibly some very
subtle relationships involving the physiological state of
the young (temperature regulatory ability) and behavioral
relationships between the young and the adults that need
further study. It may well be that the altricial nestling
phoebe contributes as much to its own survival as does its
parents by possessing the poikilothermic condition at a
very critical period in its life.

In conclusion, this study indicates that the environ—
ment of the nestling Eastern Phoebe indirectly, at least,
has a great effect on its growth and develOpment, through
the effect of the weather on the food supply and the effect
of the weather on the behavior of the adults. It is also
seen in the detrimental effect of numerous ectOparasites on
second-brood young. The environment appears to have a
direct effect on the physiological state and behavior of
the young.

Apparently, however, under normal nesting conditions
no environmental factor is so detrimental that the young
are adversely effected permanently. Otherwise, the
Eastern Phoebe simply would be eliminated from those places

where it now nests.

 

SUMMARY

1. A five year investigation (1958-1962) of nestlings

to the Eastern Phoebe, Sayornis phoebe, was made in Isabella

 

County, Michigan, to determine if there was any relationship
between growth and develOpment of temperature regulation and
the environmental factors in the nesting areas.

2. Daily nestling growth measurements were obtained
of weight, total body length, feather length (dorsal,
ventral, tail, primary, primary covert, secondary, secondary
covert) of 25 first-brood young, one to 12 days old and 21
first-brood young, 12 to 14 days old, and 13, second—brood
young, one to 12, and 10, second-brood young, 12 to 14 days
old between 1958 and 1961. Additional measurements were
also made of down length at hatching on both of the above
brood groups.

3. The growth measurements showed a Significant dif-
ference in first- and second-brood young during the first
11 days of nestling life but both groups were approximately
the same size near the end of the nestling period.

4. The presence of large numbers of ectOparasites on
the second-broods in 1958 prompted an investigation of the
numbers of ectOparasites found on first? and second—brood

young in 1959 and 1960. Five randomly sampled young for

68

 

69

each day of age, 1 to 14 days, in first— and second-broods
for these two years Showed a significant increase on the
second-brood young.

5. In the 1958—1961 studies of normal—Sized broods
the fledging success of the first-brood nestlings was
63.4 per cent; of the second-brood nestlings, 62.1 per
cent.

6. The average fledging time difference for the
1958-1961 first- and second-brood young was 2.1 days (14.8
days for first—brood young; 16.9 days for the second—brood
young.)

7. The effects of cowbird parasitism were not investi-
gated in this study but 9.4 per cent of all nests were
parasitized.

8. The 15 (1-14 day old) first—brood and 10 (1-14
day old) second-brood young subjected to two hours of con-
trolled temperature environments in the laboratory Showed
a significant difference in their ability to regulate their
body temperatures in the 10°C. and 40°C. environments.
Fourteen day old second-brood young did only as well as
nine day old first-brood young in regulating their body
temperatures at the 10°C. environmental temperature. In
the 40°C. environments the second—brood young always regis-
tered higher body temperatures than the first—brood young.

9. Compared to the body temperatures recorded for

five adult phoebes subjected to identical controlled

70

temperature environments in the laboratory (35.4°C. in 10°C.
environments; 37.8°C. in 40°C. environments), the nestling
phoebe exhibited the poikilothermic condition for the first
ten days of its life. The breathing efficiency of these
young showed an increasingly greater improvement during

the first ten days of nestling life.

10. Gaping-reSponse laboratory experiments conducted
during 1960-1961 with 12 first— and l7vsecond-brood (one to
six day old) randomly selected young, showed no Significant
difference (among brood groups) in their gaping—reSponse
ability after shorter, one—half hour, 10°C., 25°C., and
40°C. controlled temperature exposures. There was a sig-
nificant difference in the number of gaping responses among
each brood group at each of the three different temperatures,
however, indicating that air temperature has a direct effect
on the gaping responsiveness of the young.

11. During 1961—1962, environmental data were collected
at three first-brood and three second-brood nests of this
species during the first 12 days of nestling life. One of
the first-brood nests contained four young. In the other
two first-brood nests and the three second-brood nests the
number of young was reduced to two, in order to have com-
parable data to analyze.

12. The size and nature of the adults' foraging areas
at the Six nests (three nesting locations) were determined

during 1959—1960, in order to obtain a random sample of the

71

arthropod pOpulations at all nesting locations in 1961—1962.
The average size of these three foraging areas, which were
all mature woods—openings, changed by only 7 per cent (the
maximum change was 18 per cent) during the four year period
when all areas were mapped. During 1961-1962 the average
size of the foraging areas at all three nesting locations
was 4,727 square meters. The greatest changes in the for-
aging areas occurred on days when very adverse weather
conditions prevailed (high winds and/or heavy rain).

13. The weather conditions within the foraging areas
studied fluctuated greatly during the total study period
(between May 24—July 9, 1961 and May l8-Aug. 8, 1962).
Daily air temperatures, rainfall (amount and duration),
relative humidity, light intensity (cloud cover), and wind
Speeds were recorded.

14. The kinds and densities of arthrOpodS were deter-
mined in all foraging areas during the 1961-1962 study
period by using randomly placed, wind-vane type, ”sticky-
board" insect traps. Ninety-eight per cent of all arthro-
pods sampled during the study period belonged to seven
orders (Diptera 60.2 per cent, ColeOptera 18.8 per cent,
Hymenoptera 10.0 per cent, Homoptera 4.5 per cent, Hemip—
tera 2.1 per cent, EphemerOptera 1.8 per cent, and Araneae
0.9 per cent). There were well marked seasonal fluctuations

in these orders during the study period.

72

15. The daily means Of the number and weights of
arthropods sampled Showed very strong correlations to
weather fluctuations during the total nesting study. High
positive correlation coefficients were found between mean
daily numbers of arthrOpods and mean daily air temperature
(r = + 0.82) and between mean daily numbers of arthropods
and mean light intensity (r = +0.91). An extremely high
negative correlation was found between mean daily numbers
of arthrOpods and mean daily wind Speeds (r = -0.98) and an
apparently Significant negative correlation (r = -0.55)
between mean daily numbers of arthrOpodS and mean daily
rain hours.

16. Data collected on the feeding activities of the
adults indicated that both adults feed the young approxi-
mately the same number of times during the day. The data
Show, however, that the non-brooding adult feeds the young
significantly more times in the early morning and that the
brooding adult feeds the young a significantly greater num—
ber of times before brooding begins.

17. All adult feeding was done in flight. 0f the 783
catches Observed, 52 per cent were made in Open air, 32 per
cent were made in foliage, and 16 per cent were made directly
above the ground. Although only 11 per cent of these Obser-
vations resulted in the author being able to follow the
adult to the nest, all appeared to result in a nest trip

after only one catch. It appeared, also, that the adults

73

caught whatever aerial arthrOpods were available rather than
showing any food preference for certain arthropod groups.

18. The average length of the feeding day at Six nests
was 14.4 hours. There was little variation in feeding day
length during the total nesting study except on days when
adverse weather conditions occurred early in the morning
or evening.

l9. Trips to the nest, presumably with food each time,
were recorded with a modified "itograph" recorder. The
correlations between mean daily trips to the nest and mean
daily numbers and weights of arthrOpodS present in the
foraging areas were extremely high (r = + 0.95 for the
former, r + +0.94 for the latter). There was a strong nega-
tive correlation (r = -0.73) between the mean daily number
of trips to the nest and the mean number of brooding periods
by the adults. The number of trips made to the four—brood
young nest was 70 per cent greater than the average number
of trips to the two-brood young nests.

20. Brooding behavior records indicated that the same
adult broods each night, but that the nightly non-brooding
adult may occasionally brood during the day. Brooding
periods and duration seem to be strongly related to the
weather factors (increasing during adverse conditions, de—
creasing during good conditions).

21. Nest desertion occurred at only three nests:

twice by interference while eggs were in the nest, once

 

74

possibly because the adults were prevented from brooding
the young during the day by the presence of an artificial
nestling in the nest.

22. The general growth of the young in the Six nests
where the nesting environment was intensively studied ap-
peared to be slightly more rapid during the first 12 days
than in the general growth studies in 1958—1961. In these
nests there appeared to be no great difference between
first- and second-broods from the standpoint of daily
growth or fledging time. This was possibly due to less
irritation from mites because of smaller broods. The fact
that the broods had been reduced to two young in itself
might also account for heavier average daily weight gains.

23. Correlation coefficients of the daily mean weight
gain of the young and the mean weather conditions indicated
that there was little direct relationship between the
weather conditions in the young's environment and the rate
at which the young gained in weight each day. The Slight
negative character of these coefficients suggested several
indirect environmental-young relationships, however. These
were: (1) possibly the adverse conditions were making smaller
arthrOpods less available, thus the larger ones, although
fewer in number, would be ”worth more” in weight—gain value;
(2) the changing behavior of the adult's feeding activities
during adverse weather might bring them into contact with

arthrOpodS having greater weight—gain value to the young;

 

75

(3) the lowered air temperature might be reducing the energy
expenditure of the young during adverse weather periods,
though, of course increased brooding during these periods
would offset this gain; and (4) probably it was a combina-
tion Of the above plus several factors still not investigated.
24. No factor in the environment of the nestling
Eastern Phoebe appears to be so detrimental that the young
fail to mature, otherwise the Eastern Phoebe would be elim—

inated from where it now nests.

 

LITERATURE CITED

ABBOTT, C. G. 1922. The friendly phoebe. Bird Lore, 24;
75-79.

BALDWIN, S. P. and S. C. KENDEIGH. 1932. Physiology of
the temperature of birds. Sci. Publ. Cleveland Mus.
Nat. Hist., 3; 1-196.

BARTHOLOMEW, G. A., JR., and W. R. DAWSON. 1954. Body
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181-187.

 

BEAL, F. E. 1912. Food of our more important flycatchers.
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BENT, A. C. 1942. Life histories of North American fly-
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BETTS, M. M. 1954. Experiments with an artificial nestl-
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. 1955. The behavior of a pair of Great Tits at
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CRAIG, C. C. 1953. On the utilization of marked specimens
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CUTHBERT, N. L. 1962. The birds of Isabella County,
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and F. C. EVANS. 1957. Relation of growth and
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76

77

DICE, L. R. 1956. Natural communities. Univ. of Mich.
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. 1958. Incubation and body temperatures in the
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GLICK, P. A. 1939. The distribution of insects, spiders,
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78

LACK, D. and E. LACK. 1952. The breeding behavior of the
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93

GRAPH I

Number of mites found on 20 randomly selected
nestling Eastern Phoebes from first— and second—
brood nests. Each point represents the mean num-
ber of mites on five randomly selected nestlings
during either 1959 or 1960.

NUMBER OF INDIVIDUALS

210

200

190

180

170

160

150

140

130

120

110

100

90

8O

70

60

50

40

30

20

 

94

—— 1959 First-brood Mites
--~—- 1959 Second-brood Mites

----- 1960 First-brood Mites
0° ° 0"" 1960 Second-brood Mites

DAYS AFTER HATCHING

 

12

 

13 14

95

GRAPH II

Mean difference in number of breaths per minute
between lO°C. and MO°C. two hour controlled temper-
ature exposures for 15 first-brood and 10 second—
brood young.

(10°C . -40°c . EXPOSURES)

MEAN DIFFERENCE IN NUMBER OF BREATHS/MIN.

 

96

 

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20 r- -___ Mean Value for 10 Second-brood Young
10 I I I I I I I L I I I I J

1 2 3 4 5 6 7 9 10 11 12 13 14

DAYS AFTER HATCHING

97

GRAPH III

The relationship between mean daily number
of arthropods and weather conditions in foraging
areas of 2-young broods of the Eastern Phoebe.
(Each point represents the mean values for the
first 12 days of nestling life at each nest.)

371$: figs 33 Q. 3sz

 

 

 

 

 

 

 

98

 

 

 

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99

GRAPH IV

The relationship between mean number of trips
to the nest daily, brooding behavior daily, and
daily environmental conditions in foraging areas
of 2—young broods of the Eastern Phoebe. (Each
point represents the mean values for the first 12
days of nestling life at each nest.)

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lOl

GRAPH V

The relationship between mean daily weight
gain of 2-young broods of the Eastern Phoebe,
adult attentiveness, and environmental factors.

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103

FIGURE 1

Diagram of temperature control chamber in cold
cabinet with air source, manometer, and position of
nest and young in chamber.

MANOMETER

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105

FIGURE 2

Method used to determine unknown area size of
adult Eastern Phoebe foraging areas.

2A.

2B.

Map of foraging area (reduced to 1/5
actual size) of adult Eastern Phoebes
at nest site No. 22 during 1961 and
1962, showing quadrat subdivisions for
random sampling insect populations.
Map is drawn to scale (each quadrat
equals 10 square meters) on larger
rectangle of known area size.

Map removed from larger rectangle for
weighing. The proportion between weight
of rectangle paper and the square area
that it represents equals the proportion
between the weight of the same map re-
moved from the same rectangle and its
(unknown) size.

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107

PLATE 1

Field weighing kit with Ohaus triple-beam balance
and plastic container for weighing young older than
none days.

108

 

109

PLATE 2

Field Tabulation Forms for recording and
tabulating growth measurements of young (reduced
4/5ths.).

2A. Daily field record.

2B. Growth measurement tabulation form.

llO

SPECIES “EST 30.

Location

Date

 

 

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Feeding Date (Interval and Duration)

2A

03HITHOLOJICAL RESEARCH: “3111151613 TABUIATION 3m
SPECIES MEASUREMENT OF

 

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lll

PLATE 3
Standardized Laboratory and Field Forms
(reduced A/5ths.).

3A. Temperature Regulation Experiment
Form

3B. Field Compilation Form

112

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3B

113

PLATE 4

Wind-vane type arthrOpod sampling instrument.

AA. Arthropod sampling board mounted on
tOp of 6' metal pole.

AB. Close-up of masonite board containing
"tree-tanglefoot” for trapping arthropods.

AC. Carrying case for masonite boards.

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115

PLATE 5

Trip recorder for recording the number
and duration of adult trips to the nest during
feeding hours.

5A. Hand-wound clock recorder opened
to show trip-record paper in place.

5B. Recorder closed during recording period.

116

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117

PLATE 6

Nestling platform cage with micro-switch
perch with electric lines going to trip recorder.

6A.

6B.

Nesting platform cage in place prior
to enclosing nest.

Nesting platform cage in use. Note
that micro-switch perch is even with
nest rim.

118

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119

PLATE 7

Four-hour cycle contact sensitive paper
for recording trips to the nest by adults at Nest
No. 62-17B on July 28, 1962 between 8:10 a.m. and
12:00 p.m. (33 trips) and between 4:00 p.m. and

7:50 p.m. (46 trips).

 

 

 

 

 

 

 

 

 

   

     

     

 

 

 

 

 

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121

PLATE 8

Artificial nestling used in an attempt to
collect food brought to the nest by the adults.

8A. Head of artificial nestling with metal
"mandibles" partly open, mounted on end
of a tube of stiff muslin.

8B. Artificial nestling with mandibles
closed, enclosed by nest on nesting
platform.

80. Front of nest platform showing arrangement
of micro-switch perch. Two six-volt
batteries are attached below.

122

 

  

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123

PLATE 9

Recorder arrangement fkm'continuously
measuring the temperatures at the bottom of
the nests.

9A. YSI laboratory recorder with dials
set in standardized fixed positions.

9B. YSI laboratory recorder and 12 volt
automobile battery power source. Note
wheatstone bridge arrangement in
circuit with 2, 6 volt batteries to the
left of the recorder. The D.C. to A.C.
converter is above YSI recorder.

12AL

..
.
.
~

 

9B

125

PLATE 10

Nest temperature records at Nest No.
62-17B on July 28, 1962, recorded on YSI
Laboratory Recorder contact-sensitive paper
which moved at the rate of one inch per hour.
Note the scale of temperature values at the
top of the left chart segment.

126

 

 

 

127

PLATE 11

Instrument and observation tent at
Nest No. 22A (circled with arrow). Note
electric lines to nest and insect sampling
board at far right.

PLATE 12

Hygrothermograph for obtaining 24 hour
continuous records of air temperature ( C.) and
relative humidity (%) in the foraging areas of
the adults.

128

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end: («urchumitu‘lza
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12

129

PLATE l3

Hygrothermograph record at Nest 62-17B on July 28, 1962.

130

 

131

PLATE 14

Growth photos of one day old nestling Eastern Phoebes
14A. Side View

14B. Ventral View

PLATE 15

Growth photos of 3 day old nestling Eastern Phoebes
15A. Side view

15B. Ventral View

132

 

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133

PLATE 16

Growth photos of nestling 5 day old Eastern Phoebes
16A. Side view

16B. Ventral view

PLATE 17

Growth photos of 10 day old nestling Eastern Phoebes
17A. Side view

17B. Ventral view

 

    

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135

PLATE 18

Growth photos of 15 day old nestling Eastern Phoebes.
18A. Side view of normal posture.

18B. Side View showing wing feathers extended
and feathers along ventral tract.

136

 

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18A

 

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