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NESTING SUCCESS AND CHICK SURVIVAL OF RUFFED GROUSE
(BONASA UMBELLUS) IN NORTHERN MICHIGAN

By

Michael A. Larson

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Fisheries and Wildlife

1998

ABSTRACT

NESTING SUCCESS AND CHICK SURVIVAL OF RUFFED GROUSE
(BONASA UMBELLUS) IN NORTHERN MICHIGAN

By

Michael A. Larson

Although much is known about the breeding and brooding behavior of ruffed
grouse (Bonasa umbellus) hens, relatively little is known about the fate of their nests and
chicks. This study was designed to document the reproductive parameters related to
nesting and quantify nest site characteristics by monitoring the nests of radio-marked
grouse hens in 1996 and 1997. Also, miniature radio transmitters were used to determine
the predispersal survival rate of grouse chicks.

First nesting attempts had a lower Mayfield survival rate (47.8%), a higher mean
clutch size (12.7 eggs), and higher egg hatchability (95.9%) than did second nesting
attempts (80.3% nest survival, 7.3 eggs/clutch, and 83.3% hatchability). The median
hatching dates were 10 June for first nests and 1 July for second nests. Nest site
characteristics were highly variable. Chick survival to 7 September was approximately
32%, and an estimated 2.25 juvenile grouse were recruited into the fall population for

each hen that began nesting the previous spring.

ACKNOWLEDGMENTS

Many people in several organizations helped with the completion of this research
project. I would like to begin by thanking Dr. Scott Winterstein, my major professor and
the principle investigator on the Michigan Ruffed Grouse Research Project, for his
guidance throughout my degree program. My other graduate committee members, Dr.
Rique Campa and Dr. Don Beaver, were valuable advisors as well. I would like to thank
my graduate student colleagues on the grouse project; Meg Clark for valuable assistance
throughout my program and Allison Gormley for helping to get me oriented in the
beginning. I am indebted to my interns who conducted most of the field work directly
related to this thesis. They were Steve Niemela, Mike VanAntwerp, Erynn Call, and Bill
Dodge. Many others helped with field work, especially Jeff Breuker, Ursula Rosauer,
Matt Carmer, and Andrew Larder.

Michigan Department of Natural Resources personnel helped with various aspects
of the project, especially Larry Robinson and Dan Soults from the Mio office, Bill Green
from the Roscommon office, and Tom Cooley from Rose Lake Wildlife Research Area.
United States Forest Service biologists Dave Regal and Phil Huber helped me gather
information about vegetation. Special thanks go to Dr. Kevin Kenow of the National

Biological Service in LaCrosse, Wisconsin, for taking the time to patiently teach me the

iii

transmitter implant procedure. Financial support was provided by the Michigan
Department of Natural Resources Wildlife Division through the Pittman-Robertson Act.
The Ruffed Grouse Society also provided funding.

Valuable personal support and encouragement were provided by Carrie Thorvig.
I cannot thank her enough for being there for me. Finally, my fellow graduate students in
the Department of Fisheries and Wildlife deserve the rest of the credit. They made MSU

life truly enjoyable.

iv

TABLE OF CONTENTS

 

 

LIST OF TABLES ............................................................................................................. vi
LIST OF FIGURES ......................................................................................................... viii
INTRODUCTION ............................................................................................................... l
OBJECTIVES ...................................................................................................................... 4
STUDY SITES ..................................................................................................................... 5
METHODS .......................................................................................................................... 8
Locating Nests ................................................................................................................. 8
Nest Sites ......................................................................................................................... 9
Nesting Parameters ........................................................................................................ 11
Chick Survival ............................................................................................................... 13
Population Modeling ...................................................................................................... 17
RESULTS .......................................................................................................................... 18
Locating Nests ............................................................................................................... l8
Nest Sites ....................................................................................................................... 19
Nesting Parameters ........................................................................................................ 39
Chick Survival ............................................................................................................... 48
Population Modeling ...................................................................................................... 55
DISCUSSION .................................................................................................................... 59
Nest Sites ....................................................................................................................... 59
Nesting Parameters ........................................................................................................ 64
Chick Survival ............................................................................................................... 68
Population Modeling ...................................................................................................... 71
MANAGEMENT IMPLICATIONS ................................................................................. 72
APPENDIX A: FALL-TO-SPRING SURVIVAL ........................................................... 74
APPENDIX B: ORIGINAL DATA .................................................................................. 83
LITERATURE CITED ...................................................................................................... 92

LIST OF TABLES

Table 1. Dominant overstory vegetation type of ruffed grouse nesting sites in

northern Michigan in 1996 and 1997. ........................................................................ 21
Table 2. Objects against which ruffed grouse positioned their nests in northern

Michigan in 1996 and 1997. ...................................................................................... 23
Table 3. Species of live tree or snag against which ruffed grouse positioned their

nests in northern Michigan in 1996 and 1997. ........................................................... 24
Table 4. Species of live tree or snag against which ruffed grouse positioned their

nests at the PRCSF study site in northern Michigan in 1996 and 1997 ..................... 26
Table 5. Species of live tree or snag against which ruffed grouse positioned their

nests at the HNF study site in northern Michigan in 1996 and 1997 ......................... 27
Table 6. Median nest site characteristics of ruffed grouse in northern Michigan in

1996 and 1997. ........................................................................................................... 37
Table 7. Nest initiation dates (day of the year from 1 January) of ruffed grouse in

northern Michigan in 1996 and 1997. ........................................................................ 41
Table 8. Hatching dates (day of the year from 1 January) of ruffed grouse in

northern Michigan in 1996 and 1997. ........................................................................ 44
Table 9. Clutch size of ruffed grouse nests in northern Michigan in 1996 and 1997. ...... 46

Table 10. Egg hatchability (%) of mfled grouse in northern Michigan in 1996 and
1997 ............................................................................................................................ 47

Table 11. Mayfield nest survival rates of ruffed grouse in northern Michigan in
1996 and 1997. ........................................................................................................... 49

vi

Table 12. Ending status and sources of m0rtality of ruffed grouse chicks in northern
Michigan during the summers of 1996 and 1997. ..................................................... 52

Table 13. Relative ruffed grouse chick production for every 100 females that
survived to begin nesting in northern Michigan in 1996 and 1997. .......................... 56

Table A1. Log rank comparison of Kaplan-Meier survival functions for the period
of 5 August to 15 May between areas open and closed to grouse hunting in

northern Michigan in 1993-1997 ............................................................................... 75

Table A2. Log rank comparison of Kaplan-Meier survival functions for the period
of 5 August to 15 May between study sites in northern Michigan in 1994-1997 ..... 81

Table A3. Kaplan-Meier survival rates for the period of 7 September to 1 May by
sex and age of ruffed grouse in northern Michigan in 1994-1997 ............................ 82

Table Bl. Original categorical data for ruffed grouse nest sites in northern
Michigan in 1996 and 1997 ....................................................................................... 83

Table B2. Original interval data for ruffed grouse nest sites in northern Michigan
in 1996 and 1997 ....................................................................................................... 85

Table B3. Original data for nesting parameters of ruffed grouse in northern
Michigan in 1996 and 1997 ....................................................................................... 87

Table B4. Original data for ruffed grouse chicks captured in northern Michigan in
1996 ........................................................................................................................... 89

Table B5. Original data for ruffed grouse chicks captured in northern Michigan in
1997 ........................................................................................................................... 9O

vii

LIST OF FIGURES

Figure 1. Map of Michigan counties indicating the location of the Huron National
Forest (HNF) and Pigeon River Country State Forest (PRCSF) study sites. .............. 6

Figure 2. Schematic drawings of externally sutured transmitters. .................................... 15

Figure 3. Proportion, by nesting attempt, of ruffed grouse nests oriented in each of
8 general compass directions from a solid object. ..................................................... 28

Figure 4. Proportion, by hen age, of ruffed grouse nests oriented in each of 8
general compass directions from a solid object. ........................................................ 29

Figure 5. Proportion, by nest fate, of ruffed grouse nests oriented in each of 8
general compass directions from a solid object. ........................................................ 30

Figure 6. Proportion, by nesting attempt, of ruffed grouse nest sites with a slope
aspect in each of 8 general compass directions .......................................................... 32

Figure 7. Proportion, by hen age, of ruffed grouse nest sites with a slope aspect in
each of 8 general compass directions. ........................................................................ 33

Figure 8. Proportion, by nest fate, of ruffed grouse nest sites with a slope aspect in
each of 8 general compass directions ......................................................................... 34

Figure 9. Distribution of ruffed grouse nest initiation dates in northern Michigan

in 1996 and 1997 ........................................................................................................ 40
Figure 10. Distribution of ruffed grouse hatching dates in northern Michigan in

1996 and 1997. ........................................................................................................... 43
Figure 11. Survival of ruffed grouse chicks in northern Michigan. .................................. 51

Figure 12. Survival of ruffed grouse chicks with different methods of transmitter
attachment in northern Michigan in 1996. ................................................................. 53

viii

Figure Al. Kaplan-Meier survival rates of ruffed grouse in 2 study sites in northern
Michigan for the fall-to-spring period in 1994-95 .................................................... 76

Figure A2. Kaplan-Meier survival rates of ruffed grouse in 2 study sites in northern
Michigan for the fall-to-spring period in 1995-96 .................................................... 77

Figure A3. Kaplan-Meier survival rates of ruffed grouse in 2 study sites in northern
Michigan for the fall-to-spring period in 1996-97 .................................................... 78

Figure A4. Kaplan-Meier survival rates of ruffed grouse in the Huron National
Forest study site for the fall-to-spring periods from 1994 to 1997 ............................ 79

Figure A5. Kaplan-Meier survival rates of ruffed grouse in the Pigeon River Country
State Forest study site for the fall-to-spring periods from 1994 to 1997 ................... 8O

ix

INTRODUCTION

The ruffed grouse (Bonasa umbellus) is the most widely distributed member of
the Tetraoninae in North America, occurring in at least 47 states and provinces (Gullion
1977, Cade and Sousa 1985). It is considered the most important small game resource in
9 of those political districts. Between 1970 and 1974, 63% of ruffed grouse taken by
hunters in North America were from Michigan, Minnesota, Ontario, and Wisconsin
(Gullion 1977). Currently, about 125,000 hunters pursue ruffed grouse in Michigan each
year (Winterstein et a1. 1995:24). Although the ruffed grouse is most popular as a game
bird, its presence in the forest is appreciated by hunters and non-hunters alike.

Much attention by wildlife researchers has been paid to the population dynamics
of grouse. Understanding major periodic fluctuations in grouse abundance, known as the
10-year cycle, and the effect of hunting pressure have been of special interest (Criddle
1930, Bump et a1. 1947, Palmer 1956, Marshall and Gullion 1965, Fischer and Keith
1974, Rusch et a1. 1984, Stoll and Culbertson 1995). Fall-to-spring survival plays a key
role in population fluctuations, but the importance of chick production and predispersal
survival have also been recognized (Gullion 1970, Smyth and Boag 1984). Although

much is known about the breeding and brooding behavior of grouse hens (Schladweiler

1965; Brander 1967; Barrett 1970; Maxson 1974a, b; Maxson 1978a, b), relatively little
is known about the fate of their nests and chicks.

Nesting success, including the percentage of eggs that hatch, may depend on the
quality of the nesting habitat. Various habitat components have been used to describe
grouse nesting sites. Nests are generally adjacent to a solid object and are only a short
distance from mature aspen trees and an opening (Bump et a1. 1947; Maxson 1974a,
19780; Gullion 1977). Relatively low densities of woody stems and herbaceous
undergrowth are valuable features of the nest site as well (Bump et a1. 1947, Gullion
1977, Maxson 1978a, Thompson et a1. 1987). Nest sites may be further characterized by
their distance from the nearest conifer tree and the aspect of the nest relative to other
objects or the slope of the ground (Bump et a1. 1947, Maxson 1974a, Thompson et a1.
1987).

Some ruffed grouse are believed to make 2 nesting attempts in the same breeding
season if their first nest is destroyed before incubation begins. The assumption of
renesting is often based on evidence of a secondary peak in hatching that occurs a few
weeks after the initial peak and usually involves notably smaller clutches (Cringan 1970,
Porath and Vohs 1972, Maxson 1978a). The second nesting attempt of a marked hen has
been documented in only 1 case (Barrett 1970).

A more complete understanding of grouse summer population dynamics has been
limited by traditional methods of investigation. The ratio of the number of juveniles per
adult male in the fall population is a common grouse recruitment index (Domey and

Kabat 1960). It is difficult, however, to quantify and account for the bias toward

juveniles in sampling procedures such as trapping and hunter harvest. Porath and Vohs
(1972) compared crude density from 15 July to crude density in early spring to measure
grouse production. Also, brood flush counts have been used to measure grouse chick
abundance (Ammann and Ryel 1963) and to estimate chick survival (Rusch and Keith
1971). Unfortunately, brood flush counts are dependent on several variable factors
(Healy et al. 1980) and have proven to chronically underestimate brood size in grouse
(Godfrey 1975, Kubisiak 1978). Apparent brood intermixing and the failure to account
for total brood loss may also render brood size estimates based on flush counts unreliable.
This study was designed to provide opportunities for determining the rates and
sources of predispersal mortality by marking individual grouse chicks with radio
transmitters. A direct measurement of chick survival, as opposed to an indirect
measurement or index, will lead to an improved year-round grouse population model.
This study also was intended to document nesting parameters, such as clutch size and
hatching dates, and nest site characteristics in northern Michigan for comparison with

published data from other areas of the upper Midwest and Great Lakes region.

OBJECTIVES

The specific objectives of this study were to:
1. quantify habitat attributes related to grouse nest site selection,
2. determine grouse nesting success and the hatchability of grouse eggs, and

3. determine the survival of grouse chicks from hatching through fall dispersal.

STUDY SITES

This study was conducted during the spring and summer months of 1996 and
1997 in the northern portion of the lower peninsula of Michigan. The primary site was in
the Maltby Hills region of the Huron National Forest (HNF). A second study site was
located in the Pigeon River Country State Forest (PRCSF). The sites were divided into 2
areas--one that was closed to grouse and woodcock hunting and another, similarly-sized
area that remained open to hunting under normal harvest regulations. Each of the 4 areas
covered approximately 100 km2 (Figure 1). The areas were designated as hunted or
unhunted for purposes not related to this study (see Clark 1996, Gormley 1996).

The HNF site is found in parts of Alcona, Oscoda, and Ogemaw counties (44° 32‘
N 1at., 83° 58‘ W long.). Stands of aspen (Populus spp.), sugar maple (Acer saccarinum),
red pine (Pinus resinosa), white pine (Pinus strobus), white cedar (Thuja occidentalis),
and oak (Quercus spp.) cover most of the area. The topography varies from nearly level
to steep (up to 40% slopes) at elevations between 300 m and 430 m. Temperatures range
from an average daily minimum in winter of -11 C to an average daily maximum in

summer of 26 C. The area receives an average of 73 cm of precipitation each year,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Map of Michigan counties indicating the location of the Huron National
Forest (HN F ) and Pigeon River Country State Forest (PRCSF) study sites.

about half of which occurs during the 120-day growing season (Johnson 1990). The
months of April and May at the HNF site were approximately 3.3 degree-days warmer
and received approximately 3.3 cm less precipitation in 1997 than in 1996 (Midwest.
Climate Cent., unpubl. data).

The PRCSF site is found in parts of Cheboygan, Otsego, and Montmorency
counties (450 11‘ N lat., 84° 26‘ W long). This site has vegetation and climate that are
similar to those at the HNF site due to their proximity. Major differences between the 2
sites include the lack of large oak stands, level to only undulating topography, and a
substantially shorter growing season of approximately 90 days at the PRCSF site (Tardy
1991). Detailed information about the forest structure, overstory vegetation, and grouse

habitat at both study sites can be found in Gormley (1996).

METHODS

Locating Nests

Nests for this study were found by approaching radio-collared grouse that were
located in the same place on 2 consecutive days during the nesting season. Therefore, it
was essential to have hens with functioning radio-collars in the spring. In August and
September of 1995 and 1996 grouse were captured using a modified version of the
Cloverleaf traps described by Domey and Mattison (1956). Traps were checked every
night between dusk and 3 hours after dark. Grouse in the traps were tagged with a
uniquely numbered Michigan Department of Natural Resources leg band. They were
aged as either hatch-year (<6 months old) or after-hatch-year (>12 months old) based on
the shape and condition of the ninth and tenth primaries (Hale et a1. 1954, Domey and
Kabat 1960, Godin 1960). The sex of each captured grouse was determined by the
number of spots on each rump feather (Roussel and Ouellet 1975). Grouse that weighed
>350 g and were uninjured were fitted with a bib-type radio transmitter (see Clark 1996,
Gormley 1996 for a detailed description of fall trapping and handling procedures). All

grouse were released about 10 m from the trap.

During the spring months of 1996 and 1997 attempts were made to replace the
radio-collars on surviving female grouse because the battery in the transmitters was not
expected to last more than 9 months. A nightlighting method was used early in the spring
(Huempfiier et a1. 1975). However, if a hen initiated incubation before the replacement of
her transmitter, attempts to recapture her were made during the day using a dip net.

In early May 1996, radio-collared grouse were monitored for drumming or nesting
behavior, in case any errors had been made in determining sex the previous fall. This was
not done in 1997 due to lack of success with this method. During both years all surviving
grouse were monitored as if they were hens to avoid the possibility of not locating the
nest of a radio-collared grouse simply because it was believed to be a male the previous
fall. In addition, all radio-collared grouse for which no nest had been found, regardless of
sex, were approached on foot and flushed during the week of 1 June in an attempt to

locate nests.

Nest Sites

The age and dominant overstory vegetation type of forest stands containing
located grouse nests were obtained from the Huron Shores and Mio district offices of the
US. Forest Service for the HNF site and the PRCSF headquarters. Many other attributes
of each nest site were analyzed after the nesting attempt was complete, and the hen was
no longer occupying the nest. The spatial relationship between nests and any solid
objects within 1 m were noted. The type and size of the objects were noted also,

including the species if the object was a tree or snag. The orientation of nests from solid

10

objects and the aspect of the ground slope 'were recorded as one of 8 general compass
directions.

The density of live woody stems 21 m tall was measured in a 10- x 10-m plot
centered on the nest with the comers being in the cardinal directions. Horizontal cover
was quantified from a uniform height (0.5 m) and distance in front of the nest using a 1-
m-tall profile board. Vertical cover at the nest, divided into ground cover (<15 m high)
and canopy cover (>1.5 m high), was quantified by estimating the percent cover in a 1- x
l-m plot and using a spherical densiometer, respectively. Distances from the nest to the
nearest opening, mature aspen tree (2 15 cm dbh), and conifer tree (21 m tall) were
measured also. An opening was defined as an area having no live woody stems and no
canopy cover for 2 5 m in one straight-line dimension.

Nest site characteristics were compared between years, study sites, and areas open
and closed to hunting to determine the appropriateness of combining data within those
categories. Then the combined data were used to compare the nest sites of first and
second nests, yearling and adult hens, and successful and unsuccessful nests.
Comparisons of the vegetation type and the type of object against which grouse nested
were made using Chi-square tests. Comparisons of nest orientation and slope aspect were
made using Fisher’s exact tests (Sokal and Rohlf 1995:730-736). Preliminary analysis of
nest site variables containing continuous data was conducted by assessing time series
plots, using principal components analysis of the correlation matrix (PCA) (Morrison
199013 13-331), and a multivariate analysis of variance (MANOVA) (Morrison 1990:200-

256). Then, in a few instances, pairwise comparisons were made with these data by

11

performing individual t-tests or Kruskal-Wallis tests (Ott 1993:792-795). The

significance of statistical tests described in this section was based on a = 0.05.

Nesting Parameters

Observed nest locations were marked in the field and on a map. Nests were
revisited between 6 and 18 hours after being located to determine if egg laying was
complete. This allowed for the prediction of a hatching date. Approximately 2 weeks
after being located nests were observed to determine the final clutch size, if it was not
known already. Nests were also approached if the hen was located off the nest or if the
hen’s radio signal indicated she was dead. This ensured that destroyed or abandoned
nests were found as soon as possible. Destroyed nests were investigated to determine the
type of predator that was responsible. All necessary precautions were taken to minimize
disturbance when approaching a nest to make direct visual observations. Incubating hens
were located daily using triangulation from up to 5 days prior to the predicted hatching
date until the eggs hatched. These triangulations were made from a distance of 30-100 m
from the nest. The initial brood size was determined by counting the number of eggs that
did and did not hatch. Renesting attempts were monitored in the same manner as first
nests.

Nest initiation was never observed, so the date had to be estimated using the
earliest known point in the nesting sequence. A known point occurred if 2 different
clutch sizes were observed, meaning that the nest was located during the egg-laying

period, or if the eggs hatched. To estimate the initiation date from a known point during

12

the egg-laying period 1.3 days for each egg were subtracted from the earliest date of
clutch size determination (Maxson 1974b). To estimate the initiation date from the
hatching date, 25 days for incubation and 1.3 days to lay each egg in the full clutch were
subtracted from the hatching date. Initiation dates and hatching dates were recorded as
the day of the year from 1 January. The Mayfield method was used to calculate nest
survival rates (Mayfield 1961).

Nesting variables were compared between first and second nests, years, study
sites, areas open and closed to grouse hunting, and yearling and adult hens. Two of the
nesting variables, clutch size and nest initiation date, were also compared between
successful and destroyed nests. Clutch sizes were compared using t tests. Egg
hatchability was analyzed in 2 different ways. First, individual eggs were treated as the
sampling units, and comparisons were made by testing for binomial proportions. Next,
egg hatchability was analyzed using each nest as a sampling unit. Egg hatchability rates
by nest were compared using the Wilcoxon rank sum test (Ott 1993:279-285). The
Wilcoxon rank sum test was used also to compare nest initiation dates. The ratio of the
difference in daily survival rates to the standard error of that difference (Z test) was used
to compare Mayfield nest success rates (Johnson 1979).

Twenty-seven pairwise comparisons were required to analyze these data. A
Bonferroni adjustment was made to control the experimentwise Type I error rate at 0.100
(Sokal and Rohlf 1995:240). Therefore, the significance of statistical tests described in

this section was based on a = 0.004.

13

Chick Survival

When broods were approximately 6 days old as many chicks as possible within a
brood were collected by hand. Broods were approached on foot by a team of 2-5 people.
Individual chicks were followed as the brood flushed. If fewer than 4 chicks were caught
immediately, the team remained at the flush site and searched for up to 15 minutes. At
the time of capture an attempt was made to estimate brood size for use in calculating a
chick survival rate for the first week after hatching. Captured chicks were placed in a 4.7
L plastic pail lined with soft vegetation and transported to the vehicle (<0.8 km).

At the vehicle the chicks were transferred to a large cardboard box containing a
hot water bottle at one end. The box was placed in the shade. Chicks were removed from
the box one at a time to be processed. First, they were weighed to the nearest 0.5 g in a
small plastic bag using a spring scale. Then they were positioned on a hot water bottle
and held by an assistant during transmitter attachment. Crystal controlled two stage
transmitters with a 12-week battery (model BD-ZG, Holohil Systems, Ltd., Carp, Ont.)
were used to individually mark chicks. Antennas were 17.5 cm long and had a total
diameter of approximately 0.5 mm.

Two different transmitter attachment procedures were used. In the first procedure
the transmitter was implanted just beneath the skin in the interscapular region (Korschgen
et a1. 1996). Stainless steel tubes were used to thread the antenna from an incision at the
base of the neck to an exit site just above the tail. Then the antenna was used to pull the
transmitter into place, and the neck incision was sutured closed with 1-2 mattress stitches.

Implanted transmitters weighed 1.25 g and were 16- x 8- x 5-mm in size.

14

In the second attachment procedure transmitters were attached externally by
sutures to the interscapular region. Transmitters attached by this method were fitted by
the manufacturer with 2 tubes for the passage of suture material. Both tubes were
positioned transversely on the ventral surface of the transmitter--one at the anterior end
and one at the posterior end. External transmitters weighed 1.33 g and were slightly
longer than the implanted transmitters (18 mm). Unwaxed dental floss was passed
through each tube and then under approximately 5 mm of the chick’s skin. The points
where the 2 sutures were passed under the skin were slightly closer together than the
tubes on the transmitter to allow for significant chick growth before the sutures would
pull out (Figure 2). Livestock identification tag cement (Nasco, Fort Atkinson, Wis.) was
applied to the ventral surface of the transmitter to secure it in place until the sutures
healed. Each suture loop was tied with a square knot. A small amount of Krazy Glue
was then applied to the knots.

In 1996, each transmitter attachment procedure was used an approximately equal
number of times in each brood. In 1997, only the external suture technique was used.
Radio-marked chicks were returned to their brood as soon as possible. The brood was
flushed on the return visit so that the captured chicks could be placed directly with the

unmarked chicks.

15

Figure 2. Schematic drawings of externally sutured transmitters.

A. Dorsal view of suture material being passed through the tubes and under the skin
before the transmitter is flipped over into the proper position (dashed outline).

B. Lateral view of a 6- to 8-day-old chick with an external transmitter.

C. A 10-week-old chick showing that the suture points are allowed to grow apart
longitudinally.

16

 

 

Figure 2. Schematic drawings of externally sutured transmitters.

17

Radio-marked chicks were located by triangulation 3-6 times per week. When a
chick died its remains were collected and sent to a Department of Natural Resources
laboratory. The results of a necropsy, the condition of the transmitter, and predator signs
at the collection site were used to determine the cause of mortality. A chick was
presumed to be dead if it was not with its hen. A marked chick in a brood whose hen did
not have a functioning radio-collar was presumed to be dead if it was not with other
marked brood mates or if it was in the same place where it was last located.

Survival probabilities for the radio-marked grouse chicks were calculated using
the Kaplan-Meier Product Limit estimator. Survival probabilities were compared
between years and between chicks with implanted transmitters and those with external
transmitters using the log-rank test (Pollock et a1. 1989).

All capturing, handling, and marking procedures were reviewed and approved by

the All-University Committee on Animal Use and Care (AUF # 10/96-149-00).

Population Modeling

The nest survival rate, clutch size, egg hatchability, and chick survival rate were
multiplied to give an estimate of grouse recruitment into the fall population relative to the
number of hens that survived to nest the preceding spring. The grouse production data
from this study were combined with the sex-specific fall-to-spring survival rates of
grouse populations at the HNF and PRCSF sites from 1993 to 1997 (S. R. Winterstein,
Mich. State Univ., unpubl. data) to develop a descriptive year-round population model for

ruffed grouse in northern Michigan.

RESULTS

Lopating Nests

Recapturing hens in the spring was conducted only at the HNF site. Four hens
were successfully nightlighted in 1996, and 4 were recaptured on their nests in 1997. All
hens at both sites probably attempted to nest. For both years combined at the HN F site
nests were located for 22 of the 29 grouse that were identified as females at trapping the
previous fall and that were alive after 1 May. Only 2 of the 7 for which no nest was
located survived past 12 May, and they may have been misidentified at trapping or had
their nests destroyed early in the egg-laying period before they could be located. Nests
also were located for 4 of 10 grouse that survived to 1 May but whose sex was previously
unknown. No nests, however, were located by flushing radio-collared grouse during the
week of 1 June.

Nests were located for 10 of the 20 grouse hens at the PRCSF site that were alive
as of 1 May. Nests may not have been located for the other half of the hens for several
reasons. Five of the hens for which no nest was located died before 27 May and may

have been killed before they were able to begin a nest. Others may have had their sex

18

l9

misidentified or had their nest destroyed before it could be located. Also, nest search
effort was not as high and search methods varied slightly at the PRCSF site.

A total of 41 grouse nests were located during the study, 12 in 1996 and 29 in
1997. Two nests in 1996 and 4 in 1997 were renesting attempts. One of the first nests in
1997 did not belong to a radio-collared hen and is not included in the analysis of nesting
and reproductive success parameters because only its fate was determinable. However,
this nest is included in the nest site analysis below. A different nest is included in the
analysis of nesting and reproductive parameters but not in the analysis of nest sites, so the
total sample size in both data sets is 40 nests. First nests were 7-33 days old when they
were located. The mean age of first nests at the time of location was 19 days, which
corresponds to the second or third day of incubation. All second nests were located

within 10 days of initiation.

Nest Sites

Nesting habitat varied greatly among hens. Forest stands containing marked
grouse nests were of many types and were between 3 and 82 years old. Nest sites had
stem densities between 1300 stems/ha and 30,200 stems/ha (median = 5900 stems/ha),
had horizontal cover ranging from 5% to 100% at both 5 m (mean = 45%) and 15 m
(median = 85%) from the nest, had ground cover between 15% and 100% (mean = 53%),
and had canopy cover between 51% and 99% (median = 90%).

Grouse nests were located in 11 different types of dominant overstory vegetation.
Due to the small sample of nests (n = 40) the types were combined into the following 3

major categories: 1) aspen (Populus spp.), which contained enough marked nests to

20

warrant its own category, 2) other deciduous types, which includes northern hardwoods
[mostly maple (Acer spp.)], oak (Quercus spp.)/hickory (Carya spp.), oak, and lowland
brush, and 3) conifers, which includes jack pine (Pinus banksiana), jack pine/oak, red
pine (P. resinosa), white pine (P. strobus), and swamp conifer. One of the original 11
vegetation types was grass/opening. The 1 nest located in that type was excluded as an
outlier for this variable. The vegetation type classification was not indicative of the
actual nest site, which was in an area containing trees and shrubs near the edge of the
grass/opening. Similar numbers of nests were located in aspen and conifer types
(approximately 35-40% of nests each), with only slightly fewer nests in other deciduous
types (approximately 25% of nests). The proportion of nests in each category of
overstory vegetation was similar between years, sites, areas open and closed to hunting,
first and second nests, yearling and adult hens, and successful and unsuccessful nests
(Table 1).

All nests were positioned against 1 of 5 objects--a live tree, a snag (standing dead
tree), a stump, a log, or a branch laying on the ground. These objects were combined into
the following 3 categories to reduce the degree to which the assumption of minimum
expected values for the Chi-square test would be violated: 1) live trees, 2) other erect
objects, which includes snags and stumps, and 3) objects laying on the ground, which
includes logs and branches. Over 60% of nests were positioned against 1 or more live
trees. The other nests were divided almost equally between the other 2 categories. The
proportion of nests in each category was similar between years, sites, areas open and

closed to hunting, first and second nests, yearling and adult hens, and successful and

21

Table 1. Dominant overstory vegetation type of ruffed grouse nesting sites in northern
Michigan in 1996 and 1997.

 

 

Other X2 Test
Aspen deciduousa Coniferb statistic° P-valued
Year
1996 4 2 5 0.655 0.73
1997 9 7 8
Site
HNF l 1 6 9 1.174 0.57
PRCSF 2 3 4
Area
open 9 6 7 0.734 0.70
closed 4 3 6
Nesting attempt
first 12 8 11 0.381 0.83
second 1 1
Hen age‘=
adult 6 3 6 0.307 0.86
yearling 6 5 7
Nest fate
successful 1 0 7 8 0.993 0.62
unsuccessful 3 2 5

 

a This category includes maple, oak, oak/hickory, and lowland brush.

b This category includes jack pine/oak, jack pine, red pine, white pine, and swamp
conifer.

° Test of independence between rows and columns. For example, there is no relationship
between year and dominant overstory vegetation type.

d Significance based on P < 0.05.

° Two hens were of unknown age.

22

unsuccessful nests (Table 2). The only marginally significant result was that no second
nests were positioned against an object laying on the ground, but there were only 6 nests
in that sample, which makes interpretation tenuous.

The kind of tree or snag against which a grouse positioned its nest was identified
at least to its genus. The 1 1 different kinds of trees and snags were combined into the
same 3 categories that the dominant overstory vegetation types were. Aspens, as above,
have their own category. The “other deciduous trees” category includes maple, oak,
birch (Betula spp.), beech (F agus grandifolia), and ironwood (Carpinus caroliniana).
The “conifer” category includes balsam fir (A bies balsamea), jack pine, red pine, white
pine, and white cedar (T huja occidentalis). There were 10 nests associated with each of
the 3 categories. Unexpectedly, tests indicated that years were significantly different
(Table 3). Sites also were significantly different, but this was probably due to the
differences in the proportions of various overstory vegetation types at the 2 study sites
(Gormley 1996224). The HNF is known to have a much higher proportion of coverage in
aspen and other deciduous types, and the PRC SF is known to have a much higher
proportion of conifer coverage. This difference in vegetation composition between sites
contributes to the difference in object selection between years. In 1996 approximately
equal numbers of nests were located at each site. In 1997, however, two-thirds of nests
were at the HN F site, leading to many more nests positioned against aspen trees in that
year. The study site difference also was evident in the number of nests located in the

different dominant overstory vegetation categories, even though the comparison did not

23

Table 2. Objects against which ruffed grouse positioned their nests in northern Michigan
in 1996 and 1997.

 

 

Live Snag or Log or X2 Test
tree stump branch statistica P-valueb
Year
1996 10 1 1 3.180 0.22
1997 15 6 7
Site
HNF 17 4 7 1.765 0.43
PRCSF 8 3 1
Area
open 17 4 3 2.378 0.32
closed 8 3 5
Nesting attempt
first 22 4 8 5.849 0.055
second 3 3 0
Hen agec
adult 13 4 2 1.595 0.46
yearling 1 1 3 5
Nest fate
successful 20 4 4 3.265 0.21
unsuccessful 5 3 4

 

a Test of independence between rows and columns. For example, there is no relationship
between year and type of object.

° Significance based on P < 0.05.

c Two hens were of unknown age.

24

Table 3. Species of live tree or snag against which ruffed grouse positioned their nests in
northern Michigan in 1996 and 1997.

 

 

Other X2 Test
Aspen deciduous2| Conifer° statisticc P-valued
Year
1996 0 5 6 8.900 0.013
1997 10 5 4
Site
HNF 9 8 4 6.667 0.038
PRCSF 1 2 6
Area
open 7 6 8 0.952 0.63
closed 3 4 2
Nesting attempt
first 9 10 7 4.038 0.146
second 1 0 3
Hen age°
adult 3 6 6 1.768 0.43
yearling 6 4 4
Nest fate
successful 7 9 7 1 .491 0.48
unsuccessful 3 1 3

 

a This category includes maple, oak, birch, beech, and ironwood.
This category includes fir, jack pine, red pine, white pine and cedar.
° Test of independence between rows and columns. For example, there is a relationship
between year and type of tree or snag.
° Significance based on P < 0.05.
c One hen was of unknown age.

25

reveal a statistically significant difference (Table 1). Over 40% of nests at the HNF site
and only about 20% of nests at the PRCSF site were located in aspen stands.

When data were separated by study site the tree and snag species did not appear to
differ by year at the PRCSF. Therefore, the comparisons of first and second nests,
yearling and adult hens, and successful and unsuccessful nests were investigated within
that site but with years combined (Table 4). There were no obvious differences. At the
HNF site years still appeared to be different, so the last 3 comparisons were investigated
within years at that site (Table 5). No obvious differences were apparent at the HNF site
either.

The orientation of grouse nests relative to the object against which they were
positioned did not differ by year, site, or areas open and closed to hunting (Fisher’s exact
test, P > 0.7 for all 3 comparisons). Nests were found in all 8 general compass directions.
As expected, most first nests were found on the south and east sides of an object where
they would receive direct sunlight in the morning and throughout much of the day (Figure
3). No second nests were found in these directions, but exposure to sunlight for heat
would not be as important later in the spring when second nests are begun, and the
difference between nesting attempts was not significant (P = 0.082). Nest orientation
also was similar between yearling and adult hens (Figure 4, P = 0.986) and successful and
unsuccessful nests (Figure 5, P = 0.222).

More than half of the nests were located on level ground. The aspect of the
ground at nest sites that were located on a slope did not differ between years, sites, or

areas open and closed to hunting (Fisher’s exact test, P > 0.5 for all 3 comparisons).

26

Table 4. Species of live tree or snag against which ruffed
grouse positioned their nests at the PRCSF study site in
northern Michigan in 1996 and 1997.

 

Other
Aspen deciduousa Conifer°

 

Year
1996 0 1 4
1997 1 1 2
Nesting attempt
first 1 2 3
second 0 0 3
Hen age
adult 1 2 5
yearling 0 0 1
Nest fate
successful 0 2 5
unsuccessful 1 0 1

 

a This category includes only maple.
This category includes fir, white pine, and cedar.

27

Table 5. Species of live tree or snag against which ruffed grouse positioned their nests at
the HNF study site in northern Michigan in 1996 and 1997.

 

Other
Aspen deciduousa Conifer°

 

Year
1996 0 4 2
1997 9 4 2
1996
Nesting attempt
first 0 4 2
second 0 0 0
Hen age
adult 0 3 1
yearling 0 1 1
Nest fate
successful 0 3 1
unsuccessful 0 1 1
1997
Nesting attempt
first 8 4 2
second 1 0 0
Hen agec
adult 2 1 0
yearling 6 3 2
Nest fate
successful 7 4 1
unsuccessful 2 0 1

 

a This category includes maple, oak, birch, beech, and ironwood.
b This category includes jack pine and red pine.
° One hen was of unknown age.

28

N
0.3 . 5
NW \ “5 NE
\ i9 /
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\ c:
\\ {:3 ,//
I 5' I'
\ 0.1 A =- /
\x\ //
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/ / \
//A/° + \\\
\
\.
\
. A \\
sw / SE
S Nesting attempt
AFirst
lSecond

Figure 3. Proportion, by nesting attempt, of ruffed grouse nests oriented in each of 8
general compass directions from a solid object. Proportions may not sum to 1 because
orientation was not recorded for 4 nests that were positioned under an object. P = 0.082
for Fisher’s exact test.

0.2

NW

\\
0.1
.,\
l
w _____ —-——¢— 4— - - 0a».
.///
/I/
//
SW /

I
Proportion of nests of each type

29

Hen age
A Yearling
I Adult

Figure 4. Proportion, by hen age, of ruffed grouse nests oriented in each of 8 general
compass directions from a solid object. Proportions may not sum to 1 because
orientation was not recorded for 4 nests that were positioned under an object. P = 0.986

for Fisher’s exact test.

30

N
Q)
G.
b
J:
0.2 - 8
NW “5 NE
\ 3 //
. g /’//
., \ A ‘5 ,/
.5. l’
0.1 - E
. I 3.
\K. a. .’A
X\ /'/
\\ /,K/
,/
W —— — - A — ——— — —0.0-—1)-<-~~- — — —-— It +— * ~ E
/‘A \\.
/ ’ A.
)/ \K\
/< x
/ I \\

\
swIr ‘ SE
A

Nest fate
S ASuccessful

I Unsuccessful

Figure 5. Proportion, by nest fate, of ruffed grouse nests oriented in each of 8 general
compass directions from a solid object. Proportions may not sum to 1 because
orientation was not recorded for 4 nests that were positioned under an object. P = 0.222
for Fisher’s exact test.

31

Most nests on slopes had at least some southerly or easterly exposure, and more were
sloped to the south-east than any other direction. First and second nests (Figure 6, P >
0.999), nests of yearling and adult hens (Figure 7, P = 0.558), and successful and
unsuccessful nests (Figure 8, P = 0.094) also did not differ according to slope aspect.

No trends over time were detected in most of the nest site variables containing
continuous data. However, the values for horizontal and ground cover were markedly
higher at the PRCSF site in 1996 than in 1997 or in either year at the HNF site (variances
were still similar). This difference was not sufficiently large to elicit a significant overall
year effect in the MAN OVA for the PRCSF site, but the cause is obvious. The values of
these variables change dramatically as herbaceous vegetation continues to emerge in the
summer. Nest site data at the HNF study site were collected between 11 June and 15
June in 1996 and between 11 June and 3 July in 1997. Data were collected on nest sites
at the PRCSF study site on 7 July 1997, which was similar to the timing of vegetation
sampling at the HNF site, but not until 7 August in 1996.

Only 28 nests could be used for principal components analysis when the stand age
and diameter of nest tree variables were included because they contained missing data, so
PCA also was run once without using the diameter variable and once without using either
the stand age or diameter variables. When the diameter of the nest tree was included it
did not appear to contribute much to the variability in the significant principal
components, so emphasis was placed on the latter 2 PCA trials. They yielded similar
results. Starting with 9 and 8 variables, the 2 trials accounted for 83% and 87% of the

variability in the first 5 principal components, respectively. Inspection of the eigen

32

N
0.2 o
O.
3‘
.C
0
CG
0
8—
NW 1 o
A\ m
:2
Q)
\ C:
\\ c...
o
0.1 - .5
1:
.1 g
’ E
. A ‘3-

._\\

.\\ /

W W 40- x—

A

/,
A
/
//’-
SW\
S

NE

 

Nesting attempt

A First
. Second

Figure 6. Proportion, by nesting attempt, of ruffed grouse nest sites with a slope
aspect in each of 8 general compass directions. Proportions do not sum to 1 because
slope aspect was not recorded for 23 nests that were on level ground. P > 0.999 for

Fisher’s exact test.

33

 

 

N
o
o.
b
‘5
0.2 - 3
NW 1 “5 NE
\ :9
\ ‘ 8 ///
\\I C ‘1/
.\\\ “a //,\<

.S /

0.1 A g
\ o.
\\ \ E ‘
)(\ /
\\ /
\\
\ ‘I/
w - —-.—- »—-—oax~~—a———+ - E

/’/ l \

/ \

SW SE

Hen age

A Yearling
I Adult

Figure 7. Proportion, by hen age, of ruffed grouse nest sites with a slope aspect in
each of 8 general compass directions. Proportions do not sum to 1 because slope
aspect was not recorded for 23 nests that were on level ground. P = 0.558 for Fisher’s
exact test.

34

N
8.
29
.C."
0.2 - §
NW “5 , NE
\\ ,3 /
\ ' Q) ’//
s: /‘ I
\ .2 "
\ \ 0 1 _' t ///
“ é ///
y\\ A O- I/IY
‘ k. /’ I
W ——— «e *— _¥ - -— ———100’5I;>-:fl— — ——A—— _ —-- w-———— E
/ A \
” A \\
// \A
\
\
/ w \
/
/‘ \\
/ \
swi \ SE
Nest fate
S A Successful

I Unsuccessful

Figure 8. Proportion, by nest fate, of ruffed grouse nest sites with a slope aspect in
each of 8 general compass directions. Proportions do not sum to 1 because slope
aspect was not recorded for 23 nests that were on level ground. P = 0.094 for Fisher’s
exact test.

35

vectors indicated that stand age, horizontal cover from 15 m, and canopy cover
contributed most to the variability in the data, and horizontal cover from 5 m never
contributed much variability to the first 5 dimensions. Biplots were constructed from the
first 3 dimensions, which accounted for >60% of the variability. When the independent
variables (year, site, area, nesting attempt, hen age, nest fate) were used as data labels no
groupings were evident, indicating that the pairwise groupings were not separated along
the dimensions of highest variability.

Multivariate analysis of variance also is sensitive to missing data, so 2 separate
MANOVAs were used to analyze the stand age and diameter of nest tree variables and
the other 8 variables containing continuous data. The data were fit to a model containing
the independent variables of year, site, and area (open vs. closed to hunting), as well as
the 2-way interactions among them. There were not enough degrees of freedom to test
for a 3-way interaction. The overall effect of the site x area interaction was significant (P
= 0.0282). There were not enough degrees of freedom to test for any interactions among
year, site, and area when running a MAN OVA for the stand age and diameter of nest tree
variables, but the overall effect of both site and area were significant (both P < 0.003).
Visual inspection of graphs and individual AN OVAs indicated that 2- or 3-way
interactions were present in nearly all of the variables.

Next, an additional set of MANOVAs were conducted for the HNF and PRCSF
sites separately. This was done to reduce the site x area interaction to an overall area

effect and for the intuitive reason that there were known differences in stand-level

36

vegetation between the HNF and PRCSF sites (Gormley 1996). In general, most forest
stands at the PRCSF site were older and contained larger trees at lower densities than the
stands at the HNF site (Table 6). A better developed understory in the more mature forest
at the PRCSF site also resulted in more horizontal and ground cover there. The

MAN OVA models contained the variables year and area as main effects, and there were
sufficient degrees of freedom to test for a year x area interaction at the PRCSF site only.
None of these overall effects were significant at the HNF site (all P > 0.135) or the
PRCSF site (all P > 0.650). Therefore, continuous nest site data were combined between
years and areas within sites.

These combined data were used in MANOVAs for the model containing the
independent variables of nesting attempt, hen age, and nest fate. Within sites there were
not sufficient degrees of freedom to test for interactions. The overall main effects were
not significant at either site. However, a few of the individual AN OVAs indicated
possible differences between a few groups. The subsequent pairwise tests for these
possible differences were all significant. At the HNF site first nests appeared to be much
closer to the nearest aspen tree (Kruskal-Wallis test, P < 0.001 ), but there was only one
second nest in the comparison (Table 6). At the PRCSF site second nests were positioned
against larger trees than first nests (t-test, P = 0.0311), and unsuccessful nests were
located much closer to the nearest aspen tree than successful nests (Kruskal-Wallis test, P

< 0.001).

37

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39

Nesting Parameters

The date of initiation was determined for 33 nests (Figure 9). It ranged from 26
April to 4 June. There was no overlap between the initiation dates of first and second
nests. The median date of first nest initiation was 1 May (day 121 from 1 January). This
was similar between years, sites, areas open and closed to hunting, yearling and adult
hens, and successful and destroyed nests. However, nesting did appear to begin about 4
days earlier in 1997 than in 1996, but this difference was not statistically significant (P =
0.038; experimentwise a = 0.10, with Bonferroni adjustment individual significant a =
0.004) (Table 7). When the 4 first nests from the PRCSF site for which the initiation date
was known were removed the difference in initiation dates between years at the HN F site
was only about 2 days. The possible earlier nesting in 1997 may be attributable to the
warmer, drier weather during the month of April in that year (see Study Sites section
above).

Ten first nests were destroyed. Two of these nests were not observed. They were
presumed to have been destroyed before they could be located because the only nests
located for 2 of the hens were initiated relatively late and had relatively small clutch sizes
and were, therefore, presumed to be second nesting attempts.

Of the 5 yearling hens that survived the destruction of their first nest, 2 made a
second attempt at nesting that same year. All 4 of the adult hens that could have renested

did. One of the 10 hens was of unknown age.

Number of nests

40

12 _
1 I
2 D

median = 29 May

W 5. .

I40 150 160

 

 

Day of the year

Figure 9. Distribution of ruffed grouse nest initiation dates in northern Michigan
in 1996 and 1997.

41

Table 7. Nest initiation dates (day of the year from 1 January) of ruffed grouse in
northern Michigan in 1996 and 1997. Day 121 is 1 May.

 

First nesting attempts

Second nesting attemptsal

 

 

n median test statisticb P-valuec n median

Year

1996 9 122.0 166 0.04 2 147.5

1997 18 118.5 4 149.5
Site

HNF 23 121.0 52 >>0.10 1 148.0

PRCSF 4 119.5 5 151.0
Area

open 20 120.5 106 >>0. 10 1 155.0

closed 7 123.0 5 148.0
Nesting attempt

first 27 121.0 183 <<0.0l

second 6 149.5
Hen aged

adult 12 121.0 0.786 0.44 4 151.0

yearling 14 120.5 2 146.5
Nest fatef

successful 23 120.0 41 0.10 5 148.0

destroyed 2 124.5 1 15 1 .0

 

a No statistical comparisons were made between groups of second nests.

b Wilcoxon rank sum T.

c Significance based on P < 0.004 (see Methods for Bonferroni adjustment).

d One hen was of unknown age.
‘ A 2 statistic was used because both n, > 10.
f Two abandoned nests were not included.

42

Three of the hens that could have renested but did not had been incubating for 2 6,
2 10, and 20 days, respectively, when their first nest was destroyed. The fourth hen
had not begun incubating her first nest. Two of the hens that did attempt a second nest
also had not begun incubation when their first nest was destroyed. The same is likely true
for the 2 presumed first nests. The other 2 hens that attempted second nests had been
incubating for 2 9 and 213 days, respectively, when their first nest was destroyed.

The date of first nest destruction for hens that subsequently attempted a second
nest ranged from 22 May to 28 May but was perhaps as early as 15-20 May for the
presumed first nests. Two of the hens that did not attempt a second had their nests
destroyed during the same time period. The other 2 nests for which there were no second
attempts were destroyed during the first week of June. Second nests were initiated 3 to 6
days after the destruction of the first nest. The median date of second nest initiation was
29 May (day 149) (Figure 9).

Hatching dates of the 28 successful nests ranged from 4 June to 3 July (Figure 10,
Table 8). There was no overlap in hatching dates between first and second nests. The
median hatching date for first nests was 10 June (day 161). The median hatching date for
second nests was 1 July (day 182). Hatching dates were similar between years, sites,
areas open and closed to hunting, and yearling and adult hens. They were not compared
statistically because they were highly correlated with initiation dates (r = 0.98), for which
there was only one significant difference (first versus second nests), and they were more
similar between categories than initiation dates. Conducting formal statistical tests was

unnecessary and only would have inflated the overall Type I error rate.

Number of nests

43

12 — median=10June :

Nesting attempt
1 I
2 D

median = 1 July

 

J-ID---

 

 

145 155 165 175 185 195
Day of the year

Figure 10. Distribution of ruffed grouse hatching dates in northern Michigan in
1996 and 1997.

44

Table 8. Hatching dates (day of the year from 1 January) of ruffed grouse
in northern Michigan in 1996 and 1997. Day 161 is 10 June.

 

First nesting attempts Second nesting attempts

 

 

 

n median n median

Year

1996 6 162.0 2 179.5

1997 17 161.0 3 182.0
Site

HNF 19 161.0 1 182.0

PRCSF 4 161.0 4 180.5
Area

open 16 161.0 1 185.0

closed 7 161.0 4 179.5
Nesting attempt

first 23 161.0

second 5 182.0
Hen age

adult 12 162.0 3 184.0

yearling 11 160.0 2 179.5

 

45

The duration of the incubation period was determined for 5 nests. Three first
nests had incubation times of 24, 25, and 27 days for clutches of 13, 13, and 14 eggs,
respectively. The 2 second nests had incubation times of 21 and 26 days for 8 and 7 egg
clutches, respectively.

Full clutch size was determined for 30 first nests (Table 9). The mean was 12.7
eggs. This was significantly higher than the mean of 7.3 eggs in the 6 second nests. The
95% confidence interval for the difference in clutch size between first and second nests is
4.0 to 6.8 eggs. Clutch sizes were similar between years, study sites, open and closed
areas, yearling and adult hens, and successful and destroyed nests.

Egg hatchability also was significantly higher in first nests than second nests
(Table 10). Whereas 95.9% of the eggs in the 23 successful first nests hatched, only
83.3% of the eggs in the 5 successful second nests hatched (P < 0.002). This difference
in hatchability is also evident when nests are used as the sampling units, although at a
lower level of significance (P = 0.020). The proportion of successful nests experiencing
100% egg hatchability was 83% for first nests and 20% for second nests. Egg
hatchability was significantly higher in open areas than closed areas when eggs were the
sampling units (P < 0.003) but not when nests were the sampling units (P > 0.1). The
significant difference between areas is due entirely to a first nest in the closed area of the
HNF site in which only 5 of 13 eggs hatched. This nest was only 2 m from a forest road
that experienced heavy traffic from logging trucks during the 2 days prior to hatching.
All of the eggs from the other 6 successful first nests in closed areas hatched, which

explains the insignificant result when nests were analyzed. If the disturbed nest were

46

Table 9. Clutch size of ruffed grouse nests in northern Michigan in 1996 and 1997.

 

First nesting attempts Second nesting attemptsa

 

 

 

n mean SEb (statistic P-valuec n mean SEb

Year

1996 9 12.33 0.41 -0.90 0.378 2 8.00 0.00

1997 21 12.90 0.38 4 7.00 0.41
Site

HNF 23 12.70 0.25 -0.23 0.819 1 7.00

PRCSF 7 12.86 0.99 5 7.40 0.40
Area

open 20 12.85 0.33 -0.56 0.580 1 8.00

closed 10 12.50 0.58 5 7.20 0.37
Nesting attempt

first 30 12.73 0.29 8.01 <0.001

second 6 7.33 0.33
Hen aged

adult 14 12.86 0.44 -O.31 0.758 4 7.75 0.25

yearling 15 12.67 0.42 2 6.50 0.50
Nest fate"

successful 23 12.87 0.28 -0.82 0.420 5 7.20 0.37

destroyed 5 12.20 1 .28 1 8.00

 

‘ No statistical comparisons were made between groups of second nests.

b Standard error.

° Significance based on P < 0.004 (see Methods for Bonferroni adjustment).
d
One hen was of unknown age.

° Two abandoned nests were not included.

47

Table 10. Egg hatchability (%) of ruffed grouse in northern Michigan in 1996 and 1997.
Numbers are for first nests unless otherwise indicated.

 

 

 

 

Egg as sampling unit Nest as sampling unit
hatch- 2 test
n ability statistica P-valueb n median statisticc P--valueb
Year
1996 76 97.4 0.73 0.466 6 100.0 64 >>0.100
1997 220 95.5 17 100.0
Site
HNF 245 95.1 1.62 0.105 19 100.0 56 >0.100
PRCSF 51 100.0 4 100.0
Area
open 212 98.1 3.00 0.003 16 100.0 85 >>0.100
closed 84 90.5 7 100.0
Nesting attempt
first 296 95.9 3.16 <0.002 23 100.0 35 0.020
second 36 83.3 5 87.5
Hen age
adult 158 97.5 1.42 0.156 12 100.0 0.84d 0.401
yearling 13 8 94.2 1 1 100.0

 

a Test for binomial proportions.

b Significance based on P < 0.004 (see Methods for Bonferroni adjustment).
° Wilcoxon rank sum T.

d A 2 statistic was used because both n, > 10.

48

removed as an outlier, the difference in hatchability between first and second nests would
increase. Egg hatchability was similar between years, study sites, and yearling and adult
hens.

Each of the 40 nests in this study was under observation for 2 to 28 days. The
median was 21 days, and the total was 753 nest-days for the 40 nests. Twenty-eight nests
were successful, 9 were destroyed, and 3 were abandoned when the hen was killed during
the egg-laying or incubation periods. The success rate of first nests was 47.8% (Table
11). This was lower than the 80.3% success rate of second nests only because it took
longer to lay the larger clutch of first nests. The 1.2% difference in daily survival rate
between first and second nests was not statistically significant (P = 0.184). However,
first nests surviving to hatch were at risk an average of 40.1 days, and second nests were
at risk for only 32.6 days. For all other comparisons of nest survival parameters, second
nests were included in the summation of the number of nest-days and the number of nests
that failed (see Mayfield 1961). However, only the mean time from initiation to
completion (hatching) of first nests was used to calculate nest survival rates for the entire
nesting period. Nest success rates and number of days at risk were similar between years.

study sites, open and closed areas, and yearling and adult hens (Table 1 1).

Chick Survival

In 1996, 26 transmitters--13 implants and 13 extemals--were placed on chicks
from 8 different broods. Radio-marked chicks were eventually divided among 9 broods
because of brood mixing, but the number of marked chicks per brood remained between 1

and 6. Eleven of the chicks marked in 1996 were at the PRCSF site, and 6 of them

49

Table 11. Mayfield nest survival rates of ruffed grouse in northern Michigan in 1996 and
1997.

 

Period
survival

Daily

Failed Observed survival Test

 

n nests nest-days (%) statistica P-valueb (%)c

Year

1996 12 4 226 98.23 0.24 0.810 48.84

1997 28 8 527 98.48 54.08
Site

HNF 27 7 523 98.66 0.77 0.444 58.19

PRCSF 13 5 230 97.83 41.46
Area

open 23 6 448 98.66 0.65 0.516 58.19

closed 17 6 305 98.03 45.00
Nesting attempt

first 34 11 604 98.18 1.33 0.184 47.83

second 6 1 149 99.33 80.296
Hen age°

adult 19 4 367 98.91 0.92 0.358 64.42

yearling 20 7 364 98.08 45.93

 

a Z test; ratio of the difference in daily survival rate to its standard error.

b Significance based on P < 0.004 (see Methods for Bonferroni adjustment).

° Nest survival for the entire nesting period based on a mean completion time (from
nest initiation to hatching) of 40. 1 3 days for first nests.

d Based on a mean completion time of 32.60 days for second nests.

° One hen was of unknown age.

50

were from a second nesting attempt. In 1997, 50 transmitters were placed on chicks from
12 different broods, with 1 to 6 marked chicks per brood. These transmitters were all of

the external type and were attached to chicks only at the HNF site.
At the time of capture chicks were 5 to 10 days old (Tc = 6.4 days) and weighed

16.0 to 43.0 g (1.: = 23.1 g). It was not possible to estimate chick survival from hatching
to the time of transmitter attachment in either year because there were still too many
chicks in the broods at the time of capture to be counted accurately.

Chicks that died within 5 days of transmitter attachment were not included in the
calculation of survival rates because their deaths were presumed to be related to the stress
of capture and handling. Four chicks were not included in survival calculations in 1996
because they died within 3 days of transmitter attachment. The survival rate from 14
June through 7 September 1996, was 31.1% (Figure 11). At the end of that period 6
chicks were still alive, and 2 were censored (Table 12). Ten of the 14 chick mortalities
occurred in the first half of the predispersal period.

Chicks with external transmitters had a higher survival rate than those with
implants, 42% versus 13% (Figure 12). This result, however, is not considered
significant (log rank test, P = 0.5). One implanted transmitter and 2 external ones
remained attached and functional into October 1996.

Only 2 marked chicks were excluded from the 1997 sample for survival
calculations because they died within 5 days of transmitter attachment. The trend toward
higher chick mortality early in the summer is more evident in 1997 than it was in 1996

(Figure 11). Only 1 chick died after 25 July in 1997. Chick survival from 9 June to 7

51

 

 

 

 

 

'3
.2
5 -------- -.
‘0 1
L — n
0.2 1
0+____vfi_ __ _ _
lO-Jun 2-Jul 24-Jul 1 S-Aug 6-Sep

Figure 11. Survival of ruffed grouse chicks in northern Michigan. Survival rate to
7 September was 31.1% in 1996 and 32.5% in 1997. The 2 curves are statistically
similar (log rank test, P = 0.75).

52

Table 12. Ending status and sources of mortality of ruffed grouse
chicks in northern Michigan during the summers of 1996 and 1997.

 

 

14 June-7 Sept, 9 June-7 Sept.,
1996 1997
Alive 6 8
Censored 2 9a
Dead 14 31
avian predation 4 (29%) 16 (52%)
mammalian predation 2 (14%) 4 (13%)
exposure 0 (0%) 1 (3%)
no diagnosis 8 (57%) 10 (32%)
Not includedb 4 2
Number of transmitters
placed in use 26 50

 

a F our of the censorings in 1997 occurred after 2 September.
b Chicks that died within 5 days of transmitter attachment. Mortality
presumed to be related to capture stress, so the chicks were not included in

survival calculations.

Survival

53

 

 

 

 

 

 

 

1.0
0.8 —
0°6J \ Implants
0.4 J -----------------------
’ Extemals
0.2 ~
0.0 4: _. 3 . __
14-Jun 4-Jul 24-Jul 1 3 -Aug 2-Sep
Date

Figure 12. Survival of ruffed grouse chicks with different methods of transmitter
attachment in northern Michigan in 1996. Each curve represents 11 chicks. Survival
rate to 7 September was 41.7% for chicks with external transmitters and 13.3% for
chicks with implants. The 2 curves are statistically similar (log rank test, P = 0.50).

54

September 1997, was 32.5%. At the end of that period 8 chicks were still alive, and 9
were censored (Table 12). Four of the censorings occurred during the first week of
September, which is when the transmitter batteries were expected to begin failing and the
fall dispersal period begins.

The cause of death was determined for fewer than half of the mortalities in 1996
(Table 12). Twice as many deaths were due to avian predators than mammalian
predators. Sixteen of the 31 mortalities in 1997 were known to have been caused by
avian predators, and 4 were due to mammalian predators. No source of mortality (“no
diagnosis” in Table 12) could be determined for many of the chicks in both years because
there were no remains to collect except a transmitter with no distinguishing holes, dents,
or scratch marks that may be left by a predator.

On 2 occasions in 1996 and 3 in 1997, 2 marked chicks from the same brood died
on the same day. Their remains were located 10-150 m apart, and in 2 of the cases it was
determined that both chicks died from the same source, avian predators. These results
indicate that the survival times were probably not independent within these pairs of
chicks. Although this violates an assumption of the Kaplan-Meier procedure, it affects
only the variance of the survival estimates, not the value of the estimates themselves.

Five marked chicks were involved in brood mixing before mid-August during the
study. Three marked chicks in 1996 left their original broods within 2 days of capture.
One of these was located back with its original brood 2 months later, but only for a day.

The 2 marked chicks that mixed with other broods in 1997 left their original broods after

55

37 and 58 days, respectively. One of these‘also returned to its original brood for a day
approximately 1 month after it had left.

Two radio-collared hens with broods containing marked chicks died during the
study. One was killed by an avian predator on 23 August 1997. Her 2 marked chicks
remained together for at least 4 days, and both survived until at least 3 September when
they were censored, probably because of transmitter battery failure. The other hen was
killed on 13 July 1997, when her chicks were 38-39 days old. She had 3 marked chicks,
and at least 7 others flushed with them when the brood was approached to collect the
hen’s remains. One of the marked chicks remained with its marked brood mates for 4
days and was killed by an avian predator on 25 July. It is uncertain whether the chick
was alone during its last week. The other 2 marked chicks remained together for 5 days.
One of them was with at least 1 other unmarked chick for up to another week. It was
censored on 23 August. The third marked chick was flushed alone on 25 July. On 25
August it was located with a marked chick from the other brood whose hen was killed.

The next day it was censored.

Population Modeling

Grouse chick production from first and second nests were estimated separately
because of the significant differences between first and second nests in survival rates
during the entire nesting period, clutch size, and egg hatchability. For every 100 hens
that begin nesting, the first nest survival rate indicates that approximately 48 will have a

successful first nest (Table 13). Hatching a mean of 12.2 chicks, those 48 hens will

56

Table 13. Relative ruffed grouse chick production for every 100 females that survived to
begin nesting in northern Michigan in 1996 and 1997.

 

 

First Second
nests nests Sum
Number of hens
attempting to nest 100.0 24.1 100.08
Number of hens
with a successful nestb 47.8 19.4 67.2
Initial brood sizec 12.2 6.1
Total number of hatchlinng 583.2 118.3 701.5
Number of chicks
surviving to dispersalc 186.6 37.9 224.5

 

3 Although approximately 124 nests are attempted, hens attempting a second nest are also
represented in the number of hens that attempted a first nest, so the total number of
individuals is still 100 hens.

b Product of the number of hens attempting a nest and the nest survival rate.

c Product of clutch size and egg hatchability.

d Product of the number of hens with a successful nest and the initial brood size.

c Product of the total number of hatchlings and the predispersal survival rate (~0.32).

57

produce 583 hatchlings. Initial brood size is the product of clutch size and egg
hatchability. Of the 52 hens whose first nest was unsuccessful at least 46% (6 of 13 hens
in this study), or 24, will be expected to attempt a second nest. This proportion may be
slightly higher because up to 4 of the hens in this study that did not appear to attempt a
second nest may have but abandoned it or had it destroyed before it was found. One-
hundred-eighteen chicks will be produced by the 19.4 successful (the product of the
number of hens attempting a nest and the nest survival rate) second nests, which hatch an
average of approximately 6.1 chicks each. An estimated 32% of the 702 hatchlings from
both first and second nests will survive to disperse. This results in approximately 225
juvenile grouse recruited into the fall population in early September for each 100 hens
that begin nesting. Given that some hens that begin nesting do not survive until fall and
assuming a juvenile sex ratio of 1:1 at dispersal, there would be approximately 200
female grouse in the early fall population.

Adult female grouse at the HNF and PRCSF study sites had fall-to-spring survival
rates of 0.61, 0.32, and 0.38 in 1994-95, 1995-96, and 1996-97, respectively. Juvenile
females had fall-to-spring survival rates of 0.53, 0.17, and 0.47 during the same years,
respectively. All females combined had fall-to-spring survival rates 2 0.45 during 2 of
the 3 years. Supporting material for the results of fall-to-spring survival are provided in
Appendix A.

Given the fall recruitment estimate from this study, the female segment of the
grouse population would need to have at least a 50% survival rate during the fall-t0-

spring period to sustain a steady grouse population. Female survival rates do reach that

58

level, although not consistently. The mean fall-to-spring survival estimate for females
from 1994 to 1997 was 0.42. At this level of survival recruitment into the fall population
would need to be at least 2.38 (instead of the observed 2.25) juveniles per spring hen to

sustain a steady grouse population.

DISCUSSION

Nest Sites

Within areas of suitable nesting habitat it appears that individual grouse hens
probably select nest sites nearly at random. Suitable nesting habitat can be described
only in general terms. Nearly all dominant overstory vegetation types are used. Some
researchers have found a strong preference for hardwoods--less than 5% of nests in
studies by Bump et a1. (1947:127-128) and Maxson (1978a) were located in conifer cover
types--but more than a third of the nests in this study were located in conifer stands.

The age of a forest stand also appears to be less important than the actual cover it
provides. Gullion (1977) reported that aspen stands between 25 and 30 years old provide
preferred nesting habitat because stern densities are below 4900 stems/ha and the closed
canopy prevents the growth of dense understory vegetation, which supposedly aid the
incubating hen in detecting predators. By comparison, none of the 13 aspen stands that
contained nests during the current study were 25-30 years old. Nine were younger, and 4
were older. Bump et a1. (1947: 127-128) reported that half of the nests in their 13-year

study were in “second growth” forests, and the other half were split nearly equally

59

60

between “young” and “mature” forests. The hens in my study also nested in forest stands
of nearly all seral stages.

Although stem density results from a study of nest sites in an oak/hickory forest
(Thompson et al. 1987) agree with Gullion’s (1977) prediction, fewer than half of the
nests sites in this study were in areas of <4900 stems/ha. This is probably due to the
definition of a stem that was used. The density of live woody stems >1 m tall is usually
much higher than the density of larger (for example >2-3 cm in diameter) erect woody
stems in the same area. Stem density measurements that include only the relatively large
stems are better descriptors of the quality of grouse nesting habitat because they indicate
the degree of forest thinning to which Gullion (1977) was referring. On the other hand,
the inclusion of the numerous, relatively small stems in determining stem density, as was
done in this study using a definition by Cade and Sousa (1985), seems to provide only a
redundant measure of understory cover.

No previous studies quantifying the amount of cover around ruffed grouse nest
sites have been found in the literature, and only Bump et a1. (1947:128) have given a
qualitative description. They found 40% of their nests in areas with “sparse
undergrowth,” 46% in areas with “medium undergrowth,” and 13% in areas with “dense
undergrowth.” The apparent nest success rate in their study was not affected by the
density of undergrowth. Maxson (1978b), however, did find a higher apparent nest
success rate in mixed hardwoods, where a thick covering of ferns emerged during the

incubation period, than in oak stands where it did not. The amount of cover, quantified

61

by several visual obstruction methods, did not appear to affect nest survival in the current
study. Bracken ferns (Pteridium aquilinum aquilinum) were not present when grouse
hens selected their nesting site, but they did provide much of the horizontal cover and
ground cover at most of the nest sites subsequent to the nesting season and presumably
during the later stages of incubation.

Ruffed grouse hens do prefer to position their nest against a solid object. Most
nests are at the base of trees, but other large portions of dead or dying trees that are on the
ground are utilized also. Although all nests in this study were positioned against a large
object, it does not appear that objects are necessary because several nests found by Bump
et al. (1947: 130) and Maxson (1978a) were not associated with any kind of object. For
those nests against trees, the size of the tree does not appear to be important. Maxson
(19780) reported that nest trees in his study were 5-29 cm in diameter. Nest trees in this
study were 1-35 cm in diameter. Also, at the PRCSF renesting hens selected trees that
averaged 15 cm larger in diameter than trees near first nests (Table 6). No meaningful
explanation can be found for this result. One may not be necessary considering that the
comparison is based on a small sample of only 4 first nests and 4 second nests, and no
such difference was found at the HNF site. There is no strong evidence in this study to
suggest that groups of grouse hens have preferences with respect to nest tree size.

This study found that there were more first nests on the south and east sides of the
object against which the nests were positioned than there were on the north and west
sides (Figure 3). More than half of the nests were on flat ground, but of the ones

positioned on a slope there was a slightly higher proportion facing south-east than any

62

other direction, and none of the slopes were facing north-west (Figures 6-8). Maxson
(1978a) found a slight preference for the south and south-west side of nesting objects and
slope aspect. Thompson et al. (1987) reported finding 12 of 13 grouse nests on south- or
west-facing slopes. Considered together, these results suggest that ruffed grouse hens
may have a weak preference for at least some southerly exposure of their nests. The mild
significance of this suggestion is minimized by the fact that all 4 cardinal directions were
selected in abundance in this study and others (Bump et al. 1947: 130, Maxson 1978a).
The final attempt in this study to describe grouse nesting sites was to quantify the
distance to other objects of possible importance to grouse hens, namely, the nearest
conifer tree, open area, and mature aspen tree. Conifer trees have been considered
detrimental to the quality of fall-to-spring habitat for ruffed grouse (Gullion 1977, Cade
and Sousa 1985). Hammill and Moran (1986), however, assert that conifer cover can be a
positive attribute of the habitat if both cover and long-range visibility are provided in the
stand. No speculation on the advantages or disadvantages of conifer trees in grouse
nesting habitat has been found in the literature. The results of this study agree with those
reported by Bump et al. (1947:132) (Table 6). Although approximately half of the nests
in each of the 2 studies were within 6 m of the nearest conifer tree, 21% of the nests in
the earlier study were >150 m from the nearest conifer tree, and nests in the current study
were up to 285 m from the nearest conifer tree. The distance to the nearest conifer tree
does not appear to negatively impact nesting success, and Bump et a1. (1947:132) explain
that, conversely, conifers do not seem to be a necessary element of the nesting habitat,

either.

63

The proximity of grouse nests to a forest opening is thought to be related to brood
habitat preferences rather than any significant benefit for the hen during the nesting
period. The distances to the nearest opening determined in this study are remarkably
similar to the results from 2 other studies (Table 6). Nearly 50% of all nests were within
10 m of an opening (Maxson 1978a), and 75% were within 30 m (Bump et al. 1947:132-
134). As expected, none of these studies revealed any effect of distance to the nearest
opening on nest survival.

The buds of mature aspen trees are known to be an important food resource for
ruffed grouse throughout the winter. Schladweiler (1968) found that grouse hens
continue to rely almost solely upon mature aspen trees (12-23 cm dbh) for food during
the nesting period, not for the buds but for the emerging leaves. Therefore, it may be
expected that the proximity to mature aspen trees would be important in the selection of a
nesting site. However, the nesting hens in a study by Maxson (1978b) rarely fed on the
nearest aspen trees. The nearest aspen trees were within 80 m (median = 29 m), but
incubating hens traveled up to 185 m (median = 75 m) to the aspen trees in which they
fed. The 2 hens Schladweiler (1968) observed utilized aspen trees up to 90 m away from
their nest. It appears that as long as there are aspen feeding sites within some threshold
range of probably not less than 100 m, the distance of the nearest mature aspen tree is of
little importance. The distances to the nearest mature aspen tree in my study are similar
to those reported by others, so the statistical differences I found [1 second nest at the

HNF site and the successful nests at the PRC SF site were much farther from the nearest

64

mature aspen tree than first nests and unsuccessful nests at the respective study sites

(Table 6)] are not likely to be ecologically significant.

Nesting Parameters

Ruffed grouse nest initiation and hatching dates are thought to be highly
dependent on latitude, with the nesting season beginning earlier in the more southern
portions of its range. Fisher (1939), working in 3 areas of Michigan within 100 km of the
HNF and PRCSF study sites, found the mean hatching date for all but 1 nest to be 9 June.
The excluded nest hatched on 8 July. These dates match the median first nest hatching
date of 10 June and the last second nest hatching date of 3 July in this study (Figure 10,
Table 8). At approximately the same latitude in Minnesota hatching dates averaged 4
June and 8 June in 2 different years (Maxson 1978a). In latitudes just south of the HNF
and PRCSF study sites--the state of New York, most of southern Ontario, and central
Wisconsin--hatching peaked near 1 June (Bump et al. 1947:284, Cringan 1970, Kubisiak
1978). Still further south--southemmost Ontario and northeastern Iowa--hatching peaked
during the last week in May (Cringan 1970, Porath and Vohs 1972). Porath and Vohs
(1972) reported a peak in the hatching of second nests 3 weeks after the peak for first
nests. The difference between the median hatching dates of first and second nests in the
current study was exactly 21 days, which suggests that the timing of second nests relative
to first nests may be consistent regardless of latitude.

Although it is uncertain exactly why it appears that some hens whose first nest is
destroyed attempt a second nest and some do not, the date of first nest destruction surely

is one factor. If a hen’s first nest is destroyed in early May when it contains only a few

65

eggs, it is likely she would attempt a second nest. This is because the risk and metabolic
costs of both nesting attempts combined is not much higher than for 1 complete first nest.
Also, the possible benefit of producing chicks is much higher than producing no chicks if
she were to not attempt a second nest, especially considering that ruffed grouse hens
rarely survive through more than 2 breeding seasons. If, on the other hand, a hen’s first
nest were destroyed in early June, she would not be expected to renest because the chicks
resulting from her second nesting attempt probably would not have sufficient time to
mature before winter, and her additional reproductive effort would be wasted. For hens
whose first nest is destroyed in mid- to late May, however, the probability that they
would attempt a second nest must depend on other factors.

The stage of the nesting sequence when the first nest is destroyed may be one
such factor. It has been considered unlikely that grouse hens would attempt a second nest
if they had begun incubation of their first nest before it was destroyed. In a study by
Maxson (1978a) none of the 6 hens whose first nest was destroyed during incubation
renested. Also, the only positively documented occurrence of a grouse’s second nesting
attempt was of a hen whose first nest was destroyed before incubation began (Barrett
1970). The current study, however, has documented the nesting sequence of 4 ruffed
grouse hens throughout their first and second nesting attempts in the same year. Two of
the hens were at least 9 days into incubation before their first nest was destroyed. Also, 1
hen did not attempt a second nest even though she had not yet begun incubation of her

first nest when it was destroyed. Therefore, the stage of the nesting sequence may not be

as important as previously thought.

 

66

The data in this study suggest that the age of the hen may influence whether or not
a second nest is attempted. Whereas 2 yearling hens renested and 3 did not, all 4 of the
adult hens that had the opportunity to renest did. These data are few, however, and do not
warrant any strong conclusion. No other reference to the effect of hen age on likelihood
of attempting a second nest was found in the literature.

The remaining discussion in this section on nesting parameters will deal with the
strictly quantitative variables that influence nesting productivity. Clutch size, nest
survival, and egg hatchability, along with the proportion of hens that attempt first and
second nests, determine the maximum possible increase in the grouse population each
year.

The mean clutch size of first nests in this study was 12.7 eggs (Table 9). It is
higher than the means of 11.5 and 11.9 eggs in “early nests” found in other studies
(Bump et al. 1947:361, Cringan 1970) and the means of 10.6-12.5 eggs reported by those
who did not distinguish between first and second nests (Fallis and Hope 1950, Fisher
1939, Leopold 19332362, Maxson 1978a, Rusch and Keith 1971). The mean clutch size
of second nests in this study was 7.3 eggs. It is lower than the means of 7.5 and 8.5 eggs
in “late nests” reported by Bump et al. (19472361) and Cringan (1970). The differences
between the results for clutch size from this study and others probably is due to the lack
of or imprecise classification of first and second nests in earlier studies.

Bump et al. (1947:359-360) suggested that yearling hens may produce smaller
clutches than older hens. This conclusion was based on captive grouse and 1 wild hen

that was observed with clutches of 10, 13, and 12 eggs when she was 1, 2, and 5 years

67

old, respectively. Maxson (1978a), however, reported that there was no difference in
average clutch size between adults and yearlings. Mean clutch sizes in this study also
were not significantly different by hen age, but the mean for yearlings was slightly
smaller than for adults for both first and second nests (Table 9). An inspection of nesting
records for individual grouse hens lends more support to the conclusion above. Four hens
had their full first nest clutch size observed for at least 2 years. In 3 cases the first year of
observation was 1995, so 3 years of data were possible. Hen #140 laid 12 eggs as a
yearling and 13 eggs each of the next 2 years. Hen #143 also laid 12 eggs as a yearling
and 13 eggs the next year. The age of hen #173 was not known when she was first
captured, and she laid clutches of 11, 14 and 12 eggs in 3 successive years. Hen #6024
was at least 2 and 3 years old when she laid clutches of 12 eggs each. It appears that
perhaps the variability in clutch size among hens prevents the detection of a difference in
clutch size according to hen age that is apparent within individual hens.

Nest success rates for ruffed grouse have been reported only as the percentage of
nests found that hatched chicks, which ranged from 59% to 86% (Bump et al. 1947:312,
Maxson 197 8a, Rusch and Keith 1971). This apparent nest success rate is much higher
than the actual success rate because successful nests are more likely to be located by
researchers. Since most nests are not located until after incubation begins, even with
radio-marked hens, one cannot account for the significant but unknown number of nests
that are destroyed during the egg-laying period. That is why the Mayfield method
(Mayfield 1961) was used to calculate actual nest survival rates for this study (Table 11).

Although the survival rate of second nests (80.3%) falls within the range of nest success

68

rates previously reported, the actual nest success rate in the entire population (first and
second nests combined) is still below that range.

Reported egg hatchability rates in successful nests range from 90% to 97% (Bump
et al. 1947:365, Cringan 1970, Fallis and Hope 1950, Fisher 1939, Rusch and Keith
1971). In the 1 study that attempted to distinguish between first and second nests egg
hatchability was approximately 2% lower in second nests (Bump et al. 1947:365). This is
comparable to the results from this study (Table 10), although egg hatchability in second
nests was 12.6% below the hatchability in first nests. Bump et al. (1947:366-367) found
that egg infertility rates nearly doubled and embryo mortality rates almost tripled in
second nests. Egg infertility would be expected to increase if hens did not copulate again
between laying their first and second clutches. The reasons for higher embryo mortality

in second nests, however, remain unclear.

Chick Survival

Previous to this study, miniature radio transmitters had not been attached to ruffed
grouse chicks. However, implanted transmitters similar to those used in this study were
found to not significantly affect the growth or behavior of ring-necked pheasant chicks
(Ewing et al. 1994). Also, Bakken et al. (1996) found that although mallard ducklings
with externally attached miniature transmitters showed areas of increased surface
temperature, neither implanted nor external transmitters had a biologically significant
effect on thermoregulation.

Both attachment procedures used in the current study were deemed successful in

terms of transmitter retention and minimal impact on chick survival. Although neither

69

transmitter attachment procedure was believed to significantly reduce chick survival,
there was a preference for the external suturing technique for several reasons. It required
less time, equipment, and expertise than the implantation procedure. External attachment
also did not require the wetting of chicks, and it involved less chance of accidental trauma
to chicks during the procedure.

Chick survival estimates for the predispersal period in this study (~32%) are much
lower than those reported by others. The summer survival rate of chicks was estimated to
be 80% based on mean monthly brood sizes (Domey and Kabat 1960). Comparing
decreasing mean monthly brood sizes to the mean initial brood size at hatching yielded a
survival estimate of 51% for the first 12 weeks of life (Rusch and Keith 1971). Bump et
al. (19472315) reported chick survival rates of just under 40% for the period from
hatching to 31 August, but a description of their methods was lacking.

Chick mortality is highest during the first half of the predispersal period (Figure
11) (Bump et al. 19472316). Therefore, if chick survival is estimated from mean brood
sizes, the initial brood size estimated directly from an analysis of nesting success also
should be used. If not, the survival estimate is inflated because much chick mortality
occurs before many of the first brood observations are obtained. Due to this and the other
disadvantages of using brood flush counts--variable sighting conditions, chronic
underestimation of brood size, brood intermixing, and total brood loss--direct measures of
chick survival should be favored.

Chick survival estimates in this study also do not include mortality that occurred

during the first week after hatching. Brood size counts at the time of chick capture and

70

transmitter attachment were attempted to account for mortality that occurred during the
first week. These brood size estimates should be considered highly unreliable because of
the large number of chicks and the extremely short amount of time they are able to be
observed before hiding when flushed. Another possible solution is to attach transmitters
to grouse chicks closer to the time of hatching. Smaller transmitters than the ones used in
this study are available, but the battery life is significantly reduced. However, accurate
estimation of chick survival is most important early in the predispersal period when there
are the most chicks and chick mortality is highest.

It is difficult to determine the causes of chick mortality. Visible signs of a
predator at the kill site are not as apparent during the summer as they are at other times of
the year, such as when there are tracks or impressions in the snow in winter. Also, the
abundance of feathers and other remains from the mortality of mature grouse that aid in
the determination of the cause are usually not present after a chick mortality. Finally, the
few remains that may be left by a predator (or the entire carcass of a chick dying from
exposure) are quickly consumed by insects and other small scavengers that are most
active during summer. Despite these problems it appears that avian predators are the
most significant source of predispersal mortality (Table 12). Mammalian predators
caused the second highest number of mortalities. Exposure and disease probably cause

few chick mortalities.

 

71

Population Modeling

The discrepancy between summer production of grouse chicks/juveniles and fall-
to-spring survival of females is small but remains significant because the grouse
population was believed to be increasing, not just remaining steady, during the years
when both estimates were made. Further analysis of the fall-to-spring data are necessary
and will help in developing a more comprehensive and consistent year-round model.
Future study of the proportion of hens that attempt second nests and a more refined
estimate of chick survival, including an evaluation of transmitter retention rates, also will

improve the model.

MANAGEMENT IMPLICATIONS

Ruffed grouse populations are typically managed through habitat management
and hunting regulations. Fall grouse mortality due to hunting has been shown to be
largely compensatory to other sources and has little direct effect on grouse recruitment
(Fischer and Keith 1974; Gormley 1996; S. R. Winterstein, Mich. State Univ., unpubl.
data). Grouse habitat, however, could be modified to improve recruitment.

If increasing grouse recruitment were a management objective, no forest harvest
should occur during the nesting period because many grouse nests are located in mature,
potentially harvestable stands. In addition, grouse nest near forest openings, which often
consist of logging trails, and the increased human disturbance along the trails that
accompanies forest harvest may reduce nest success and egg hatchability. Maximum
nesting productivity would require that mature aspen trees, the preferred food source for
incubating hens, be located within approximately 200 m of potential nesting areas. Brood
habitat also could be improved to increase chick survival, but examination of brood
habitat use and preference was beyond the scope of this study.

Predator exclusion should not be a goal of management from an ecosystem

perspective. However, the control of mammalian predator populations within the limits

72

73

of current hunting and trapping regulations almost certainly would increase the rates of
nest success and chick survival.

The most significant implications for ruffed grouse management from this study
are related to population modeling rather than field-oriented management applications.
There is a search for the factors that limit the rebound of grouse populations from the low
points in their lO-year cycle. So far, nearly all emphasis has been placed on fall-to-spring
survival rates. This study has shown that nesting success and chick survival rates are
substantially lower than previously estimated, suggesting that they may be limiting and
deserve more consideration than they have been given thus far. Our understanding of
annual ruffed grouse population dynamics will not be complete until the discrepancies
between estimates of juvenile recruitment and age-and sex-specific fall-to-spring survival

rates are resolved.

APPENDICES

APPENDIX A

APPENDIX A

FALL-TO-SPRING SURVIVAL

Fall-to-spring survival rates were determined for ruffed grouse at the HN F and
PRCSF study sites from 1993 to 1998. As mentioned in the Methods section above, a
complete discussion of fall trapping techniques were given by Clark (1996) and Gormley
(1996). They also described the methods for year-round radio telemetry and fall-to-
spring survival determination. A brief summary of the unpublished preliminary data that
are relevant to the incorporation of nesting production and chick survival into a year-
round population model is given here in Appendix A.

Comparisons of fall-to-spring survival rates were made between areas open and
closed to hunting and between study sites. This was done to test the appropriateness of
combining those samples of grouse to increase the sample size used in determining sex-
and age-specific survival rates. F all-to-spring survival rates were similar in areas open
and closed to hunting at both study sites in the 3 years subsequent to 1993-94 (Table A1).
Survival curves for those 3 years appeared to be more similar between study sites within
the same year (Figures Al-A3) than among years within the same study site (Figures A4-
A5). Formal testing revealed that the survival curves within each year were sufficiently
similar between study sites for the samples to be combined (Table A2). Sex- and age-
specific survival rates were calculated for each of the 3 years in which all the grouse in
the study presumably came from the same underlying population (Table A3). The
beginning and ending dates of the fall-to-spring period used in this analysis coincide with
the end of the predispersal period (7 September) and the median date of first nest

initiation (1 May), respectively.

74

Table A1. Log rank comparison of Kaplan-Meier survival functions for the period of 5
August to 15 May between areas open and closed to grouse hunting in northern Michigan

in 1993-1997.

75

APPENDIX A

 

 

Open area Closed area
Site Year survival rate survival rate X2 P-value
HNF 1993-94 0.00 0.23 3 .792 ~0.05
1994-95 0.40 0.37 1.310 >0.20
1995-96 0.21 0.10 1.507 >0.20
1996-97 0.37 0.35 0.527 ~0.50
PRCSF 1993-94 0.19 0.63 6.380 <0.02
1994-95 0.33 0.37 0.089 >0.70
1995-96 0.25 0.11 1.052 ~0.30
1996-97 0.26 0.25 0.125 >0.70

76

APPENDIX A

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APPENDIX A

 

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81

APPENDIX A

Table A2. Log rank comparison of Kaplan-Meier survival functions for the period of 5
August to 15 May between study sites in northern Michigan in 1994-1997.

 

 

HNF PRCSF
Year survival rate survival rate X2 P—value
1994-95 0.38 0.36 0.788 >0.30
1995-96 0.16 0.17 2.043 >O.10
1996-97 0.36 0.24 3.682 >0.05

 

 

82

APPENDIX A

Table A3. Kaplan-Meier survival rates for the period of 7 September to 1 May by sex
and age of ruffed grouse in northern Michigan in 1994-1997.

 

 

 

 

 

1994-95 1995-96 1996-97
n Survival 11 Survival n Survival

Females

Adults 35 0.61 29 0.32 29 0.38

Juveniles 58 0.53 78 0.17 64 0.47

All8 97 0.56 1 13 0.25 97 0.45
Males

Adults 47 0.44 48 0.14 40 0.3 3

Juveniles 53 0.39 66 0.20 76 0.29

Alla 103 0.41 122 0.16 119 0.30

 

8 Includes grouse of known sex but unknown age.

 

APPENDIX B

APPENDIX B

ORIGINAL DATA

Table Bl. Original categorical data for ruffed grouse nest sites in northern Michigan in
1996 and 1997.

 

Nest Orientation
Date Hen Nesting Hen Vegetation Nest object from nest Slope

sampled number attempt agea Siteb typec object typed objectc aspectf

 

6/1 1/96 66 1 Y HO j.p. trees beech NE

6/1 1/96 72 1 uk I-IO oak logs uk S SW
6/1 5/96 140 l A HO r.p. tree ironw. S SE
6/1 1/96 143 1 A HO aspen tree maple S

6/1 1/96 146 1 A HO aspen tree j.p. N

6/12/96 1 73 1 A HO tree irch E

6/11/96 196 1 Y HO j.p. snag j.p. E

8/7/96 4752 1 A PC w.p. trees maple S

8/7/96 6124 2 A PC r.p. tree w.p. W

8/7/96 464] 1 A PO aspen tree b. fir SW SW
8/7/96 4641 2 A PO aspen tree b. fir N

8/7/96 6024 1 A PO low tree b. fir E E
6/20/97 2022 1 Y HC aspen tree aspen SE NE
6/13/97 2036 1 Y HC aspen branch uk E SW
6/13/97 2106 1 Y HC j.p. log j.p. SE
7/3/97 2106 2 Y HC oak/h. snag aspen NW SE
6/20/97 2120 1 Y HC oak/h. log uk S S
6/1 3/97 2204 1 Y HC aspen branch uk SW

6/13/97 2209 1 Y HC aspen tree maple NE E
6/20/97 2680 1 Y HC j.p./oak tree oak S

6/20/97 2685 1 Y HC oak/h. tree maple N NE

83

84

APPENDIX B

Table Bl (cont’d)

 

Nest Orientation
Date Hen Nesting Hen Vegetation Nest object from nest Slope
sampled number attempt agea Siteb typec object typed objectc aspectf

 

6/ 1 6/97 0 1 uk HO aspen tree aspen N ,—
6/1 1/97 57 1 A HO aspen log aspen W
6/16/97 140 1 A HO j.p. tree oak E
7/ 1/97 173 1 A HO trees aspen W
6/1 6/ 97 242 1 Y HO oak tree aspen E
6/1 1/97 245 1 Y HO j.p. snag aspen SW
6/16/97 268 1 Y HO aspen tree aspen W
6/16/97 303 1 A HO aspen snag aspen E SE
6/1 6/97 3 16 1 Y HO r.p. branch oak N
6/ 1 6/97 326 1 Y HO aspen tree aspen W
6/1 1/97 329 1 Y HO j.p. tree j.p. S N
6/1 1/97 339 1 Y HO oak/h. tree r.p. S
7/7/97 6063 2 Y PC grass tree w.p. W
7/7/97 6078 1 A PC log uk
7/7/97 6078 2 A PC stump uk NE
7/7/97 6371 1 A PC r.p. tree aspen SW
mm 6371 2 A PC 8. conif. stump uk N
7/7/97 4654 1 A PO maple tree maple NW SE 1
7/7/97 6024 1 A PO low snag cedar SE SE

 

a Y = yearling, A = adult, uk = unknown.

b HO = HNF open area, HC = HNF closed area, P0 = PRCSF open area, PC = PRCSF
closed area.

c j.p. = jack pine, r.p. = red pine, w.p. = white pine, low = lowland brush, h. = hickory, s.
conif. = swamp conifer, blank indicates nest was on private property.

d ironw. = ironwood, b. fir = balsam fir, j.p. = jack pine, r.p. = red pine, w.p. = white pine,
uk = unknown.

‘ N = north, NE = northeast, E = east, SE = southeast, S = south, SW = southwest, W =
west, NW = northwest, blank indicates nest was directly beneath the log or branch.

f Blank indicates nest was on level ground. Abbreviations are the same as for the
previous variable.

 

85

APPENDIX B

 

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APPENDIX B

Table B4. Original data for ruffed grouse chicks captured in northern Michigan in 1996.

 

 

Chick Age at Weight Date Source
num- capture at cap- Hen Study Radio Capture out of of
ber (days)a ture (g) number siteb typec date study Statusd mortalityc
1 5-6 20.0 6024 PO S 6/14/96 6/21/96 mortality no diag.
2 6 23.0 146 HO I 6/14/96 6/16/96 radio only no diag.
3 6 24.5 146 HO S 6/14/96 6/16/96 mortality mammal
4 5 17.0 143 HO I 6/15/96 6/29/96 radio only no diag.
5 5 18.0 143 HO I 6/15/96 7/16/96 censored
6 5 16.5 143 HO S 6/15/96 6/28/96 radio only no diag.
7 10 30.0 143 HO S 6/20/96 7/18/96 mortality mammal
8 7 20.5 140 HO I 6/20/96 6/23/96 mortality avian
9 7 21.0 140 HO S 6/20/96 9/18/96 mortality avian
10 10 42.5 173 HO I 6/20/96 9/1/96 mortality avian
11 10 43.0 173 HO S 6/20/96 6/21/96 mortality stress
12 uk 20.0 1 HO I 6/21/96 7/13/96 radio only no diag.
13 uk 21.5 1 HO I 6/21/96 7/9/96 radio only no diag.
l4 uk 22.0 1 HO S 6/21/96 9/1 8/96 censored
15 1 1 34.0 143 HO S 6/21/96 9/14/96 censored
16 uk 29.0 1 HO S 6/24/96 7/3/96 mortality avian
17 6-7 24.0 4752 PC I 6/25/96 10/9/96 censored
18 6-7 21.0 4752 PC I 6/25/96 7/8/96 mortality mammal
19 6-7 28.0 4752 PC S 6/25/96 7/15/96 mortality avian
20 6-7 27.0 4752 PC S 6/25/96 7/15/96 mortality avian
21 5 17.0 6124 PC I 6/27/96 8/25/96 radio only no diag.
22 5 17.0 6124 PC I 6/27/96 8/25/96 radio only no diag.
23 5 16.5 6124 PC S 6/27/96 10/2/96 censored
24 5 16.0 6124 PC S 6/27/96 10/9/96 censored
25 7 21 .5 6124 PC I 6/29/96 8/ l 2/ 96 censored
26 7 22.5 6124 PC 1 6/29/96 7/31/96 radio only no diag.

 

3 uk = unknown age because the chicks were from a nest that was not under observation.
b HO = HNF open area, P0 = PRCSF open area, PC = PRCSF closed area.

c S = sutured externally, I = implanted.

d radio only = only an unmarked transmitter was collected; presumed mortality.

° no diag. = no diagnosis, stress = exposure or stress due to capture.

APPENDIX B

Table B5. Original data for ruffed grouse chicks captured in northern Michigan in 1997.

 

 

Chick Age at Weight Date Source
num- capture at cap- Hen Study Radio Capture out of of
ber (days) ture (g) number siteII typeb date study Statusc mortalityd
27 5 18 .5 329 HO S 6/9/97 10/7/97 censored
28 5 18.5 329 HO S 6/9/97 6/14/97 mortality no diag.
29 5 19.0 329 HO S 6/9/97 6/26/97 mortality avian
30 5 19.0 329 HO S 6/9/97 9/10/97 censored
3 1 5-6 20.0 57 HO S 6/10/97 8/26/97 censored
32 5-6 19.5 57 HO S 6/10/97 7/25/97 mortality avian
33 7-8 23.0 57 HO S 6/12/97 8/23/97 censored
34 6 20.5 2209 HC S 6/13/97 6/21/97 mortality avian
35 6 19.5 2209 HC S 6/13/97 6/23/97 radio only no diag.
36 6 22.5 2209 HC S 6/13/97 6/21/97 radio only no diag.
3 7 6 1 9.5 2209 HC S 6/1 3/97 9/6/97 censored
38 6 20.5 2209 HC S 6/13/97 6/27/97 mortality avian
39 6 20.5 2209 HC S 6/13/97 6/27/97 mortality avian
40 8-9 22.5 316 HO S 6/15/97 9/21/97 censored
41 8-9 21.5 316 HO S 6/15/97 8/12/97 mortality no diag.
42 8-9 20.5 3 16 HO S 6/1 5/97 7/22/97 mortality avian
43 6 26.0 242 HO S 6/15/97 7/6/97 radio only no diag.
44 6 24.5 242 HO S 6/1 5/97 8/1 6/97 censored
45 6 23 .5 242 HO S 6/15/97 alive‘
46 6 26.5 242 HO S 6/1 5/97 7/3/97 mortality avian
47 6 21 .0 268 HO S 6/16/97 7/4/97 mortality mammal
48 6 21 .5 268 HO S 6/16/97 8/16/97 censored
49 6 21 .5 268 HO S 6/16/97 6/26/97 mortality stress
50 6 23 .0 268 HO S 6/16/97 7/1 1/97 mortality avian
5 l 6 21 .0 268 HO S 6/16/97 6/26/97 mortality mammal
52 6 23 .5 303 HO S 6/17/97 9/3/97 censored
53 6 23 .0 303 HO S 6/17/97 6/23/97 mortality avian
54 6 25.0 303 HO S 6/ 1 7/97 7/6/97 mortality avian
55 6 24.0 303 HO S 6/1 7/97 6/29/97 mortality avian
56 6-7 29.5 2680 HC S 6/17/97 9/26/97 censored
57 7 23 .5 2120 HC S 6/17/97 9/16/97 censored
58 7 24.5 2120 HC S 6/17/97 6/21/97 mortality avian
59 7 25 .0 2120 HC S 6/17/97 7/16/97 mortality mammal

 

 

Table B5 (cont’d)

91

APPENDIX B

 

 

 

Chick Age at Weight Date Source
num- capture at cap- Hen Study Radio Capture out of of
her (days) ture (g) number sitea typeb date study Statusc mortalityd
60 6 28.5 2022 HC S 6/17/97 9/6/97 censored

61 6 24.5 2022 HC S 6/17/97 6/24/97 radio only no diag.
62 6 26.0 2022 HC S 6/17/97 7/4/97 radio only no diag.
63 6 25.5 2022 HC S 6/17/97 7/1/97 mortality avian
64 6 19.0 140 HO S 6/18/97 7/23/97 radio only no diag. 1
65 6 18.5 140 HO S 6/18/97 7/2/97 mortality avian
66 6 20.0 140 HO S 6/18/97 6/23/97 radio only no diag.
67 6 1 7.0 140 HO S 6/18/97 9/14/97 censored

68 6 19.5 140 HO S 6/18/97 7/12/97 mortality avian
69 6 20.0 ' 140 HO S 6/18/97 9/14/97 censored

70 8 26.5 2120 HC S 6/18/97 6/21/97 mortality avian

71 7 29.5 2022 HC S 6/18/97 7/19/97 mortality avian
72 7 28.0 303 HO S 6/1 8/97 9/3/97 censored

73 7 29.5 303 HO S 6/18/97 7/23/97 censored

74 6 27.0 173 HO S 6/28/97 7/11/97 radio only no diag.
75 6 25.0 173 HO S 6/28/97 7/7/97 mortality avian
76 6 26.0 173 HO S 6/28/97 7/4/97 mortality mammal

 

8‘ HO = HNF open area, HC = HNF closed area.

b

S = sutured externally.

c radio only = only an unmarked transmitter was collected; presumed mortality.

d . . .
no diag. = no diagnoms, stress = exposure or stress due to capture.

° Chick #45 was recaptured by nightlighting on 25 August 1997, was fitted with a bib-
type transmitter, and was known to be alive as of 1 March 1998.

LITERATURE CITED

 

 

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