The Condor 107:87–96
q The Cooper Ornithological Society 2005
GENDER IDENTIFICATION AND GROWTH OF JUVENILE
LESSER PRAIRIE-CHICKENS
JAMES C. PITMAN1,4, CHRISTIAN A. HAGEN1, ROBERT J. ROBEL1, THOMAS M. LOUGHIN2
AND ROGER D. APPLEGATE3
1Division of Biology, Kansas State University, Manhattan, KS 66506
Department of Statistics, Kansas State University, Manhattan, KS 66506
3Survey and Research Office, Kansas Department of Wildlife and Parks, P.O. Box 1525, Emporia, KS 66801
2
Abstract. The ability to ascertain gender and age of juvenile grouse is essential for
determining gender-specific population age structure and studying timing of reproductive
events, respectively. We examined outer rectrix feathers from juvenile Lesser PrairieChickens (Tympanuchus pallidicinctus) captured at 30–40 and 50–60 days post-hatching.
Blood samples were collected from most chicks captured after 50 days post-hatching and
molecular analysis of blood cells was used to validate our field method for ascertaining
gender. Barring on the inner half of the outer rectrices was a poor method for identification
of the gender of juvenile Lesser Prairie-Chickens in Kansas as only 17 of 28 (61%) and
20 of 31 (65%) chicks were classified correctly at 30–40 and 50–60 days post-hatching,
respectively. The extent of barring on the outer half of the rectrix was a better method of
gender identification as 100% (15 of 15) and 90% (17 of 19) of juveniles were correctly
identified at 30–40 and 50–60 days post-hatching, respectively. Mean body characteristics
at hatching were measured for mass (15.5 g), foot length (20.1 mm), tarsometatarsus
length (18.2 mm), and flattened wing length (20.5 mm). Measurements from hatching to
320 days post-hatching for each body characteristic were used to fit standardized growth
curves. Logistic curves best described the development of each body characteristic except
wing length. The Gompertz equation more accurately described growth of Lesser PrairieChicken wings.
Key words: foot length, growth rate, Lesser Prairie-Chicken, mass, tarsometatarsus
length, Tympanuchus pallidicinctus, wing length.
Identificación del Sexo y Desarrollo de los Juveniles de Tympanuchus pallidicinctus
Resumen. La identificación del sexo y las edad de los urogallos juveniles es esencial
para determinar la estructura de edades para cada sexo en las poblacionesy para estudiar el
momento en que ocurren los eventos reproductivos, respectivamente. Para determinar el
sexo de individuos de la especie Tympanuchus pallidicinctus, examinamos las rectrices
externas de juveniles capturados entre 30–40 y 50–60 dı́as después de salir del cascarón.
También colectamos muestras de sangre de la mayorı́a de los pollos capturados después de
50 dı́as de haber eclosionado, e hicimos análisis moleculares de las células sanguı́neas para
verificar la validez de nuestro método de campo para determinar el sexo. La observación
del barreteado de la mitad interior de las timoneras externas no fue un método satisfactorio
para identificar el sexo en T. pallidicinctus en Kansas, pues sólo permitió clasificar correctamente 17 de 28 (61%) y 20 de 31 (65%) pollos de 30–40 y 50–60 dı́as de edad, respectivamente. El método consistente en examinar el grado y número de barras en la parte
exterior de las timoneras resultó ser mejor para determinar el sexo, ya que permitió clasificar
correctamente el 100% (15 de 15) y el 90% (17 de 19) de los juveniles de 30–40 y 50–60
dı́as de edad, respectivamente. Las caracterı́sticas corporales medias medidas al momento
de nacer fueron: masa (15.5 g), longitud de la pata (20.1 mm), longitud del tarsometatarso
(18.2 mm) y longitud del ala aplanada (20.5 mm). Con el objetivo de establecer curvas de
desarrollo estandardizadas para cada una de estas caracterı́sticas corporales, empleamos medidas tomadas el dı́a de eclosión y 320 dı́as más tarde. El desarrollo de todas las caracterı́sticas corporales, excepto la longitud del ala, fue descrito más adecuadamente por curvas
logı́sticas. La ecuación Gompertz describió con más exactitud el crecimiento de las alas.
Manuscript received 30 December 2003; accepted 11 October 2004.
Present address: Indiana Division of Fish and Wildlife, 4112 State Road 225 East, West Lafayette, IN 47906.
E-mail: jpitman@dnr.in.gov
4
[87]
88
JAMES C. PITMAN
ET AL.
INTRODUCTION
The distributions of most prairie grouse species
have been markedly reduced over the last 30
years, and declines in abundance have also been
documented (Silvy and Hagen 2004). The
Sharp-tailed Grouse (Tympanuchus phasianellus) still occupies most of its historical range
but population numbers in the southern and eastern portions of its range are declining (Connelly
et al. 1998). Greater Prairie-Chickens (Tympanuchus cupido pinnatus) have been extirpated
from four Canadian provinces and 9 of 20 states
that are believed to comprise their historical distribution (Svedarsky et al. 2000). Additionally,
one subspecies of Greater Prairie-Chicken has
been extirpated (T. c. cupido) and another (T. c.
attwatteri) is federally listed as endangered
(Storch 2001). The status of the Greater SageGrouse (Centrocercus urophasianus) is currently in review and Gunnison Sage-Grouse (C. minimus) is a candidate species for federal protection under the Endangered Species Act in the
United States (Schroeder et al. 2004). The Greater Sage-Grouse is a federally protected endangered species in Canada (Aldridge and Brigham
2003). Similarly, the Lesser Prairie-Chicken
(Tympanuchus pallidicinctus) has been listed as
a ‘‘warranted but precluded’’ threatened species
(United States Fish and Wildlife Service 2002)
as a result of long-term population declines and
.90% reduction in habitat (Taylor and Guthery
1980, Giesen 1998, Silvy and Hagen 2004).
Because most grouse populations are declining, it has become increasingly more important
to develop accurate non-invasive methods to
identify gender of juveniles. Ascertaining gender
of juvenile grouse is essential for determining
gender-specific age structures of populations.
Most grouse species are sexually dimorphic but
gender-specific differences are not easily observed in birds ,6 weeks of age. Gender of
birds can be ascertained by molecular analysis
of blood or feathers at any age (Griffiths 1998),
but this technique is costly and time consuming.
Davison (1957) suggested barring on the inner
half of the outer rectrices could be used to differentiate the gender of Lesser Prairie-Chickens
as early as 4–5 weeks post-hatching. Molecular
sexing techniques now allow us to assess the
accuracy of this technique.
Ascertaining the age of juvenile grouse allows
researchers to study body growth and develop-
ment, and timing of reproductive events (McCourt and Keppie 1975). Several grouse species
can be classified as juveniles or adults from
plumage characteristics. However, few methods
exist to estimate the age (days post-hatching) of
grouse chicks. Wing molt has been used to estimate the age of young grouse (Zwickel and
Lance 1966, Redfield and Zwickel 1976, Petersen and Braun 1980), but molt can be highly
variable among individual birds. Fitting standardized growth curves (Ricklefs 1968, 1973) to
grouse morphometrics is a reliable technique for
predicting the age of juvenile birds but this
method has only previously been used to describe age-specific changes in body mass for five
grouse species (Ricklefs 1968, 1973, McEwen
et al. 1969, Redfield and Zwickel 1976, Lindén
1981). Models describing the growth of other
body characteristics do not exist for any grouse
species and no information is available on agespecific growth of Lesser Prairie-Chickens (Giesen 1998).
This research was conducted to assess the accuracy of plumage characteristics (Davison
1957) in identifying juvenile Lesser PrairieChicken gender. Second, we examined if standardized growth curves (Ricklefs 1968, 1973)
including body mass, foot length, tarsometatarsus length, and wing length produce reliable estimates of age in juvenile Lesser Prairie-Chickens.
METHODS
Data were collected from birds captured between 2000 and 2002 south of the Arkansas River in Finney County, Kansas (378529N,
1008599W) on two areas each approximately
5000 ha in size. Sand sagebrush (Artemisia filifolia) was the most obvious vegetation component on each area and the primary grasses were
native bunch grasses typically associated with
Lesser Prairie-Chicken habitat in southwest
Kansas (Hulett et al. 1988). The invertebrate
components were diverse with short-horned
grasshopper (Acrididae) biomass constituting
.70% of all invertebrates collected in sweepnets
(Jamison et al. 2002).
We used long-handled nets and spotlights to
capture chicks at night by locating radio-tagged
females with broods. We measured body mass
of captured chicks to 0.1 g on an electronic scale
(Ohaus Corporation, Pine Brook, New Jersey).
Calipers were used to measure tarsometatarsus
DEVELOPMENT OF JUVENILE LESSER PRAIRIE-CHICKENS
length (2001–2002) and an aluminum wingchord ruler was used to measure foot length
(2001–2002) and wing-chord length (2002) to
the nearest 1 mm. Greatest length of the tarsometatarsus was measured from the posterior
proximal joint of the tibia and metatarsus to the
anterior distal joint at the base of the middle toe
(Pyle 1997). With the foot at a right angle to the
tarsometatarsus, foot length was measured by
placing the upright of the wing-chord ruler
against the posterior edge of the heel joint and
measuring to the end of the middle toe excluding
toenail. Wing length was measured from distal
end of the carpal joint to tip of the longest primary, wing pressed flat against ruler (Pyle
1997).
Chicks captured .30 days post-hatching were
equipped with an aluminum leg band provided
by Kansas Department of Wildlife and Parks
(KDWP). We used presence or absence of barring on the inner half of the outer rectrices (Fig.
1) to classify birds as female or male, respectively (Davison 1957). Beginning in 2001, we
collected alternating outer rectrix feathers from
chicks captured at 30–40 and 50–60 days posthatching for later examination. Beginning midway through the first field season, we took blood
samples from captured chicks older than 50 days
post-hatch and submitted them to Zoogen Incorporated (Davis, CA) for molecular analysis to
identify the gender of each bird (Griffiths 1998).
We used spring recaptures at leks during subsequent years to identify the gender of some
birds not classified by molecular analysis (n 5
4). Capture and handling procedures were approved by the Animal Care and Use Committee
at Kansas State University (ACUC Protocol
#2609).
STATISTICAL ANALYSES
We used a 1-tailed z-test (Agresti 1996) to examine if the probability of correctly identifying
rectrix feathers individually to gender differed
from random chance at 30–40 and 50–60 days
post-hatching. Fisher’s exact test (Agresti 1996)
was used to compare the accuracy of gender
identification between growth stages. Data are
presented as mean 6 SE and we used an a-value
of 0.05 for all statistical analyses.
We developed growth curves for four Lesser
Prairie-Chicken body characteristics (mass, foot
length, tarsometatarsus length, and wing length)
using SAS version 8.1 (SAS Institute 1999). Day
89
of hatch was designated as day 0 for all modeling procedures. Data from the four body characteristics were fitted using reparameterizations
of the two most commonly used growth equations (Ricklefs 1973):
Gompertz:
W 5 Ae2e
logistic:
W5
2K(t2I)
A
,
1 1 e 2K(t2I)
(1)
(2)
where W represents size at time t (days), A the
final size or asymptote, I the inflection point at
which 37% (Gompertz) and 50% (logistic) of
the asymptotic size is achieved, and K a constant
proportional to the overall growth rate (Ricklefs
1968, Zack and Mayoh 1982). Because K is not
directly comparable between the Gompertz and
logistic models, we used an alternative parameter, t10–90 which is the time interval for growth
from 10 to 90% of the asymptote (Ricklefs
1967). Because 10% of the estimated asymptote
for foot, tarsometatarus, and wing length was
less than the mean measurement at hatch, the
time interval for growth from 50 to 90% of the
asymptote (t50–90) was calculated for these morphological characters.
We used measurements collected from
known-age birds (regardless of gender) to fit
both models for the four body characteristics.
Data were pooled across all three years because
of small sample sizes. Parameters (K, I, and A)
were estimated by least squares using the Marquardt algorithm. Because these models were
developed primarily to predict the age of juvenile Lesser Prairie-Chickens, the model fit was
most closely examined for birds ,65 days posthatching. Model fit was often poor for this portion of the curve (measured from residual plots)
due to heterogeneous variance between birds of
different ages (morphometrics were more variable for older birds). Therefore, we placed greater weight on smaller observations during the
modeling process (Draper and Smith 1981) forcing the curve to more accurately describe growth
of younger birds. The model and weighting (if
necessary) combination that provided the best fit
(measured from residual plots) for birds ,65
days post-hatching was selected as the final
model. We developed gender-specific models
only for change in body mass because sufficient
data were not available for the other three morphometrics. We fixed asymptotic mass at mean
90
JAMES C. PITMAN
ET AL.
values of spring-caught yearling male and female Lesser Prairie-Chickens.
A bootstrap-resampling procedure (Manly
1998) was necessary to obtain 95% confidence
intervals for each estimated parameter because
models were created with non-independent observations (multiple measurements from broods
and individual birds). For each of the 5000 iterations, broods were resampled with replacement to match the total number of broods in the
original data set. The selected model was refit to
the resampled data set and all parameters re-estimated. Sampling distributions were developed
for each estimated parameter and 95% bootstrap
bias-corrected and accelerated (BCA) confidence intervals were taken from the resulting
distributions.
We used the Lesser Prairie-Chicken morphometrics measured in our study to develop a reference table with predicted ages for arbitrarily
selected measurements using the inverse of the
derived Gompertz
Age (days) 5 {2(1 K21)
3 log(2log[W A21])} 1 I
and logistic equations
Age (days) 5 2(1 K21)
3 log([A W21] 21) 1 I.
Ninety-five percent prediction intervals were
created at selected values within a range of masses (20–500 g), foot lengths (20–44 mm), tarsometatarsus lengths (18–50 mm), and wing
lengths (25–180 mm) based on 5000 bootstrapestimated curves.
RESULTS
GENDER IDENTIFICATION
Molecular analysis of gender for 31 chicks captured prior to 60 days post-hatching resulted in
19 males and 12 females. We classified 17 of 28
(61%) of these birds into the correct gender at
30–40 days post-hatch by the presence or absence of barring on the inner half of the outer
rectrices, a level of accuracy that did not differ
from random (z1 5 1.1, P 5 0.17). The absence
of barring on rectrices of females led to more
males (15 of 18, 83%) than females (2 of 10,
20%) being classified correctly. Accuracy of
gender identification at 50–60 days post-hatching was also not different from random (z1 5
1.6, P 5 0.08) as only 20 of 31 (65%) chicks
were correctly classified. Males at 50–60 days
old were classified correctly with a greater percentage (16 of 20, 84%) than females (4 of 12,
33%). Overall, identifying gender from barring
on the inner half of the outer rectrices was a
poor technique and accuracy did not improve
(x21 5 0.1, P 5 0.79) between 30–40 and 50–
60 days post-hatching.
We retrospectively examined 15 rectrices collected from 8 males and 7 females at 30–40
days post-hatching and all 15 were correctly
classified by the presence or absence of heavy
barring on the outer portion of the feather (Fig.
1). Gender was correctly identified using barring
on the outer portion of the feather for 17 of 19
(90%) chicks at 50–60 days post-hatching. Classification accuracy was similar between males (9
of 10, 90%) and females (8 of 9, 89%).
GROWTH
We collected measurements of body mass from
70 chicks in 24 broods, foot length from 61
chicks in 18 broods, tarsometatarus length from
61 chicks in 18 broods, and wing length from
20 chicks in 10 broods. We recorded mass measurements from birds ranging from hatching to
320 days post-hatching with .70% recorded
from birds younger than 60 days. For each of
the other three body characteristics, only one
measurement was recorded beyond 60 days
post-hatching (64 days post-hatching). Means
were calculated at 5- or 6-day intervals (depending on sample size) for 8 growth periods
prior to 60 days post-hatching (Table 1). No data
were collected between 16–24 and 46–54 days
post-hatching for any of the four morphometrics.
The logistic equation best-described gains in
Lesser Prairie-Chicken mass (Fig. 2A), and
change in foot length and tarsometatarsus length
(Fig. 2B, C) during the first 65 days post-hatching whereas wing growth was best-described
with the Gompertz equation (Fig. 2D). Change
in body mass occurred at a much slower rate
than growth of the foot, tarsometatarsus, or
wing, as reflected by number of days for growth
to reach 90% of the estimated asymptote (Table
2). The estimated asymptotes were either slightly less (mass, wing) or more (foot length, tarsometatarsus) than mean measurements recorded
from yearlings. The value t10–90 was calculated
only for mass because 10% of the asymptote
DEVELOPMENT OF JUVENILE LESSER PRAIRIE-CHICKENS
91
FIGURE 1. Feathers illustrating the absence of barring on the inner half of male and female Lesser PrairieChicken rectrices at 30–40 and 50–60 days post-hatching and more distinct barring on the outer half of female
rectrices.
was less than length at hatch for the other three
morphometrics.
Gender-specific models were fit to 13 masses
of 9 female chicks from 8 broods and 39 masses
of 22 male chicks from 13 broods (Fig. 3). Neither the logistic nor Gompertz equation provided
a good fit to Lesser Prairie-Chicken mass gains
when the asymptotes were fixed. The logistic
equation was selected as the best model because
residuals were smaller and resembled a more
random scatter. By fixing the asymptote at mean
yearling male (789 6 4 g, n 5 137) and female
(719 6 6 g, n 5 54) mass, time required for
mass gain to 90% of the asymptote was similar
between males and females (Table 2).
The inverse of the derived models provided
age estimates from measurements of each body
characteristic (Table 3). The mass model was capable of predicting juvenile age to within an interval of not more than 6 days (95% Prediction
TABLE 1. Measurements (mean 6 SE) of body mass, foot length, tarsometatarsus (tarsus) length, and wing
length for juvenile Lesser Prairie-Chickens from 0 to 60 days post-hatching in southwestern Kansas. Time
intervals of 5 or 6 days were used to summarize the data depending upon sample size.
Age (days
post-hatch)a
Hatch dayb
0–5
6–10
11–15
25–30
31–35
36–40
41–45
55–60
n
4
14
8
10
4
15
11
2
9
Mass (g)
n
Foot length
(mm)
n
6
6
6
6
6
6
6
6
6
8
19
12
10
3
7
7
2
9
20.1
20.5
24.4
24.9
38.7
42.4
44.3
44.5
44.9
6
6
6
6
6
6
6
6
6
8
19
12
10
3
7
7
2
9
15.5
17.3
26.0
39.4
123.0
187.4
236.2
238.5
406.8
0.5
0.8
0.4
0.7
13.1
14.7
10.8
21.5
7.8
a No data were collected from chicks between 16–24
b These data are for a subset of birds for which we
0.2
0.3
0.3
0.1
1.3
1.2
0.4
0.5
0.4
Tarsus length
(mm)
n
Wing length
(mm)
6
6
6
6
6
6
6
6
6
4
5
4
0
2
1
5
1
8
20.5 6
20.4 6
57.8 6
–
125.0 6
147.0
154.0 6
162.0
180.9 6
18.2
19.2
23.4
26.1
40.0
45.3
46.5
49.0
51.6
0.8
0.6
1.1
0.2
1.5
0.5
1.0
2.0
0.6
0.1
0.5
3.1
6.0
1.4
1.6
and 46–54 days post-hatching.
had morphometric measurements on the exact day of
hatching. These individuals are also included in the 0–5 age category.
92
JAMES C. PITMAN
ET AL.
FIGURE 3. Gender-specific growth curves describing change in body mass for juvenile Lesser PrairieChickens using the logistic equation with fixed asymptotes.
FIGURE 2. Relationship between morphological
characters and growth curves of Lesser Prairie-Chickens as described by the logistic (A, mass; B, foot
length; and C, tarsometatarsus length) and Gompertz
(D, wing length) equations.
Intervals) for birds ,500 g. Wing growth provided the same predictability for wings ,75
mm. Models derived from measures of foot
length and tarsometatarsus length had a much
lower level of predictability. The model describing change in foot length was capable of predicting age only within 14 days for feet ,34 mm
long (Table 3). From information on tarsometatarsus length, the model was capable of predict-
ing age within 14 days for tarsometatarsus
lengths ,38 mm (Table 3).
DISCUSSION
This study provides the first information on accurate gender identification, growth, and development of juvenile Lesser Prairie-Chickens. The
presence or absence of barring on the inner half
of the outer rectrices (Davison 1957) was a poor
method for ascertaining the gender of Lesser
Prairie-Chickens prior to 60 days post-hatching
in southwestern Kansas. Davison (1957) reported that at 4–5 weeks post-hatching, barring on
female rectrices was uniform across the vane on
both sides of the rachis, whereas males showed
TABLE 2. Parameter estimates and 95% bootstrap bias-corrected accelerated confidence intervals (CIL, CIU)
for equations describing growth of Lesser Prairie-Chickens in southwestern Kansas. Growth rate (K), inflection
point (I), and asymptote (A) were estimated from the logistic equation for all morphometrics except wing length
that was modeled with the Gompertz equation. Time (t) needed to grow from 10 to 90% of the asymptote is
presented for mass and 50 to 90% of the asymptote for foot, tarsometatarsus, and wing length. Dashes represent
variables not estimated during the modeling process.
K
Morphometric variable
Mass (g)
Male
Female
Foot length (mm)
Tarsometatarsus length (mm)
Wing length (mm)
Aa
I
Estimate
CIL
CIU
Estimate
CIL
CIU
Estimate
CIL
CIU
t
0.084
0.078
0.074
0.060
0.066
0.065
0.078
0.056
0.058
0.040
0.055
0.053
0.093
0.094
0.080
0.074
0.076
0.092
47
48
51
10
13
12
43
52
54
7
10
7
50
55
60
20
16
14
697
789
719
51
55
191
640
–
–
48
53
143
753
–
–
60
61
200
54
57
61
38
46
29
a All asymptotes were estimated through modeling except gender-specific asymptotes, which were fixed at
mean values calculated from yearling male (789 6 4 g, n 5 137) and female (719 6 6 g, n 5 54) Lesser
Prairie-Chickens captured in spring in southwestern Kansas.
DEVELOPMENT OF JUVENILE LESSER PRAIRIE-CHICKENS
93
TABLE 3. Predicted age (â) and 95% prediction intervals (PIL, PIU) for measurements of mass, foot length,
tarsometatarsus length, and wing length of Lesser Prairie-Chickens from southwestern Kansas. Age was estimated
using inverse Gompertz and logistic equations at arbitrarily selected morphometric measurements.
Mass
size
(g)
20
30
40
50
60
70
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
420
460
500
â
4.6
9.6
13.2
16.1
18.4
20.4
22.2
25.3
27.8
30.1
32.1
34.0
35.7
37.3
38.9
40.3
41.8
43.2
44.6
45.9
47.3
48.7
51.5
54.4
57.6
Foot
PIL PIU
4
9
13
16
18
20
22
25
27
29
31
33
34
36
37
39
40
41
42
44
45
46
49
52
54
10
13
16
19
21
23
24
27
30
32
34
36
38
40
41
43
44
46
47
49
50
52
55
58
61
length
(mm)
â
20
22
24
26
28
30
32
34
36
38
40
42
44
–
–
–
–
–
–
–
–
–
–
–
–
2.8
5.5
8.1
10.7
13.3
15.9
18.6
21.5
24.5
27.7
31.2
35.3
40.0
–
–
–
–
–
–
–
–
–
–
–
–
Tarsometatarsus
PIL PIU
length
(mm)
â
PIL
22 10
0 13
3 15
6 18
8 21
11 25
14 28
16 32
19 36
22 44
25 67
29 106
34 120
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
–
–
–
–
–
–
–
–
1.8
4.2
6.6
8.8
11.1
13.3
15.5
17.7
20.0
22.4
24.9
27.5
30.4
33.5
37.2
41.5
46.9
–
–
–
–
–
–
–
–
24
21
2
4
7
9
11
13
16
18
20
22
25
28
31
35
39
–
–
–
–
–
–
–
–
a decided tendency to lose this barring on the
inner half of the feather. We found the rectrices
of most known females prior to 60 days posthatching did not have uniform barring across the
feather vane on both sides of the rachis. Our
retrospective analysis suggests that gender of juvenile Lesser Prairie-Chickens can be identified
as early as 30 days post-hatching by examining
the barring on the outer half of the rectrices.
However, accuracy of this technique should be
tested on a larger sample of birds before it is
implemented in the field.
Measures of body mass, foot length, tarsometatarsus length, and wing length were pooled
across the three years of this project because of
small samples sizes; this may have decreased the
precision of estimating age of birds from changes in these parameters. Ricklefs (1968) observed
that growth of birds could vary annually due to
changes in weather or food availability and several grouse researchers have reported such variations (Myrberget et al. 1977, Lindén 1981,
Wing
PIU
length
(mm)
â
PIL
PIU
9
12
14
16
18
21
23
26
28
31
35
39
44
51
87
133
134
–
–
–
–
–
–
–
–
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
105
110
120
130
140
150
160
170
180
1.1
2.6
3.9
5.2
6.4
7.6
8.7
9.9
11.0
12.1
13.2
14.3
15.4
16.5
17.7
18.9
20.1
21.3
24.0
26.9
30.3
34.2
39.0
45.5
56.1
21
1
2
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
21
23
26
29
34
39
47
5
6
7
9
10
11
12
14
15
16
17
19
20
22
23
25
26
28
72
43
140
129
136
145
147
Quinn and Keppie 1981, Erikstad and Andersen
1983). We observed a large variation in mass of
same-age chicks beyond 35 days post-hatching
and mass of chicks near 35 days post-hatching
ranged from 100 to 300 g. Much less variation
was observed in growth of foot length, tarsometatarsus length or wing length. These parameters may have been less affected by extrinsic
factors such as food availability or weather, as
compared to mass, however we did not collect
any data to substantiate such speculation.
Changes in body mass of White-tailed Ptarmigan from hatching to 30 days post-hatching
have also been modeled using linear regression
(Giesen and Braun 1979) but the parameters
were not comparable to growth rate constants
reported for other grouse species. Additionally,
age-specific wing length measurements were reported for White-tailed Ptarmigan (Braun et al.
1993) but no statistical modeling was used to
describe wing growth. Thus, we were unable to
compare morphologic characteristics between
94
JAMES C. PITMAN
ET AL.
TABLE 4. Comparison of growth rate parameters for six grouse species. Data presented include Gompertz
growth rate constants (K) and time (t) required for growth from 10 to 90% of the asymptotic adult body mass
(A).
Gendera
K
t
A (g)
M
0.053
57.4
789
Kansas
W
This study
F
M
M
F
F
0.051
0.029
0.034
0.053
0.059
60.6
108.3
91.9
57.0
50.7
718
3469
3880
1524
1532
Kansas
Finland
Finland
Finland
Finland
W
C
C
C
C
This study
Lindén 1981
Lindén 1981
Lindén 1981
Lindén 1981
B
0.034
91.8
825
Colorado
C
McEwen et al. 1969
Dendragapus obscurus
F
0.047
64.3
650
British Columbia W
Lagopus lagopus
Bonasa umbellus
B
M
0.065
0.042
47.5
74.0
650
590
Russia
New York
Species
Tympanuchus pallidicinctus
Tympanuchus pallidicinctus
Tetrao urogallus 1978
Tetrao urogallus 1979
Tetrao urogallus 1978
Tetrao urogallus 1979
Tympanuchus
phasianellus
Location
Datab
C
C
Source
Redfield and Zwickel
1976
Ricklefs 1973c
Ricklefs 1968d
a M 5 male, F 5 female, and B 5 both genders.
b C 5 captive raised birds, W 5 wild stock.
c Data from Dement’ev and Gladkov (1952).
d Data from Bump et al. (1947).
Lesser Prairie-Chickens and White-tailed Ptarmigan.
However, changes in Lesser Prairie-Chicken
body mass were comparable to five other grouse
species for which growth rates had been previously reported (Table 4). The pooled-mass model developed in our study fits the data well for
the first 65 days post-hatching, but does not provide a good depiction of growth up to maturity.
Thus, our estimated constant does not accurately
represent overall growth of Lesser PrairieChickens. The growth rate constants derived
from the gender-specific mass models are most
appropriate for comparing Lesser Prairie-Chicken mass gains to other grouse species because
the asymptotes were fixed at values representative of males and females in our study. Growth
rate constants derived from the Gompertz and
logistic equations are not directly comparable so
all data were converted to the Gompertz form
(Ricklefs 1973) and values generated in this
study were compared to those from five other
grouse species (Table 4).
Mass gains of Lesser Prairie-Chickens and the
five other grouse species tend to support an inverse relationship between asymptotic body size
and growth rate reported by Ricklefs (1973) for
precocial birds (Table 4). The male of the largest
grouse species, Capercaille (Tetrao urogallus),
has the slowest growth rate and requires the longest time period to grow to 90% of asymptotic
size. When compared to the Capercaille, the
growth rate constants of male and female Lesser
Prairie-Chickens are nearly two-fold greater. The
time required to achieve 90% of the asymptote
is much less for male and female Lesser PrairieChickens than for Capercaille, which further
supports the findings of Ricklefs (1973). However, not all of the reported growth rate constants
follow this trend. The larger Willow Ptarmigan
(Lagopus lagopus) and female Capercaillie both
grow quicker than the smaller Ruffed Grouse
(Bonasa umbellus; Table 4). This discrepancy
could be related to adaptive growth strategies for
birds at different latitudes or the quality of data
used in the modeling processes. A Gompertz
growth rate constant has only been calculated
for Blue Grouse (Dendragapus obscurus) and
Lesser Prairie-Chicken using data from wildcaptured birds. Growth rates derived for the other four species used data collected from captivereared birds, and may not mimic the growth of
wild birds (Redfield and Zwickel 1976). Comparisons that are more meaningful will be possible only when more growth rate data are available from wild populations of other grouse species.
DEVELOPMENT OF JUVENILE LESSER PRAIRIE-CHICKENS
ACKNOWLEDGMENTS
J. O. Cattle Co., Sunflower Electric Power Corporation, Thornton Cattle Co., Brookover Cattle Co., R. A.
Greathouse, and the P. E. Beach family provided property access. G. C. Salter assisted with field work. We
thank C. E. Braun and one anonymous reviewer for
comments that substantially improved the manuscript.
This study was supported by Kansas State University
(KSU), Division of Biology; KSU Agricultural Experiment Station (Contribution 04-133-J); KDWP, Federal
Aid in Wildlife Restoration Project W-53-R; and Westar Energy, Inc.
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