2005
SOUTHEASTERN NATURALIST
4(4):639–646
Factors Affecting January Reproduction of
American Woodcock in Texas
R. MONTAGUE WHITING, JR.1, DAVID A. HAUKOS2, AND LOREN M. SMITH3,*
Abstract - Scolopax minor (American Woodcock) populations have been declining
for the past several decades. Weather conditions have been hypothesized to affect
reproductive efforts in February and March in the southern United States, but similar
influences on January breeding activities are unknown. We used a 17-year harvest
data set from eastern Texas to examine the influence of several temperature and
precipitation measures, female body mass, and forest habitat type on the occurrence
of reproduction by Woodcock in January. Only adult females exhibited characteristics of breeding activity. There was annual variation (0–29%) in the occurrence of
breeding adult females, but local temperature and precipitation measures were not
correlated with January reproduction. More breeding Woodcock were harvested in
open sapling stands than other habitats. Environmental factors other than monthly
temperature and precipitation may influence January reproductive efforts of Woodcock in eastern Texas. We suggest investigation of timing of fall migration and
condition of the birds upon arrival on wintering grounds as potential factors influencing reproductive efforts in January.
Introduction
Scolopax minor Gmelin (American Woodcock) populations have been
declining for many years in the United States (Dwyer et al. 1983, Straw et al.
1994). Singing-Ground Survey data indicate a decline of 2.1% per year in
the Eastern Region and 1.8% annual decline in the Central Region since
1968 (Kelley 2004). The Parts Collection Survey, where wings collected
from hunters are used to estimate the number of young per adult female, also
indicates a decline in recruitment since the mid-1980s (Kelley 2004). As a
result of these declines, hunting season lengths and bag limits have been
reduced (Dwyer and Nichols 1982, Keppie and Whiting 1994).
Because of the consistent long-term decline in Woodcock numbers, factors
potentially influencing recruitment of this species should be investigated.
Associated with the population decline, the documented decreasing recruitment indices indicate that reproduction may be a factor in the population
dynamics of Woodcock. Woodcock often nest in the southern United States
during late winter and early spring, exhibiting nesting activities starting in
January through April (Roboski and Causey 1981, Whiting and Boggus 1982,
Whiting et al. 1985). However, there is considerable annual variation in nesting
1
Arthur Temple College of Forestry, Stephen F. Austin State University,
Nacogdoches, TX 75962. 2United States Fish and Wildlife Service, Department of
Range, Wildlife, and Fisheries Management, Texas Tech University, Lubbock, TX
79409. 3Wildlife and Fisheries Management Institute, Texas Tech University, Lubbock, TX 79409. *Corresponding author - l.m.smith@ttu.edu.
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efforts of Woodcock in the South (Causey et al. 1987, Olinde and Prickett 1991,
Walker and Causey 1982), and the factors influencing the frequency and
occurrence of that reproductive effort are not well understood. In Alabama,
Woodcock nesting activity has been related to temperatures during January;
warmer temperatures (number of days with mean daily temperature ≥ 4.4 °C)
were associated with increased reproductive effort (Causey et al. 1987).
However, previous studies have concentrated on the February–April period
while the January nesting effort has remained uninvestigated.
Whiting and Boggus (1982) suggested that only adult females attempt to
breed in eastern Texas and hypothesized that a minimum body mass of 210 g
was necessary to initiate nesting. They further suggested that body mass gain
during winter was necessary to achieve the minimum body mass level.
Potential factors influencing body mass of wintering Woodcock include soil
moisture, which affects the availability of prey (i.e., earthworms), and habitat type (Boggus and Whiting 1982). Using 17 years of harvest data, our
objective was to examine the influence of December and January temperatures, several measures of precipitation, female body mass, and habitat type
on the occurrence and frequency of January nesting activities by American
Woodcock in eastern Texas.
Field Site Description
All Woodcock used in this study were harvested in the Pineywoods
Ecological Region of eastern Texas (Gould 1969). Most (approximately 99%)
birds were harvested in Angelina, Houston, Nacogdoches, Sabine, San Augustine, Shelby, and Trinity Counties on private (≈ 50%) and United States
Forest Service (≈ 50%) lands. Woodcock were harvested in a variety of upland
habitats, ranging from 1-year-old pine plantations to 80-year-old mixed pinehardwood stands. All seedling (< 3 years old) habitats were planted Pinus
taeda L. (loblolly pine) or P. enchinata P.Mill. (shortleaf pine) plantations.
Some sapling and pole stands had been planted, others resulted from seed tree
regeneration harvests. All sawtimber stands were from natural regeneration.
Although each habitat was dominated by loblolly or shortleaf pine, all had a
hardwood component (e.g., Quercus spp.). Similarly, all occurred on soils that
are generally classified as sandy loams or loamy sands.
Methods
Woodcock were collected by shooting during January, consistent with
existing hunting seasons, from 1986–1987 to 2002–2003. Woodcock were
aged and sexed based on wing characteristics (Martin 1964). We weighed all
individuals to nearest 1.0 g. Each harvested female was examined for evidence of reproductive activity. We classified individuals as breeders if they
were flushed from a nest (n = 4), had an enlarged cloaca indicative of egg
laying, or contained developing eggs in the reproductive tract or ovarian
follicles in the rapid-eruption stage upon internal examination (internal/
external n = 36; Whiting and Boggus 1982). We classified forest habitat type
2005
R.M. Whiting, Jr., D.A. Haukos, and L.M. Smith
641
in which each female was harvested as: 1) young seedling—pines and
hardwoods < 2 m tall; 2) old seedling—up to 25% of pines and hardwoods
were > 2 m tall; 3) open sapling—pines and some hardwoods were > 2 m tall,
but pine canopy closure was minimal; 4) closed sapling—pines and some
hardwoods were 2–4 m tall and canopy closure was 25–75%; 5) open pole—
pines and some hardwoods were > 4 m tall and canopy closure was < 50%;
6) closed pole—canopy generally closed; 7) small sawtimber—dominant
pines generally > 20 cm and < 30 cm diameter at breast height (dbh); and 8)
large sawtimber—pines and some hardwoods > 30 cm dbh.
We obtained local precipitation and temperature data (Lufkin, TX) from
National Oceanic and Atmospheric Administration sources
(www.ncdc.noaa.gov/oa/climate). For each year (1987–2003), we determined: 1) the number of days in December of the previous year and January
when the mean daily temperature was > 4.4 °C; 2) average previous November, previous December, and January temperatures; 3) January rainfall total;
4) rainfall total for the previous months of October, November, and December; and 5) total precipitation of the previous year.
Statistical analyses
For each year of collection, we determined age of collected females that
exhibited reproductive characteristics in January (Fig. 1). We used a forward
stepwise linear and logistic multiple regression approach (variable entry and
exit P = 0.15) to examine the influence of environmental variables on the
annual percent (linear) and occurrence (logistic) of nesting females (PROC
REG; SAS Institute 1999). We used correlation analyses to examine the
relationship of each environmental variable on the annual percent of breeding females (Pearson option, PROC CORR; SAS Institute 1999). We also
used a two-way factorial analysis of variance to compare: 1) body mass
between breeding and nonbreeding females among years, and 2) body mass
between breeding and nonbreeding females among habitat types (PROC
GLM; SAS Institute 1999).
Results
Only adult female American Woodcock exhibited characteristics of nesting in eastern Texas (Table 1). Therefore, we restricted further analyses to
adult data. Of 539 adult females harvested from 1987–2003, 40 (7.4%) were
classified as breeding. Breeding birds were harvested between 12 January
and the last week of the month. There was considerable annual variation in
the number of adult females breeding during January, ranging from 0% in 7
years to 28.6% in 1997 (Table 1).
There was no interaction (F10,513 = 1.42, P = 0.17) between breeding
status and year for body mass. Body mass differed (F1,513 = 151.6, P < 0.001)
between breeding (mean = 225.3 g, SE = 1.9, n = 40) and nonbreeding adult
females (mean = 195.6 g, SE = 0.6, n = 499). Five breeding females (12%)
weighed < 210 g, with the lowest mass of a breeding female being 205 g (a
bird that recently completed her clutch). Body mass of adult females differed
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among years with 1997 and 2000 representing the mass extremes (F16,513 =
2.18, P = 0.005; Table 1).
We found little relationship between nesting and either precipitation or
temperature variables. The best-supported linear regression model (adj. R2 =
0.14, F = 2.31, P = 0.13) relating the percent of nesting females and
environmental factors included number of days in December when the daily
average temperature was > 4.4 °C and total previous November–December
precipitation. However, regression coefficients for both variables (-0.78 and
-0.63, respectively) were negative. Annual percent of nesting adult females
was independent of: the respective number of days in December and January
when daily average temperature was > 4.4 °C (r17 = -0.31, P = 0.22; r17 =
-0.01, P = 0.97, respectively); average November, December, and January
temperatures (r17 = 0.05, P = 0.85; r17 = -0.09, P = 0.73; r17 = 0.16, P = 0.54,
respectively); January precipitation (r17 = 0.24, P = 0.35); November–December precipitation (r17 = -0.33, P = 0.19); and total precipitation of the
previous year (r17 = -0.15, P = 0.56).
There was no interaction (F6,526 = 0.81, P = 0.56) between adult female
breeding status and habitat type for body mass. Body mass of females was
Figure 1. Number
of
hatch-year
(HY) and afterhatch-year
(AHY) harvested
female American
Woodcock during
January 1987–
2003 in eastern
Texas.
33
16
27
20
9
19
26
41
43
29
43
41
33
34
31
193–202BCDE
188–206BCDE
197–206B
193–206BCD
189–203BCDE
184–201EF
195–211BC
189–197DEF
204–212A
192–201BCDE
191–199CDE
184–193F
197–205BC
191–199CDE
190–197DEF
2.1
4.1
2.1
3.2
3.0
3.9
3.5
2.1
1.9
2.4
2.0
2.2
2.0
2.1
1.8
197.4
197.0
201.9
199.5
195.7
192.7
201.4
193.2
208.8
196.1
195.2
188.7
200.7
195.2
193.5
33
19
28
22
9
20
29
41
60
33
44
41
35
38
31
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
198.6
193.6
193.5
192.8
194.5
188.7
197.9
193.2
204.0
196.9
195.7
190.2
197.4
191.3
200.7
199.2
200.0
1.5
2.0
1.8
1.7
2.0
2.2
2.9
2.1
1.8
2.9
3.0
3.0
2.1
2.7
1.8
2.7
2.6
SE
Nonbreeding
mean
Means followed by the same uppercase letter do not differ among years (ANOVA, P > 0.05).
Both individuals had the same measured mass.
b
a
23
31
193–204
195–205BC
2.7
2.6
199.2
200.0
BC
25
31
n
1987
1988
95% CLa
SE
mean
n
Year
Total adult females
196–202
189–198
190–197
189–196
191–198
184–193
192–204
189–197
200–208
190–203
189–203
184–196
193–202
186–197
197–204
194–205
195–205
95% CL
2
4
0
4
1
0
3
0
17
2
0
1
0
3
1
2
0
n
218–229
234.0b
208.5
10.1
188–228
200–239
2.6
9.7
223.6
219.5
224.0
218–256
222–230
205–249
196–241
95% CL
9.6
2.0
11.2
11.5
SE
237.3
242.0
226.0
227.3
234.0
218.5
mean
Breeding
Table 1. Average annual body mass (g) of breeding and nonbreeding adult female American Woodcock harvested during January from 1987–2003 in
eastern Texas.
2005
R.M. Whiting, Jr., D.A. Haukos, and L.M. Smith
643
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similar (F7,526 = 1.56, P = 0.14) among habitat types. We harvested a higher
ratio of breeders in open sapling stands (Table 2). We collected higher ratios
of nonbreeders in closed sapling, open pole, closed pole, and large sawtimber stands than in other habitats.
Discussion
Although the number of breeding females was low in most years, during
some years, a large percent of adult females were reproductively active
during January in eastern Texas. Because data could only be collected in an
observational form versus an experimental form (i.e., we could not manipulate weather or body mass), findings should primarily be considered
correlations. Only adult female Woodcock exhibited characteristics of
breeding activity, supporting earlier findings of Whiting and Boggus (1982).
Walker and Causey (1982) also reported that all nesting Woodcock in
Alabama were adults. They attributed this to the superior ability of adults,
compared to juveniles, to respond to conditions conducive to breeding,
which was considered to be increased January temperature.
During this study, on average, 7.8% of adult females exhibited breeding
characteristics. This value is higher than that reported by Whiting et al.
(1985). They internally examined 164 adult females collected in 5 southern
states during January of 6 years and recorded only 7 (4.3%) females with
enlarged ovaries; slightly over 35% of the 170 February harvested females
were gravid. Because the peak of Woodcock nesting activity in the South
occurs during February and March, our reported January percent of adult
females exhibiting signs of reproduction is therefore not indicative of the
entire nesting effort in the region. Our data indicate the potential for January
breeding, which we believe should be investigated to further understand the
importance of early breeding on the population dynamics of Woodcock.
We found considerable annual variation in nesting efforts of Woodcock
in eastern Texas. Other studies in the South have found similar results even
for February and March reproductive activity (Causey et al. 1987, Olinde
and Prickett 1991, Walker and Causey 1982). Some studies (Causey et al.
1987, Olinde and Prickett 1991) suggested that the variation was related to
Table 2. Occurrence of breeding and nonbreeding adult female American Woodcock among
habitats of harvest in eastern Texas during January 1987–2003.
Breeding
Ratio of
breeders/
nonbreeders
1
2
15
4
4
0
3
11
0.11
0.13
0.16
0.04
0.06
0.00
0.12
0.06
Number of harvested birds
Habitat type
Nonbreeding
Young seedlings < 2 m tall
Old seedlings, < 25% of trees > 2 m tall
Open saplings, < 25% of trees were > 2 m tall
Closed saplings, all trees were > 2 m tall
Open pole, canopy closed in > 50% of stand
Closed pole, canopy is closed
Small sawtimber
Large sawtimber
9
15
91
105
64
10
25
180
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R.M. Whiting, Jr., D.A. Haukos, and L.M. Smith
645
January temperatures, but they often examined nesting in February and
March. However, based on our 17 years of data, monthly temperature and
precipitation following fall arrival of Woodcock in eastern Texas were not
correlated with reproduction during January.
Our body-mass data support Whiting and Boggus’ (1982) hypothesis that
a minimum adult female body mass of 210 g was necessary to initiate
reproductive activity in eastern Texas. Earthworms are the primary prey of
wintering Woodcock (Gregory and Whiting 2000, Miller and Causey 1985).
Boggus and Whiting (1982) suggested that soil moisture affected availability of earthworms, which could be a determining factor in body mass dynamics of Woodcock in eastern Texas. Our inability to demonstrate a correlation
between precipitation and reproductive effort during January does not support this hypothesis.
Reproductively active adult female Woodcock may use different habitats
in eastern Texas than nonbreeding birds during January. Specifically, the
ratio of nesting females harvested was highest in open sapling habitats. Open
sapling habitat generally has a large hardwood component due to forest
management. Roboski and Causey (1981) reported that Woodcock nests
were found in mixed pine-hardwood stands; specifically, in open intermediate-aged, pole-timber stands and open-grown, maturing, sawtimber stands.
However, we believe overstory characteristics are probably less important in
nest-site selection than characteristics of the ground cover and proximity to
moist, soft soils in which chicks can forage.
Unfortunately, an explanation for use of habitats in eastern Texas is
currently unavailable; thus, further investigation into habitat selection by
winter breeding female Woodcock is needed. Based on our results, and on
previously published findings, we hypothesize that habitat conditions during
fall migration and upon arrival on wintering grounds may influence body
condition and subsequent reproductive efforts in January. We also hypothesize that patterns and timing of temperature and precipitation conditions
may have an important influence on Woodcock foods and subsequent reproduction activities not only in January but throughout the remainder of winter
and into spring.
Acknowledgments
Our wintering American Woodcock research in eastern Texas has been supported
by the Arthur Temple College of Forestry at Stephen F. Austin State University and
the United States Fish and Wildlife Service. We appreciate the suggestions of D.G.
Krementz and two anonymous referees.
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