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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 124. No. 3. September 2012 
by between-year variation in types of females 
sampled, population density, and other aspects of 
resource abundance and predation pressure 
(McLoughlin and Ferguson 2000). We cannot rule 
out these possible effects, but the density of the 
study population as measured by the total number 
of nests found (1998 = 154: 1999 = 163; 2007 = 
120) and number of breeding pairs (1998 = 75: 
1999 = 78; 2007 = 72) was slightly higher during 
the fertile period study (1998, 1999) than during 
the nestling period study (2007). We predicted 
decreased density to cause larger home ranges due 
to decreased competition for space (Hooper et ul. 
1982, Anich cl al. 2010), but females still had 
significantly smaller home ranges during the 
nestling period despite lower densities. 
The decline in female home-range si/c between 
the fertile and nestling stages can potentially be 
attributed to a transition from nest building and 
seeking copulations during the fertile period, 
which often causes females to leave their social 
mate's territory (Stapleton and Robertson 2006, 
Whitaker and Warkcntin 2010), to focus on 
parental care and nest defense during the nestling 
period. We quantified female movements from 
days 3 to 5 of nestling life, likely before nestlings 
could thermoregulate independently (Dawson 
et al. 2005) and females were still frequently 
brooding. The junco nestling period lasts 1 I to 
12 days before fledging, and females are known to 
decrease their time spent brooding by as much as 
75% between days 4 through 7 and days 8 through 
10 of nestling life (Wolf et al. 1990). Female 
home-range size may expand during the second 
half of the nestling period as females spend less 
time brooding and potentially take advantage of 
more distant resources. 
Previous estimates of male Dark-eyed Junco 
home-range size in our study population indicated 
that males do not differ delectably in home-range 
size across the nesting cycle (Chandler et al. 1994, 
1997), which contrasts with our result for females. 
Male home-range size (mean ± SD.i during the 
nestling period (1.31 ± 0.525 ha: Chandler et al. 
1994) was larger than our estimate of female 
home range during the nestling period (0.833 ± 
0.788 ha), but this difference was not statistically 
significant (Two-sample Kolmogorov-Smimov 
Test; Z = 1.220; P = 0.102). Male and female 
juncos pertorm approximately an equal amount 
ot provisioning throughout the nestling period 
(Ketterson et al. 1992), which may contribute to 
the similarity in home-range size. Female juncos 
maintained a slightly larger (mean ± SD) home- 
range size during the fertile period (2.44 = 
0.992 ha: Ncudorf et al. 2002) than males (2.11 
— 0.539 ha; Chandler et al. 1997). which may 
explain why females have a significant decline in 
home-range size between the fertile and nestling 
stages while males do not. 
Female juncos exhibited substantial individual 
variation in home-range size during the nestling 
period suggesting not all females were minimiz¬ 
ing distance traveled from the nest, despite the 
increased energetic costs and potential spatial 
constraints associated with nestling care The 
observed variation could be a product of among 
home-range variation in resource availability 
(Moller 1990, Rolando 2002). The largest and 
smallest home ranges in our study were in the 
same general area of the study site (~ 350 in 
apart) and no large-scale differences (e.g.. hole! 
property vs. mature forest) in habitat characteris¬ 
tics were observed betw-ecn these two territories. 
There may be finer scale differences in habitat 
quality contributing to these large differences in 
home-range size. For example, juncos are known 
to roost exclusively in coniferous trees (Chandler 
et al. 1995) and, in our study, females appeared to 
preferentially forage in and around hemlock 
(Tsuga spp.) (DGR. pers. obs.). One explanation 
lor the large differences in home-range size over a 
relatively small spatial scale may relate to 
differences in distribution of hemlock. Thus, 
identifying the relative importance and distribu¬ 
tion of limited resources within a home range, 
such as hemlock trees, is an important topic for 
future studies of avian spatial activity. Future 
studies should also compare the spatial activity ot 
individual females across the nesting cycle to 
control for individual variation between females 
and years. 
ACKNOWLEDGMENTS 
We thank S. E. Schrock. D. M. O’Neal. N. M. Gerlach. 
K. L. Gray son. Jcrrah Jackson. Christina Jenkins, J. J. Pnce. 
and Erin Spcvak for assistance in the field. E. A. Snajdf and 
E. M. Schultz also provided Held assistance and summa¬ 
rized nesting and pairing data, V. A. Formica, E. S. Nagy 
and R. Ci. Thurau provided crucial technical support with 
the (iPS equipment and GIS software. Four anonymous 
reviewers provided comments that improved the manu¬ 
script. We also thank the director at Mountain Lake 
Biological Station. E. D. Brodie lit, the Mountain Like 
Motel, and the Uolinger Family for allowing us to work on 
their property. This study was funded by a National Science 
Foundation Grant to EDK (IOB-05-19211). 
