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WOS 2010 ~ ABSTRACTS p. 32
all 149 species [Prob (Ha|data)= 0.98]. On average, all species distributions have shifted approximately 58 km to the
north. Separating north and south movements we found the majority of species (n = 107) show a northern shift of
approximately 92 km and the remaining species (n = 42) have shifted south on average 40 km. The initial results of
our study are similar to recent studies and provide more support for climate driven range shifts among birds. Further
work will evaluate elevation changes, boundary changes and overall changes in status of breeding species in
Ontario.
P18 S The effectiveness of constant effort mist-netting in estimating abundance and reproductive success of a Wood
Thrush population. Laura M. Niczyporowicz and Todd J. Underwood, Dept. Biology, Kutztown Univ., and Roland
R. Roth, Dept. Entomology and Wildlife Ecology, Univ. Delaware, Newark, DE 19716
Despite the widespread use of Constant Effort Mist-Netting (CEM) to monitor population demographics of
landbirds, relatively little is known about the validity of CEM estimates for various species of birds. In this study,
we determined whether CEM was an effective way to gauge the abundance and reproductive success of a Wood
Thrush population. We used linear regression to compare estimates of Wood Thrush demographic variables
generated by CEM to actual demographic values measured by intense nest searching and monitoring in the same
area over a period of six years. The demographic variables compared were: number of males, number of females,
number of HY (Hatch Year) birds, number of AHY (After Hatch Year) birds, and the ratio of HY to AHY birds. All
CEM estimates were standardized as the number of captures per 100 net hours. We found that only the CEM
estimates for HY birds (r2 = 0.85, P < 0.01) and the ratio of HYs to AHYs (r2 = 0.68, P < 0.05) were significantly
related to actual values. CEM estimates of the three adult abundance variables were not significantly related to
actual values. In conclusion, constant effort mist-netting may only be useful in estimating Wood Thrush
demographic variables involving hatch year birds.
P19 Evaluation of breeding habitat quality for a population in decline: the Canada Warbler in northeastern Vermont.
Jameson F. Chace, Dept. Biology and Biomedical Science, Salve Regina Univ., Newport, RI 02840, and Steven D.
Faccio, Vermont Center for Ecostudies, Norwich, VT 05055
Canada Warbler (Wilsonia canadensis) populations have been in a 40-year decline and yet little is known about its
population ecology. We have studied a population of Canada Warblers in the Nulhegan Basin of the Silvio O. Conte
National Fish and Wildlife Refuge in northeastern Vermont since 2001. During 2002-2006 age structure ranged
from 5.6:1 to 1.5:1 of After Second Year (ASY) to Second Year (SY) breeding males, and 30% ASY and 15% SY
territorial males returned to the population each year. We measured the breeding habitat characteristics of 31
territories (21 paired and 10 unpaired with females) and 20 nonuse points near those territories in the same habitat
type at three locations. Canada Warbler male territories had a greater density of large (diameter > 2.5 cm) shrub and
sapling stems and a greater percent ground cover of moss than the unoccupied "nonuse" points. During focal periods
of observations (n=737), males sang significantly higher in vegetation than when they exclusively foraged. Density
of understory stems was found highly correlated with prey abundance. Pairing success, however, was not related to
any of the 25 vegetative characteristics measured on male territories. While pairing success (50%) and return rates
(25%) in northeastern Vermont are relatively lower than those found among other populations of migratory
warblers, population declines stemming from issues on nonbreeding grounds or during migration are probably more
important factors in the population decline than are issues related breeding site quality in northeastern Vermont.
P20 S The effect of Wood Thrush hosts on the survival of Brown-headed Cowbird eggs and nestlings. Ashley N.
Rathman and William P. Brown, Dept. Biology, Kutztown Univ., Kutztown, PA 19530, and Roland R. Roth, Dept.
Entomology and Wildlife Ecology, Univ. Delaware, Newark, DE 19716
Although parasitic Brown-headed Cowbirds (Molothrus ater) have a detrimental effect on a wide range of hosts,
cowbird fledging rates differ substantially among those hosts. The purpose of this study was to explore the effect of
Wood Thrush (Hylocichla mustelina) hosts on cowbird survival through each nest stage (egg laying to incubation,
incubation to hatching, hatching to fledging) as well as the overall survival rate from egg laying through fledging.
Based on published observations, cowbird fledging success among other forest species hosts also was compared to
our results. Reproductive data of individually marked Wood Thrushes, including brood parasitism data, were
collected in Newark, Delaware, from 1975-2006. These data were used to construct a life table for both cowbirds
and Wood Thrushes from egg laying through fledging. Chi-squared tests were used to determine the difference in
survival of nest contents between Wood Thrushes and cowbirds. Both cowbirds and Wood Thrushes survived better
during the incubation stage than during the laying and nestling stages. There was no difference in survival of
cowbird and Wood Thrush eggs from laying to incubation. Wood Thrushes survived better than cowbirds in the
incubation and nestling stages. Among a variety of forest-dwelling hosts, the success of cowbirds from egg laying
through fledging ranged from 0% (House Finches, Carpodacus mexicanus) to 68.5% (Red-eyed Vireo, Vireo
olivaceus); 21% of cowbirds in our study survived from laying through fledging. We suggest this wide range of
cowbird success among hosts may be due to host diet or differential mass among host species.