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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 3. September 2011 
(net/m/hr) and higher observed migrant diversity. It 
is possible the APBP and other inland pine barrens 
are used as stopover sites simply because they have 
remained undeveloped islands of habitat in the 
expanding sea of suburban sprawl. Future research 
directed at addressing the relative importance of 
pine barrens as stopover sites should include 
controlled comparisons with similar size, nearby 
forests, agricultural landscapes, and riparian areas. 
The list of species we captured surely under¬ 
estimates the true diversity of autumn migrants 
that use the Albany Pine Bush Preserve as a 
stopover site. Species such as Wilson’s Warbler 
(Wilsonia pusilla) and Fox Sparrow (Passerella 
iliaca) are represented by single captures, sug¬ 
gesting species diversity probably would increase 
if survey effort were greater. One of the primary 
limitations of mist netting as a survey tool is the 
bias toward capturing birds dial forage mostly in 
the 2 m of vegetation closest to the ground 
(Remsen and Good 19%). This bias is probably 
less severe in the low-growing pitch pine-scrub 
oak habitat on the APBP than in forested habitats 
with higher strata available to feeding birds. 
Despite its limitations, our mist-net surveys 
expanded the list of bird species known to occur 
on the Albany Pine Bush Preserve (Barnes 2003. 
Gifford et al. 2010) and led to its designation in 
2008 as a New York State Bird Conservation Area 
(McGowan and Corwin 2008). 
Our hydrogen isotope analysis of the timing of 
stopover at the APBP with respect to latitude of 
breeding origin failed to reveal any correlation 
between stopover date and breeding latitude for 
our six target species (Fig. 3). Previous research 
(Kelly et al. 2002. Kelly 2006) has shown both 
negative and positive correlations for different fall 
migrating warbler species that stopover at the 
Bosque del Apache National Wildlife Refuge in 
New Mexico; some species (Orange-crowned 
Warbler (Oreothlypis celata], Common Yellow- 
throat [Geothlypis trichas\) breeding at southern 
latitudes arrived earlier than birds breeding at 
northern latitudes, whereas for other species 
(Yellow Warbler [Dendraica petechia], Wilson’s 
Warbler) the reverse was true. Our failure to find 
any trends by our six study species may be due to 
our small sample size, although Kelly et al. (2002) 
had similar sample sizes of Common Yellow- 
throat („ - 19), Orange-crowned warbler (n - 
17), and Yellow Warbler (« = 18). Ours is the 
first attempt to use the hydrogen isotope approach 
characterize the chronology of migration within 
species in eastern North America, and our results 
indicate migration through eastern North America 
is less geographically structured than in the 
western U.S. Several other fundamental differ 
ences exist between the eastern and western 
songbird migration systems (Kelly and Hutto 
2005) including taxonomic composition, relative 
use of fat metabolism, diet, and habitat use. 
Movement patterns are also apparently highly 
variable among passerine species (Kelly et al. 
2002, Kelly 2006), and fall migration may be 
geographically structured in other species that 
pass though our study site. 
The isotope data indicate catchment areas for 
all six study species were large and extended to 
regions of the boreal forest hundreds of kilometers 
from our study site (Fig. 4). This finding is similar 
to previously reported catchment areas estimated 
for other species of passerines at migration 
monitoring stations in Manitoba (Wassenaar ami 
Hobson 2001, Mazerolle et al. 2005) and southern 
Ontario (Wassenaar and Hobson 2001). Thus, 
catchment areas of migratory stopover sites vary 
considerably among species. The estimated catch¬ 
ment areas of five of our six study species 
included regions north of the APBP, and extend¬ 
ing well to the east and west (Fig. 4). The isotope 
approach does not allow distinguishing among all 
potential source areas within a given 8/) p contour, 
Thus, it is not possible to identify how far east or 
west the birds that stopover on the APBP may 
originate. Most passerine species migrate in a 
generally north-south direction that parallels 
mountain ranges, major river valleys, and coast¬ 
lines. We suspect the catchment areas we mapped 
overestimate the western extent of true catchment 
areas, and populations originating near the 
western edge of our catchment areas are not 
passing through APBP. An exception may be the 
Blackpoll Warbler, which has a unique trans¬ 
oceanic migratory pathway (Nisbet et al. 1995. 
Hunt and Eliason 2001). Individual Blackpoll 
Warblers migrate in a general eastward direction, 
collecting along the Atlantic Coast in Maritime 
Provinces and the northeastern United States. 
Blackpoll Warblers then migrate over the Atlantic 
Ocean to wintering areas in northern South 
America. Our data support the hypothesis that 
individuals breeding just north and east of the 
APBP in New York, New England. Ontario, and 
the Maritime Provinces do not pass through APBP 
as they migrate east. 
Our hydrogen isotope analysis of six species 
