Feather nitrogen and carbon stable isotope (d15N and d13C) values for Golden-crowned Sparrows

Differential foraging by sex can have important implications for
understanding the ecology of a species. This can be especially difficult
to study through observations alone in sexually monomorphic species, such
as the Golden-crowned Sparrow (Zonotrichia atricapilla), and for species
in remote areas. We used nitrogen and carbon stable isotope analysis to
determine the relative trophic position between the sexes for 73
individuals for this migrant songbird with little known diet information
while breeding in remote locations of Alaska and northwestern
Canada.  We found that females had significantly higher values of
feather δ15N (mean 5.44 ‰; mean for males 4.54 ‰) after accounting for
year and feather collection location, and in a subset of GPS-tagged birds
with known breeding locations, after accounting for year, breeding
latitude, elevation, or distance to shoreline. We infer that females may
be foraging more items from a higher trophic level than males on breeding
grounds, which may reflect a physiological need to replace lost nutrients
from nesting.