DOI: 10.5061/dryad.0000000fz
title: Feather nitrogen and carbon stable isotope (d15N and d13C) values for Golden-crowned Sparrows

description: 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. 
description: We collected feathers in the months of October-March from
 individuals at five study sites across the Golden-crowned Sparrow
 wintering range (western regions of Canada and the United States) from
 2019-2021. We collected 8-10 contour feathers for genetic sexing and two
 outer tail feathers (rectrices) for stable isotope analysis. Due to
 funding limitations, we were only able to genetically determine sex for a
 subset of the birds with stable isotope information, leaving some birds
 with stable isotope values but unknown sex. We used wing chord values to
 sex an additional 13 birds (see paper for additional details), for a total
 of 73 individuals with stable isotope values and an assigned sex. Feathers
 were processed at the Cornell Isotope Laboratory at Cornell University,
 Ithaca, NY, USA. 
description: # Feather nitrogen and carbon stable isotope (d15N and d13C) values for
 Golden-crowned Sparrows Dataset DOI:
 [10.5061/dryad.0000000fz](10.5061/dryad.0000000fz) ## Description of the
 data and file structure The data includes stable isotope values of carbon
 and nitrogen (d15N and d13C) collected from feathers (outer rectrices) of
 Golden-crowned Sparrows. Where known, age, wing chord length (mm), and
 mass (g) are provided, as well as the wintering location where feathers
 were collected. Sex is given, as well as how sex was determined (i.e.,
 genetically or using wing-chord lengths).  ### Files and variables ####
 File: GCSP\_isotope\_data.csv ##### Variables * Band_no: Federal band
 number * feath_coll_loc: Where the feathers were collected. This includes
 Parksville on Vancouver Island, British Columbia, Canada (PABC), the
 University of California, Davis campus, Yolo County (UCD), Hagmaier Ranch
 in Olema Valley, Point Reyes National Seashore, Marin County (HAGM),
 Malibu, Los Angeles County within the Santa Monica Mountains National
 Recreation Area (ZUMA), and in Newcastle, California, in Placer County
 (NEWC) * Feath_coll_date: The date the feathers were collected in
 MM/DD/YYYY format.  * know_orig: Whether or not the origin is known for
 where feathers were grown, assuming feathers were grown at breeding
 grounds during normal prebasic molt. This is for a subset of birds that
 had been tracked with GPS.  * age: Age of birds. AHY = After hatch year;
 ASY = After second year; SY = Second year. * wing_mm: Wing chord length of
 birds in mm. NA =  measurement not available.   * mass_g: Body mass of
 birds in grams  * Sex: Male or female * sample_weight_mg: Weight of the
 sample for stable isotope analysis, in mg  * N2_Amp: The amplitude of the
 sample peak in mV of N2  * perc_N: The elemental percentage of nitrogen
 based on weight * d15N: The corrected isotope delta value for 15N measured
 against a primary reference scale (atmospheric air) * CO2_Amp: The
 amplitude of the sample peak in mV of of CO2 * perc_C: The elemental
 percentage of carbon based on weight * d13C: The corrected isotope delta
 value for 13C measured against a primary reference scale (Vienna Pee Dee
 Belemnite) * batch_paper: The batch the samples were run in at the lab
 where the number refers to the appendix of the associated manuscript and
 gives values for standards that were run during processing  * how.sexed:
 If genetic, feathers were processed at a lab to determine sex. If
 assigned, sex was determined based on wing chord length, following a
 process described in the associated manuscript