Age and Sex Ratios Observed in Gambel’s White-Crowned Sparrows (Zonotrichia leucrophrys gambelii) at the Robert J. Bernard Field Station
Campus Only Senior Thesis
Bachelor of Arts
© 2023 Eliza R Kornfeld
Many avian species exhibit differential migration, in which distinct classes of a population travel different distances. The Gambel’s White-crowned Sparrow (Zonotrichia leucrophrys gambelii) (WCSP) has been known to exhibit sex-based differential migration, and various passerines differentially migrate by age. To assess whether Gambel’s WCSPs exhibit differential migration by age, sex, or an interaction of the two, we determined the sex and age ratios of a population of WCSPs at the Robert J. Bernard Field Station (BFS) in Claremont, California during each winter in 2017-2023. We identified the birds present utilizing mark-recapture and camera data, analyzed their sex with PCR and gel electrophoresis of blood samples, and determined their age from plumage. Previous studies of Gambel’s WCSPs identified a latitudinal gradient of increasing females north of the BFS, so we expected a female bias. We also anticipated a juvenile bias, with a stronger bias in males, as juveniles migrate farther than adults and the difference in arrival date at the breeding grounds is greater in males than females for numerous passerines. We compared the frequency of males and females as well as adults and juveniles in each year, and the proportion of adults and juveniles for males and females among years. Our data demonstrated no sex bias, a bias toward adults rather than juveniles, and no association between age and sex. Therefore, future research must explore whether the migratory ranges, breeding ranges, or migratory paths of WCSPs are changing due to climate change, habitat loss, or other factors.
Kornfeld, Eliza, "Age and Sex Ratios Observed in Gambel’s White-Crowned Sparrows (Zonotrichia leucrophrys gambelii) at the Robert J. Bernard Field Station" (2023). Scripps Senior Theses. 2006.
Available for download on Tuesday, April 29, 2025
This thesis is restricted to the Claremont Colleges current faculty, students, and staff.