Sex Ratio Observed in White Crowned Sparrow Population (Zonotrichia leucophrys gambelii) Wintering at the Bernard Field Station

Differential migration is when a subset of a population, usually an age or sex group, migrate different distances or at different times. Gambel’s White Crowned Sparrows (WCSP), have been recorded as exhibiting sex-based migration. To test the fidelity of this phenomenon we performed PCR and gel electrophoresis to determine the sex-ratio of WCSP during their non-breeding season, in the winters from 2017-22, at the Bernard Field Station in Claremont, California. Previous studies have observed a male-biased sex ratio at locations north of our study site and female-biased sex ratio at locations south of our site. Based on this latitudinal cline observed in WCSP sex-ratio, we expected to see a female-biased population. A chi-squared test was run on 193 banded individuals and a separate chi-squared test was run on the individuals observed within each year. The results showed that the ratio of males to females did not differ from 1:1. Overall or within any given year of the study 50% female and 50% male was observed in the population. Our preliminary findings suggest that there are other factors that influence inter-population spread of differential migrants. Knowledge of differential migration is important for understanding how ecological conditions in isolated areas could have unequal effects on subgroups within migrant species