Annual Apparent Survival Differs Between The Sexes, But Does Not Covary With Overwinter Latitude, In A Differentially Migrating Population Of Song Sparrows (Melospiza Melodia)
Abstract
Many animals display differential migration, where members of a population breed at the same site but overwinter different distances from the breeding grounds. Effects of overwintering latitude on apparent survival are difficult to study because only returning individuals can be sampled to assess overwinter latitude. I used stable isotope analysis of deuterium from 558 winter-grown claw tissue samples (δ2Hc) to examine the relationship between annual apparent survival and overwinter latitude in a differentially migrating population of Song Sparrows (Melospiza melodia). I integrated breeding-site capture histories of 383 song sparrows into a modified Cormack-Jolly-Seber model incorporating a hierarchical model of δ2Hc, then performed data analysis using a Bayesian framework via MCMC sampling to assess how apparent survival varies with overwinter latitude. Males had higher apparent survival and recapture probability than females, but overwinter latitude lacked association with apparent survival. These results help explain how differential migration is maintained in this population.