Skip to main content
Dryad

Elevational differences in migration phenology of Lazuli Buntings do not support selection-based hypotheses for protandry

Data files

Jun 21, 2023 version files 394.28 KB

Abstract

Documenting and understanding sex-specific variation in migratory phenology is important for predicting avian population dynamics. In spring, males often arrive on the breeding grounds before females (protandry), though whether these patterns result from fitness benefits versus sex-specific constraints on arrival timing remains poorly understood. Sex-specific variation in the timing of fall migration is less well-documented than in spring, in part because documenting fall departures is often limited by cryptic behaviors, lower vocalization rates, and shifting territory boundaries during this time of year. We used two years of high-resolution encounter data from radio-frequency identification (RFID)-equipped bird feeders to monitor the daily presence of male and female Lazuli Buntings (Passerina amoena) throughout the breeding season at a high and a low elevation site in Cache County, Utah, USA. These encounter data were used to estimate daily arrival and departure probabilities and to investigate possible differences in migration timing in relation to sex and elevation. At low elevation, male arrival (n=15) preceded female arrival (n=16) by approximately one week, consistent with previous research that has documented protandry in other migratory songbirds. At high elevation, however, no significant differences were found between male (n=19) and female arrival (n=6). In fall, we found little difference in departure dates between elevation or sex, or between years.  Our observations are most consistent with constraint-based hypotheses explaining protandry, possibly relating to sex-specific constraints operating during the non-breeding period. We additionally emphasize the need for quantifying uncertainty in phenological estimates and importance of addressing potential differences across demographic groups.