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

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 i..., Study Site and Species
We monitored breeding Lazuli Buntings (Passerina amoena) within the Bear River Range of Cache County, UT, USA (41.8° N, -111.7° W). The Lazuli Bunting is a sexually dimorphic, generalist songbird that breeds throughout the western United States. This species is a moderate-distance migrant, travelling to west-coastal Mexico via the Sonoran region, where it is thought to complete its annual pre-basic molt (Greene et al. 2020). Though they are highly omnivorous, Lazuli Buntings readily visit bird feeders when stocked with white millet (Panicum miliaceum), making them an excellent candidate species for use of RFID resighting. We collected data from April to September, during 2019 and 2020 on two study plots established at low (1450 m) and high (1930 m) elevation, located 24.5 km apart within the same canyon. Both study sites provide suitable habitat for Lazuli Buntings, with no observable differences in sex ratios or breeding densities. The sites did vary in their veg...,
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