Reproductive outcomes determine the timing of arrival and settlement of a single-brooded Nearctic-Neotropical migrant songbird (Catharus fuscescens) in South America

Abstract

The breeding seasons of Nearctic-Neotropical migratory songbirds are thought to be constrained by the temporal demands of subsequent seasons. In any population, a subset of adults may fail to fledge young despite repeated attempts, which may prolong reproductive effort. We used geolocators to track the single-brooded Veery (Catharus fuscescens) from a Delaware, USA, breeding site to South America and back, to examine how reproductive failure and the timing of reproduction affected the spatiotemporal aspects of the nonbreeding season. We also considered the effect of additional variables: Age, sex, time in population (i.e. experience), productivity, and nutrition via ptilochronology. We found that clutch completion date and reproductive success were significant predictors of South American entry and arrival date at first winter sites, respectively. Reproductive success also influenced the latitude of winter sites. For females only, there was a consequence of reproductive failure: Unsuccessful females entered South America later, and arrived at first winter sites later, than successful females. Although there was a trend for unsuccessful females to exit South America earlier the following spring, they did not arrive in Delaware earlier, nor were they more reproductively successful the following year. We found an effect of age and sex on the timing of South American exit. Females differed from males in the timing of fall migration in South America, the timing of South American exit, and the timing of arrival back in Delaware. Our finding that arrival and settlement of adult Veeries in South America is primarily determined by former reproductive outcomes, rather than age, sex, or life history experience, is consistent with the contention that the breeding season of single-brooded species is constrained by subsequent seasons. Our results have implications for conservation, considering that the effect of reproductive failure goes beyond reduced fecundity.