Full lifetime perspectives on the costs and benefits of lay date variation in tree swallows

WINKLER, DAVID W.; HALLINGER, KELLY; PEGAN, TERESA; TAFF, CONOR; VERHOEVEN, MO A; VAN OORDT, DAVID CHANG; STAGER, MARIA; UEHLING, JENNIFER J.; VITOUSEK, MAREN; ANDERSEN, MICHAEL; ARDIA, DAN; BELMAKER, AMOS; FERRETTI, VALENTINA; FORSMAN, ANA; GAUL, JENNIFER; LLAMBIAS, PAULO E.; ORZECHOWSKI, SOPHIA; SHIPLEY, RYAN; WILSON, MAYA; HYUN SEOK YOON

ECOLOGY

ECOLOGICAL SOC AMER

Año: 2020

0012-9658

Animals must balance various costs and benefits when deciding when to breed. The costs andbenefits of breeding at different times have received much attention, but most studies have beenlimited to investigating short-term season-to-season fitness effects. However, breeding early, versuslate, in a season may influence lifetime fitness over many years, trading off in complex ways acrossthe breeder?s lifepan. In this study, we examined the complete life histories of 867 female treeswallows (Tachycineta bicolor) breeding in Ithaca, New York, between 2002 and 2016. Earlierbreeders outperformed later breeders in short-term measures of reproductive output and offspringquality. Though there were weak indications that females paid long-term future survival costs forbreeding early, lifetime fledgling output was markedly higher overall in early-breeding birds.Importantly, older females breeding later in the season did not experience compensating life-historyadvantages that suggested an alternative equal-fitness breeding strategy. Rather, most or all of theswallows appear to be breeding as early as they can, and differences in lay dates appear to bedetermined primarily by differences in individual quality or condition. Lay date had a significantrepeatability across breeding attempts by the same female, and the first lay date of females fledged inour population was strongly influenced by the first lay date of their mothers, indicating the potentialfor ongoing selection on lay date. By examining performance over the entire lifespan of a largenumber of individuals, we were able to clarify the relationship between timing of breeding and fitnessand gain new insight into the sources of variability in this important life history trait.