Assessing the reproductive consequences of mate retention and pair bond duration in Thorn‐tailed Rayadito (Aphrastura spinicauda), a short‐lived, socially monogamous neotropical bird

Abstract

The adaptive value of mate retention has been studied in several socially monogamous birds but evidence of reproductive benefits for short‐lived species is inconclusive. Most studies come from northern latitudes but more research on tropical birds is needed, as these species typically show higher survival rates and longer pair bonds than those from temperate regions. We gathered data on the reproductive biology of a subtropical, isolated population of Thorn‐tailed Rayadito Aphrastura spinicaudaduring 2008–2017 to evaluate the reproductive consequences of mate retention. We examined data from 243 breeding attempts made by 159 breeding pairs. We found that ~30% of all breeding pairs bred together during at least two consecutive years, and some were mated for 6 years. The main cause of pair dissolution was mate loss, not divorce. Mixed‐effects models provided moderate evidence for positive effects of mate retention and successive remating on reproductive success. Newly formed pairs laid eggs later and had slightly smaller clutches than remated pairs. Furthermore, clutch size seemed to increase with successive remating. Overall, our results suggest that newly formed pairs are less efficient in reproduction and that minor yearly reproductive benefits of mate retention might accumulate for birds that are able to breed with the same partner over many years. Because breeding habitat is limited in our study population, Thorn‐tailed Rayaditos could benefit from remating if the number of individuals that can breed exceeds the number of available breeding positions. Profitable long‐term pair bonds might be more frequent in tropical birds and therefore more studies are needed to assess the prevalence of remating‐mediated effects on reproduction in relatively short‐lived monogamous species breeding in tropical regions.