Breeding experience and pair bond duration both increase reproductive success in an avian cooperative breeder

Abstract

Monogamous mating systems occur across many animal taxa and are especially prevalent in birds. In species with long-term monogamy, individuals may remain with the same breeding partner or switch partners from year to year. Longer pair bonds may reduce costly mate sampling, increase familiarity and coordination within pairs and help defend territories across years, suggesting pathways to more success in long-lasting pairs such as increased reproductive success and greater breeder survival. One challenge in the study of long-term monogamy remains to disentangle the effects of age, breeding experience and pair bond duration on survival and reproductive success, as all three can act independently in determining whether long-lasting pairs are more successful. We investigated the effect of pair bond duration and breeding experience in the Florida scrub-jay, Aphelocoma coerulescens, a cooperative breeder, using longitudinal and cross-sectional approaches taking advantage of frequent re-pairing in older individuals induced by partner's death or divorce. Based on 35 years of observations, we found that both breeding experience and pair bond duration independently increased reproductive success (number of nutritionally independent young), controlling for age and other drivers of reproductive success including territory size, population density, food availability and group composition. Neither breeding experience nor pair bond duration influenced the odds of surviving the nonbreeding season for breeders and juveniles, but the odds of surviving the breeding season slightly increased for experienced breeders. We also found that mating with an older partner reduced survival in the nonbreeding season. Therefore, mate switching appears to be costly if individuals re-pair with an inexperienced partner or an older one. This study highlights the importance of experience in determining reproductive success especially when experience is acquired with the same partner over the years.