Caregivers in a communally nesting bird do not consistently synchronize nest visits

Abstract

Several hypotheses propose that parent birds might synchronize their visits to the nest, but field studies have historically overlooked the temporal pattern of parental care. Either synchrony or asynchrony could provide adaptive benefits; alternatively, any observed synchrony could simply be a byproduct of other coordinated behavior among caregivers. Few studies have quantified visit synchrony in cooperatively breeding birds with multiple caregivers. We tested whether visits to the nest are more or less synchronized than expected by chance in the communally nesting greater ani (Crotophaga major), a tropical bird that breeds in groups of four to eight adult caregivers. Across 27 breeding groups, anis did not consistently synchronize nest visits more than expected by chance; however, six groups (22%) did exhibit significant synchrony (up to 44% of visits). Nest visit synchrony was not associated with fledging success or brood size, as would be predicted by two common adaptive hypotheses, and instead might be a byproduct of synchronized foraging.

Significance statement

Various hypotheses may explain why birds either synchronize or evenly space their visits to the nest. Such coordination could increase fitness; however, its prevalence and consequences remain poorly understood, particularly in cooperative breeders. We tested whether nest visits were more or less synchronized than expected by chance in a communally nesting bird, the greater ani, which forms breeding groups of four to eight adults. While some breeding groups synchronized nest visits more than expected, most did not. Further, groups with more synchronized visits did not have increased fledging success, suggesting that the synchrony we observed might not provide a fitness benefit but rather could be a byproduct of adult social behavior away from the nest.