Parental incubation patterns and the effect of group size in a Neotropical cooperative breeder

Abstract

ABSTRACT In many cooperatively breeding species, young (“helpers”) from one year help other adults raise offspring the following year. In contrast to helper effects during the nestling or postfledging stages of the avian breeding cycle, potential benefits from helpers during incubation are poorly studied. We analyzed 39 clutches and recorded 6,027 off-bouts to document incubation behavior in the White-breasted Thrasher (Ramphocinclus brachyurus), an endangered Neotropical facultative cooperative breeder. Our goal was to test the prediction that cooperation confers benefits during incubation in terms of increased nest attendance and hatching success. We found that 65% of active hours (0500–2100) are spent on the nest, values somewhat lower than average for a tropical passerine with uniparental incubation. Highest incubation constancy was observed at a rare 4-egg clutch, which was attended by putative joint-nesters. Excluding this clutch, differences in incubation behavior between pair and cooperative group...