Mixed mating strategies in cooperatively breeding apostlebirds Struthidea cinerea

Abstract

In cooperatively breeding apostlebirds Struthidea cinerea philopatry by both sexes is coupled with low levels of dispersal, resulting in large groups (up to 17 birds) that may include multiple males and females of varying age and relatedness. We investigated mating patterns within 18 groups of apostlebirds using a set of six polymorphic microsatellite loci. Apostlebirds appear to adopt flexible and context‐dependent mating strategies, with both monogamy and polygamy detected in separate groups. Most groups (11/18, 17/26 group‐seasons) were putatively monogamous, with a single pair matching all typed offspring. Despite the potential for inbreeding, members of breeding pairs were less closely related than other potential within‐group mating combinations. Polygamy was inferred in four groups (four group‐seasons) from the presence of more than four alleles at one locus among offspring within a brood. Pairwise relatedness was lower among adults in polygamous groups than those in groups that included a monogamous breeding pair. There was no conclusive evidence of extra‐group paternity or egg dumping.