Sociality beyond helpers at the nest: the number of strong associations predict reproductive trade-offs in a cooperative breeder

Gabriel Munar-Delgado, Liliana Silva, André Ferreira, Claire Doutrelant, Rita Covas

Individual social relationships can shape fitness across taxa, but in studies on cooperatively breeding species, the social environment relevant to reproduction is typically reduced to the number of helpers. We tested whether breeder sociality beyond helper number predicts reproductive performance in a colonial cooperative bird, the sociable weaver (Philetairus socius). Using long-term data and social networks built from foraging associations, we quantified individual sociality as the relative number of strong social bonds each individual maintained within its colony. We then tested whether this measure of sociality predicted multiple reproductive outcomes while accounting for helper number. Breeder sociality was unrelated to helper number, and its associations with reproductive performance differed between the sexes. While we found no evidence that sociality predicted breeding timing within the season, there was a tendency for chicks raised by high-sociality mothers to show higher fledging success. In breeding males, offspring of medium- and high-sociality fathers were heavier than those of low-sociality fathers. However, high-sociality males also initiated reproduction later in life than low-sociality males. These results show that cooperative breeding is embedded within multi-layered social structures beyond helper number, and that individual sociality may be linked to sex-specific life-history trade-offs.