Maternal allocation in relation to weather, predation, and social factors in a colonial cooperative bird

Females may adjust prenatal allocation in relation to ecological conditions that affect reproductive success, such as weather conditions or predation risk. In cooperative breeders, helpers might also influence reproductive success and previous studies suggest that females can lay smaller eggs or larger clutches when breeding with more helpers. Although recent work suggests that helper effects can vary according to climatic variables, how social and ecological factors interact to shape prenatal allocation is poorly understood.

Here, we examine how ecological and social components of the breeding environment co-vary with egg mass and clutch size, using as a model the sociable weaver (Philetairus socius), a colonial, cooperatively breeding passerine. The study spanned 9 years and included over 1900 eggs from over 550 clutches. Our analyses combined natural variation in weather conditions (rainfall before each reproductive event) with a nest predator-exclusion experiment and continuous m...