Non-linear Influence of Nest Size on Thermal Buffering of Sociable Weaver Nests and the Maintenance of Cooperative Nest Construction

Abstract

Communal nests often provide benefits, such as protection from predators and refuge from extreme temperatures, to the inhabitants of the nest. The benefits returned to individuals performing nest construction may not scale linearly with the amount of nest construction performed. If the returns on nest construction are non-linear, then recent theoretical studies suggest that selection for reproductive competition may destabilise the cooperative behaviours that maintain the communal nest. To investigate these questions, we measured the thermal benefits provided by sociable weaver (Philetairus socius) nests, and how those benefits scale at multiple nest sizes, including the point where zero investment in nest building returns no benefits. We find that the average temperature buffering provided by nest chambers is correlated with distance to the edge of the nest and that the benefits provided by nest construction are asymptotic. This suggests that cooperative nest construction will maintained at a lower level than if the benefits were linear.