When to be your brother’s keeper: Adaptive significance of tolerance to foster siblings in brood parasites

GLOAG, R.; REBOREDA, J.C.; KACELNIK, A.

Perth

Congreso; 13th International Society of Behavioral Ecology Congress; 2010

Young brood parasites share no genetic interest with their hosts’ offspring, yet while many kill nest mates, some avian parasites tolerate and are reared alongside them. Host-tolerance may be adaptive in some circumstances, because host chicks stimulate parental provisioning rates, of which parasites can claim the lion’s share (Kilner et al., 2004, Science 305:877). We build on this ‘beneficial-hosts hypothesis’ in three ways: (1) we model the tradeoff faced by parasites between increased provisioning and increased competition as a function of two aspects of begging: promoting provisioning and disputing food deliveries; (2) We demonstrate that hosts chicks do not benefit a South American host-tolerant, the shiny cowbird, when parasitizing a larger host, as predicted by our model. Cowbirds had 35% greater mortality before fledgling, and at 8 days post-hatch were 23.3% lower in weight when sharing the nest with hosts compared to those raised alone; and (3) we present the first ever video footage of shiny cowbirds parasitizing host nests and puncturing host eggs, and discuss their interactions with hosts during laying in the context of our model, host-tolerance in parasites and the evolution of brood parasitism.