A model for the evolution of crèching behaviour in gulls

A crèche is an aggregation of chicks outside nesting territories, within chicks continue to be fed only by their own parents. Several adaptive functions of crèching have been proposed, the most frequent being a reduction in predator pressure. Using an evolutionary stable strategy approach based on the computation of individuals' fecundity, we examined which regime of aerial and terrestrial predation is likely to favour the evolution and stability of the crèching strategy (CS) in gulls. Our results confirm the hypothesis that habitat instability associated with high levels of terrestrial predation favours the evolution and maintenance of crèching behaviour. Moreover, our results suggest that a low aggressiveness against predators may be a pre-adaptation to a CS. In contrast, the high synchronisation often observed in crèching species does not favour the evolution of a crèching behaviour and is thus probably under selection pressures different from those modelled here.