THE EVOLUTION OF BROOD REDUCTION BY SIBLICIDE IN BIRDS

The young of a number of bird species frequently kill their siblings whilst still in the nest. We develop simple single-locus genetic models of the evolution of siblicide and non-siblicide in bird populations. Two cases are distinguished: (1) where there is an obvious runt which, when siblicide occurs, always perishes and (2) where a siblicidal individual chooses a victim at random from its nest mates. The genetic models are compared with an inclusive fitness analysis of siblicide due to O'Connor (1978, Anim. Behav. 26, 79-96). In the runt model, the genetic analysis and inclusive fitness analysis yield the same results though the genetic analysis reveals a large area of parameter space where both strategies are evolutionarily stable strategies (ESSs) but only one is a continuously stable strategy (CSS). In the model without a runt, the two analyses give different results and for a large area of parameter space both siblicidal and non-siblicidal behaviours are stable to invasion (both ESSs and CSSs) so that the observed state of a population will depend on its past history. © 1990 Academic Press Limited.