EVIDENCE OF KIN-SELECTED TOLERANCE BY NESTLINGS IN A SIBLICIDAL BIRD

Behaviorally dominant members of blue-footed booby (Sula nebouxii) bro ods can effect siblicide by restricting access of subordinate siblings to parents providing food. In spite of their capacity for siblicide, dominant chicks permit subordinates to feed during short-term food sho rtage; in fact, the proportion of the food that the dominant takes is independent of the total amount delivered in older chicks. A model of optimal food distribution suggests that dominant chicks maximize their inclusive fitness with this pattern, rather than by satisfying their own food requirements and leaving what remains for the subordinate sib ling. The indirect reproductive potential represented by a chick's sib ling appears to have influenced the evolution of siblicidal brood redu ction in this species.