The role of hatching asynchrony in siblicidal brood reduction of two booby species

Abstract

Hatching asynchrony (HA) of masked boobies (Sula dactylatra) in the Galapagos Islands differs from that of its sympatric congener, the blue-footed booby (S. nebouxii), in association with differences in brood reduction systems. Masked booby nestlings are obligately siblicidal, have long HA, and the probability and timing of siblicide is strongly influenced by HA. Blue-footed boobies are facultatively siblicidal and have shorter HA. Experimental shortening of masked booby HA demonstrated that this species maintians its HA above an “early reduction threshold”, below which parents may incur costs of provisioning a brood that they cannot raise to fledging, but that blue-footed booby HA occur above, at, and below the masked booby threshold. Differences in HA alone cannot explain the differences between these two brood reduction systems.