Parent blue-footed boobies suppress siblicidal behavior of offspring

Behaviorally dominant nestlings routinely kill sibling nestmates in blue-fo oted booby (Sula nebouxii) broods during periods of food shortage. Previous work demonstrated that these dominant, first-hatching "A-chicks" regulate the lethality of their behavior towards subordinate, second-hatching "B-chi cks," showing tolerance towards B-chicks except during chronic food shortag es; Siblicide by A-chicks usually occurs after the hatchling stage. Results of an interspecific cross-fostering experiment indicated that A-chicks als o attempt siblicide shortly after hatching, but parents apparently exert co ntrol over these attempts, and thwart them, when chicks are young. Theory p redicts selection for such regulation in siblicidal birds that are likely t o experience genetic parent-offspring conflict over the value of subordinan t nestlings; our evidence of post-hatching parental regulation is consisten t with that prediction.