Parent blue-footed boobies suppress siblicidal behavior of offspring

Behaviorally dominant nestlings routinely kill sibling nestmates in blue-footed 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-chicks,” showing tolerance towards B-chicks except during chronic food shortages. Siblicide by A-chicks usually occurs after the hatchling stage. Results of an interspecific cross-fostering experiment indicated that A-chicks also attempt siblicide shortly after hatching, but parents apparently exert control over these attempts, and thwart them, when chicks are young. Theory predicts selection for such regulation in siblicidal birds that are likely to experience genetic parent-offspring conflict over the value of subordinant nestlings; our evidence of post-hatching parental regulation is consistent with that prediction. Received: 6 June 1998 / Accepted after revision: 12 July 1998