Does Booby Egg Dumping Amount to Quasi‐Parasitism?

Quasi‐parasitism occurs when a paired male facilitates dumping in its own nest by an extra‐pair female with which it has recently copulated. Although numerous observations hint at quasi‐parasitism in diverse avian species, direct behavioral confirmation of male complicity is required to exclude the alternative adaptive explanations enumerated by Griffith et al. Behav. Ecol. Sociobiol. 56 (2004) 191]. Our direct observations on dumping by female blue‐footed boobies (Sula nebouxii) show apparent male ambivalence: males were hostile to eggs dumped by their extra‐pair partners but half‐hearted in repelling those partners after the act of dumping. Hostility was evidenced when a host male that was present during dumping destroyed the extra‐pair partner's egg and when extra‐pair partners selectively dumped when the host male was absent or distracted rather than when it was alone on the territory. Host males appear to deter dumping by their extra‐pair partners rather than facilitating it, and their partial tolerance of females that have dumped may be a result of their general tolerance of unaccompanied females. Although paired male boobies sometimes copulate with females that dump into their nests, apparently this is not quasi‐parasitism.