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.