Experimental evidence for an antipredatory function of egg rejection behaviour in a common host of the brood-parasitic shiny cowbird

DE MÁRSICO, M.C.; URSINO, C.A.; REBOREDA, J.C.

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY

SPRINGER

Lugar: Berlin; Año: 2016 vol. 70 p. 1689 - 1697

0340-5443

The rejection of foreign eggs is the most effective adaptation against brood parasitism in birds. Many hosts, however, show suboptimal responses towards parasitic eggs, which could reflect a compromise between the benefits and costs of egg rejection. Some large-sized hosts of the shiny cowbird (Molothrus bonariensis) accept any spotted parasite egg but reject a rarer pure white egg morph that occurs only in some parts of the parasite?s distribution. This behaviour is intriguing because it is not an effective defense against parasitism and recent evidences suggest that large-sized hosts could benefit from accepting cowbird eggs as this may dilute the risk of host egg losses at multiply parasitized nests. We studied whether rejection of pure white cowbird eggs can be driven by the increased predation risk of host nests parasitized with this conspicuous egg morph. We conducted a nest predation experiment using artificial clutches placed in natural, inactive nests of a large-sized host, the chalk-browed mockingbird (Mimus saturninus). Clutches consisted of two eggs resembling either one host plus one pure white cowbird egg, one host plus one spotted cowbird egg, or two host eggs. Clutches with pure white eggs were more likely to be predated than those having either two host eggs or one host and one spotted cowbird egg, supporting an antipredatory function of egg rejection behaviour in mockingbirds. These results suggest that nest predation could operate as part of larger fitness trade-offs shaping host responses towards foreign eggs. Considering the role of nest predation in the studies of host rejection decisions would help to better understand the evolution and expression of antiparasite defenses, especially when hosts seem to behave suboptimally against costly brood parasitism.