Red-crested cardinal defenses against shiny cowbird parasitism: Are aggression towards parasites and egg rejection antagonistic defenses?

SEGURA, LUCIANO N.; REBOREDA, JUAN C.

BEHAVIOUR

BRILL ACADEMIC PUBLISHERS

Año: 2012 p. 325 - 343

0005-7959

Avian brood parasites reduce the reproductive success of the host, which favours evolution of antiparasitic defences, such as aggression towards parasites or rejection of their eggs. It has been proposed that when nest defence is counteracted by parasites, hosts that recognize and reject parasite?s eggs should not defend their nests. The red-crested cardinal, Paroaria coronata, is a potential good-quality host of the shiny cowbird, Molothrus bonariensis. However, the frequency of cowbird parasitism in cardinal nests is very low and there are no records of this host raising parasite?s chicks, which suggest that it may have effective antiparasitic defences. We studied cardinal antiparasitic defences by: 1) presentation of dummy models of a female cowbird and nonpredator and predator control species to nests during laying and incubation, and 2) experiments of artificial parasitism with natural cowbird eggs of different morphs and conspecific eggs during laying and early and late incubation. Our results showed that: 1) frequency of cowbird parasitism in cardinal nests was 7%, 2) cardinals did not exhibit aggressive behaviours towards cowbirds but responded aggressively towards a predator control species, 3) they ejected parasite but not conspecific eggs, 4) there were no costs (breakage or ejection of their own eggs) associated with ejection of parasite?s eggs. Our results are consistent with the hypothesis that aggression towards the parasite and egg rejection are antagonistically expressed. They also indicate that in this host, a relatively low frequency of parasitism is enough selection pressure to maintain egg rejection at a high level.