Different female shiny cowbird behaviors associated with host characteristics

FIORINI, V.D.; TUERO, D.T.; REBOREDA, J.C.

Cornell University, USA

Congreso; 12th Biennial Congress of the International Behavioral Ecology Society; 2008

Obligate avian brood parasites lay their eggs in nests of other species, which thereafter provide all parental care. Two behaviors that increase the reproductive success of brood parasites are to synchronize parasitism with host laying and to remove or puncture host eggs, but the benefits of these behaviors may depend on hosts characteristics like body size. We experimentally analyzed the effects of synchronization between parasitism and host laying and reduction in number of host eggs on hatching success and chick survival of shiny cowbirds (Molothrus bonariensis) in two common hosts that differ in body mass: chalk-browed mockingbirds Mimus saturninus (75 g) and house wrens Troglodytes aedon (13 g). We did not detect an effect of synchronization of parasitism or number of host eggs removed on parasite hatching success in either host. However, survival of cowbird chicks in mockingbird nests was lower when they hatched after host chicks and when there was no removal of host eggs. In contrast, in wren nests there was no effect of hatching asynchrony and egg removal on cowbird survival, but asymptotic weight was higher in nests without egg removal. In natural nests, the proportion of cowbird eggs laid during host laying was higher and the number of host eggs punctured per parasitic event was greater for mockingbirds that for wrens. These differences between hosts in extent of synchronization between parasitism and host laying and intensity of egg punctures suggest that shiny cowbirds may have adjusted adaptively these behaviors to host characteristics.