Different female shiny cowbird behaviors associated with host characteristics

VANINA D. FIORINI; D. T. TUERO; J. C. REBOREDA

Cornell University, Ithaca, New York, USA.

Congreso; XII International Behavioral Ecology Congress; 2008

International Society for Behavioral Ecology y Cornell University

We analyzed experimentally the effects of the synchronization between parasitism and host laying and the reduction in number of host eggs through egg punctures, on hatching success and chick survival of shiny cowbirds Molothrus bonariensis (45-50 g) in two common hosts that differ in body size: chalk-browed mockingbirds Mimus saturninus (75 g) and house wrens Troglodytes aedon (13 g). We manipulated the synchrony between parasitism and host laying by creating synchronic and asynchronic groups, and the number of host eggs by creating normal and reduced clutches. We did not detect an effect of synchronization of parasitism or number of host eggs removed on cowbird´s hatching success in either host. Survival of cowbird´s chicks was reduced by the extent of hatching synchrony between cowbird and host chicks and by the number of eggs removed in mockingbirds but not in wrens, where cowbird asymptotic weight was higher in nests with normal number of wren chicks than in those with reduced number. We also observed that synchronization of parasitism and number of host eggs punctured per parasitic event were higher in mockingbirds than in wrens. Our results indicate that the main benefit that shiny cowbirds obtain from synchronizing parasitism with host laying and puncturing host eggs is to enhance the survival of their chicks in nests of large hosts. In addition, the differences between hosts in extent of synchronization of parasitism and intensity of egg punctures suggest that shiny cowbirds synchronize their laying and peck host eggs according to host characteristics.