Species and sex differences in egg-pecking behavior between parasitic and non-parasitic cowbirds

LLAMBÍAS PAULO E; FERRETTI VALENTINA; REBOREDA, JUAN C.

New Orleans

Congreso; 3rd North American Ornithological Conference; 2002

We compared egg-pecking behavior in males and females of 3 cowbird species: the Shiny Cowbird, Molothrus bonariensis, a host generalist brood parasite, the Screaming Cowbird, M. rufoaxillaris, a host specialist brood parasite, and the Bay-winged Cowbird, M. badius, a non-parasitic species. In experiment 1 we tested if there were species and sexual differences in egg pecking behavior. We offered each bird an artificial nest with 2 plaster eggs and recorded whether the bird pecked and the latency to the first peck. Shiny and Screaming Cowbirds responded in 40.3 and 44% of trials respectively, while Bay-winged Cowbirds did not respond. Females and males of parasitic species showed a similar level of response but Shiny Cowbird males had a lower latency than females. In experiment 2, Shiny Cowbirds faced a choice between a nest with one host egg and a nest with one Shiny Cowbird egg. In experiment 3, Screaming Cowbirds faced a choice between a nest with one Shiny Cowbird egg and a nest with one Screaming Cowbird egg. Shiny Cowbirds pecked preferentially host eggs while Screaming Cowbirds showed a tendency towards pecking Shiny Cowbird eggs. Our results show that egg pecking behavior is present in both sexes and that parasitic cowbirds may discriminate between their own eggs and host or competitor eggs.