Brood parasitic shiny and screaming cowbirds prospect suitable nests before laying their eggs

SCARDAMAGLIA R; FIORINI VD; KACELNIK A; REBOREDA JC

New York

Congreso; 15th Conference of the International Society of Behavioral Ecology; 2014

International Society of Behavioral Ecology

Females of brood parasitic shiny (Molothrus bonariensis) and screaming (M. rufoaxillaris) cowbirds parasitize host nests just before sunrise. Previous studies showed that females of these species know the location of the nests where they lay their eggs beforehand, since they fly directly from the roost to the nest at dawn. After laying, they would use the rest of the morning to search for nests to parasitize in subsequent days. We tested the hypothesis that female cowbirds prospect nests, i.e. they search for and detect nests that are at a suitable stage to parasitize the following days. We fitted females with coded radio-tags and monitored the nests of the main hosts (chalked-browed mocking birds for shiny cowbirds and baywings for screaming cowbirds) during the pre-laying, laying and early incubation periods using coded proximity data-loggers. We recorded 6 parasitic events by tagged shiny cowbirds and 11 by tagged screaming cowbirds. All the parasitic events were preceded by at least one visit of the female to the nest during the previous days. The visit rate prior to the parasitic event was 1.00 ± 0.23 (mean ± SE) visits per day for shiny and 2.36 ± 0.85 visits per day for screaming cowbirds. We found two cases of repeat parasitism, i.e. a female laying two eggs in the same host nest, in screaming cowbirds but none in shiny cowbirds. Our results show that female shiny and screaming cowbirds prospect suitable hosts? nests before returning to them to lay their eggs.