Ranging behaviour of brood parasitic Shiny and Screaming Cowbirds while searching for host nests

SCARDAMAGLIA, R.; REBOREDA, J.C.

Chicago

Congreso; Joint meeting of the American Ornithologists' Union and The Cooper Ornithological Society; 2013

AOU-COS

Females of brood parasitic cowbirds lay eggs in nests of other species, the hosts, which provide the totality of parental care. Parasitism occurs at dawn and during the rest of the morning, cowbird females search for nests where to lay eggs on subsequent days. Shiny cowbird (Molothrus bonariensis) females search for nests alone while it has been suggested that females of the screaming cowbird (M. rufoaxillaris) are aided by males. We studied nest-searching behavior in both species at a site in Buenos Aires Province, Argentina. We fitted female and male shiny and screaming cowbirds with 1.2 g radiotransmitters and tracked each individual during 3-6 consecutive days from dawn to dusk. We found considerable overlap between the morning ranges of the same individual in consecutive days. For cowbirds tracked for more than three days, the add of new area to their range decreased over time. There was a marked overlapping in the ranges of male and female screaming cowbirds that were caught together as opposed to those that were caught separately. Our results indicate that shiny and screaming cowbird females use relatively constant areas for nest searching and that female and male screaming cowbirds search for nests together.