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Brood parasitism

Field site

Field work is conducted in the pampas of the Buenos Aires Province, Argentina in collaboration with Prof. Juan Carlos Reboreda and the Laboratorio de Ecologia y Comportamiento Animal, University of Buenos Aires. The fieldsite is Reserva El Destino (Fundacion Elsa Shaw de Pearson), part-cattle farm and part reserve where biologists are encouraged to live and study the region's various biota. The site supports Shiny Cowbirds ((M. bonariensis) and Screaming Cowbirds (M. rufoaxillaris) and also many host species including Baywing Cowbirds (Agelaioides badius), Chalk-browed mockingbirds (Mimus saturninus) and House Wrens (Troglodytes aedon) and many more. Nests of open-nesting hosts are located by searching the vegetation, while some smaller hosts nest in boxes distributed around the fieldsite. Cowbird parasitism rates can be quite high and multiple parasitism is common in some hosts, such that up to ten cowbird eggs may be laid in a single host nest.

This region of Argentina is also home to many other beautiful birds during the warmer months and the hunt for host nests regularly turns up many other nests and chicks, from hummingbirds to cardinals, not to mention many wonderful critters from other taxa.