Shiny Cowbird Parasitism in Central Brazil

Abstract

Recent human settlement in Brasilia, Central Brazil, has greatly reduced the extent of native cerrado vegetation. This has favored the Shiny Cowbird, Molothrus bonariensis, which is common in farmland and certain urban sites. Between September and December of 1982 to 1984, we observed cowbird nestlings (n) or fledglings (f) attended by adults of Mimus saturninus (n), Thraupis sayaca (n), Thraupis palmarum (n,f), Cypsnagra hirundiacea (f), Hemithraupis guira (f), and Ammodramus humeralis (n). The Fork-tailed Flycatcher, Tyrannus savana, is rarely parasitized (one of 87 nests) in Brasilia, perhaps due to the availability of more suitable hosts. In Argentina, this flycatcher is reported to eject cowbird eggs from the nest; we performed artificial parasitism experiments, which suggest hat in Brasilia it might accept cowbird eggs placed during incubation. A new host, the White-banded Tanager (Neothraupis fasciata) was found. It is heavily parasitized in disturbed sites, but virtually unparasitized in native cerrado. Cowbird pressure on cerrado birds is expected to increase with continued fragmentation of this habitat.