In environmental toxicity testing, the use of native species is normally recommended as it provides greater environmental realism and insures a more conservative endpoint for protecting ecosystems. Although pesticide products are vastly used in South American agriculture, no test protocols or guidelines exist for testing effects on native or indigenous bird species. Instead, recommended test species and guidelines are essentially the same as those developed for Europe and North America. At the same time, avian pesticide regulatory assessment in South America does not require testing on passerine species, even though Passeriformes are normally more sensitive than other groups of birds and represent approximately 60% of all living species of bird. The aim of this chapter is to propose South American cowbirds as candidate passerine avian models for environmental toxicity testing in South American countries. Three species of cowbirds are widely distributed in South America and can be considered potential avian model for environmental toxicity testing: the shiny cowbird (Molothrus Bonariensis), the screaming cowbird (Molothrus rufoaxillaris) and the bay-winged cowbird (Ageloides badius). This chapters briefly reviews and compares avian environmental toxicity testing in South America and the rest of the world, and describes requirements for maintaining cowbirds in captivity and using them in toxicity testing.