About Molothrus rufoaxillaris Cassin, 1866
This species, the screaming cowbird, has mildly iridescent black plumage, with rufous-colored lesser under-wing coverts. Females are slightly duller in color than males. The species has black legs and a reddish brown iris. Adult body length ranges from 18 to 21 cm, with a mean adult weight of 58 g for males and 48 g for females. Its call was first described as "impetuous screaming notes"; for field identification, a more practical description is noisy, explosive, and piercing, and the species also produces rasp-like calls. Screaming cowbirds are most often observed in pairs or small flocks. In South America, the screaming cowbird occurs in northeast and central Argentina, southeast Bolivia, central Brazil, and across all of Paraguay and Uruguay. Its natural habitat is pastureland, where it forages alongside grazing animals such as cows — this habit gives the species the common name "cowbird". Like other cowbirds, it forages primarily on the ground, feeding on invertebrates disturbed by grazing livestock. Due to habitat changes from deforestation and the species following its hosts into new areas, its distribution has grown significantly over recent decades. Both male and female screaming cowbirds have high fidelity to their roosting locations.
