Screaming Cowbird

The Screaming Cowbird, known scientifically as Molothrus rufoaxillaris, is a bird cloaked in mildly iridescent black plumage, with the lesser under-wing coverts displaying a rufous hue. The males are slightly more vibrant than the females. These birds possess black legs and a reddish-brown iris, with adults measuring between 18 to 21 centimetres in length. Males typically weigh around 58 grams, while females are lighter at approximately 48 grams.

Identification Tips

When attempting to identify the Screaming Cowbird, look for its noisy, explosive, and piercing calls, which may also include a rasp-like quality. These birds are often observed in pairs or small flocks, and their distinctive vocalizations can be a reliable indicator of their presence.

Habitat

The Screaming Cowbird is a denizen of pasturelands, often seen foraging among grazing animals such as cows, which is the origin of its common name.

Distribution

This species is native to South America, with its range encompassing northeast and central Argentina, southeast Bolivia, central Brazil, and throughout Paraguay and Uruguay. The Screaming Cowbird's distribution has expanded in recent decades due to habitat changes from deforestation and by following its hosts into new areas.

Behaviour

Screaming Cowbirds exhibit high fidelity to their roosting locations. They are monogamous, forming stable pairs throughout the breeding season.

Song & Calls

The Screaming Cowbird's vocalizations were initially described as "impetuous screaming notes." For field identification, listen for their characteristic noisy and explosive calls, which may also include a rasp-like sound.

Breeding

The Screaming Cowbird is a specialist brood parasite, mainly targeting the nests of baywings (Agelaioides). It has also been known to parasitize the nests of the chopi blackbird (Gnorimopsar chopi) and the brown-and-yellow marshbird (Pseudoleistes virescens), especially in areas where baywings are absent. Screaming Cowbirds lay eggs that are spotted similarly to those of their main host, the baywing, although there can be variations in shape, background colour, and markings. They can lay multiple eggs in a single baywing nest, with up to 12 females parasitizing the same nest. Adults of this species have been observed piercing the eggs of their hosts and other parasite eggs, possibly to reduce competition and enhance the survival of their offspring.

Diet and Feeding

Screaming Cowbirds forage predominantly on the ground, consuming invertebrates that have been disturbed by grazing animals.

Conservation Status

The Screaming Cowbird is currently listed as Least Concern on the IUCN Red List, indicating that it is not at immediate risk of population decline or extinction.