The screaming cowbird (Molothrus rufoaxillaris) is an obligate brood parasite belonging to the family Icteridae and is found in South America.

The distribution of the screaming cowbird has increased significantly in recent decades due to habitat alteration caused by deforestation and by following its hosts into new areas.

[5][8][9][10] In 1874, W H Hudson was first to observe this parasitic relationship when he witnessed what he believed to be baywing chicks morph into screaming cowbird plumage.

[17] Screaming cowbird eggs are spotted like those of their main host, the baywing, but do vary in shape, background colour and markings.

[9] Screaming cowbirds deceive their main host, the baywing, with superb visual chick mimicry.

Although the rearing environment can influence begging call parameters, Screaming Cowbird nestlings develop the acoustic cues required for offspring recognition by the baywings independently of social experience.

[20][30] Chopi blackbirds and brown and yellow marsh birds have not been observed to eject screaming cowbird eggs.

[31] The pre-laying period (the time between nest making and egg laying) of the baywing exhibits great variability in length (1–19 days).

[29] Such behaviours are a fascinating element to the co-evolutionary arms race that exists between avian brood parasites and their hosts.

[21][25][31] Once hatched, baywings treat parasitic chicks as their own, not only by providing food and protection but also by removing ecto-parasites such as botfly larvae.

[2] Reproductive success, as the number of fledgling per egg laid, has been recorded to be 0.14 for the screaming cowbird when hosted by the baywing.