The Giant Cowbird

Not a Corvid!

Last month we brought you a delightful and silly un-corvid, the Willy Wagtail. This month is a much more sinister subject – the Giant Cowbird (Molothrus oryzivorus).

By Peter VanZoest

The Cowbird one of the few entirely black birds found in Central and South America. It is a quiet bird, particularly for an icterid, but the male has an unpleasant screeched whistle, shweeaa-tpic-tpic. The call is a sharp chek-chik.  Like corvids, they are also very adept mimics.

What sets the birds apart from Crows and Ravens in their behavior is that they are brood parasites, laying eggs in the nests of oropendolas and caciques in the same way Cukoos lay eggs in Crow nests. The eggs are of two types, either whitish and unspotted, or pale blue or green with dark spots and blotches. The host’s eggs and chicks are not destroyed, but there is considerable doubt about the theory that the young Giant Cowbirds benefit the host’s chick by removing and eating parasitic flies. In some cases it has been observed that the cowbird chick will push the others out.

Also like Crows and Jackdaws, the Giant Cowbird is large at 36-40 cm (14 in) long, weighs 180 g (6.3 oz) and is iridescent black, with a long tail, long bill, small head, and a neck ruff which is expanded in display. The female is smaller, averaging 28 cm (11 in) long and weighing 135 g (4.8 oz). She is less iridescent than the male, and the absence of the neck ruff makes her look less small-headed. Juvenile males are similar to the adult male, but browner, and with a pale bill. You can easily tell them apart from crows by noting the beady yellow eye, as well as the tiny skull.

By Tom Davis