Screaming Cowbird

Molothrus rufoaxillaris

The Birds of the World website introduces the Screaming Cowbird with this descriptive information:  The Screaming Cowbird is a specialist brood parasite, parasitizing almost exclusively the Bay-winged Cowbird (Agelaioides badius). This host-parasitic relationship was first realized on 12 April 1873 by W. H. Hudson (1874, 1920) when he collected, from a flock of Bay-winged Cowbirds, young Screaming Cowbirds, which were molting from their “Bay-winged” juvenile plumage to the “Screaming Cowbird” adult plumage. Hudson then understood that the “extra” eggs in Bay-winged Cowbird nests must be those of the Screaming Cowbird — “the eggs of the two species are identical in form, size, and coloration, and that, stranger still, the mimicry is as perfect in the young birds as in the eggs” (Hudson 1874: 162; see also Hudson 1920: 104). Because of this in-the-nest similarity, information of both species are presented for comparative purposes in some sections of this account. 

I met my first Screaming Cowbird on Thursday morning, August 31, 2023.  Our Jeff Parker Tour group was staying at Southwild’s Pouso Alegre Lodge and on this morning I was hanging out at the main feeder at the Lodge.  Our guide Liko was kind enough to explain to me the three types of Cowbirds in terms of their size.  The Screaming Cowbird is the smallest, the Shiny Cowbird is in the middle, and the Giant Cowbird is by far the largest.  For details of my Brazilian trip that include the sighting of this bird, look here.  Below are a couple of my photos of this bird. In each of the photos, the Screaming Cowbird is the smaller black bird on the left.