Grayish Baywing

Agelaioides badius

The Birds of the World website identifies the Grayish Baywing with this descriptive information: Traditionally, the Grayish Baywing (Agelaioides badius) has been considered the “primitive,” non-parasitic cowbird and has been known as Molothrus badius. Friedmann’s (1929) view of cowbird taxonomy, and of the evolution of brood parasitism within the icterid blackbirds, had rooted phylogenies of the cowbirds with this species. The Grayish Baywing sometimes is a nest parasite, a behavior considered by Friedmann to be a precursor to brood parasitism. Grayish Baywings, however, incubate their own eggs and rear their own young, often with helpers — and often care for eggs and young of the Screaming Cowbird (Molothrus rufoaxillaris), a brood parasite that almost exclusively parasitizes Grayish Baywings. Friedmann (1929) considered these two species closely related, but this is not the case (Lanyon 1992); regardless of phylogenetic relationships, these two species are tightly bound together in their reproductive biology.

The host-parasitic relationship between Grayish Baywings and Screaming Cowbirds was first realized on 12 April 1873 by W. H. Hudson (1870-1874, 1920) when he collected, from a flock of Grayish Baywings, 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 Grayish Baywing nests must be those of the Screaming Cowbird. Until then, the large numbers of eggs in the nests had generated many questions of their source (e.g., Sternberg 1869). Because these two species show great similarity in-the-nest, information of both species are presented sometimes for comparative purposes in this account.

I saw and photographed a pair of Grayish Baywings on August 29, 2023, at the Pousa Alegre Lodge in the Pantanal of Brazil.  To see my blog that include the sighting of these birds, look here.  Below are a couple of the photographs I took that day.