Molothrus ater (Boddaert, 1783)
Table des Planches Enluminéez d'Histoire Naturelle de M. D'Aubenton p.37
The Brown-headed Cowbird (Molothrus ater) is a small brood parasitic icterid of temperate to subtropical North America. They are permanent residents in the southern parts of their range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or April.
They resemble New World orioles in general shape but have a finch-like head and beak. The adult male is mainly iridescent black with a brown head while the adult female is grey with a pale throat and fine streaking on the underparts.
Before European settlement, the Brown-headed Cowbird followed bison herds across the prairies. Their parasitic nesting behaviour complemented this nomadic lifestyle. Their numbers expanded with the clearing of forested areas and the introduction of new grazing animals by settlers across North America. Brown-headed Cowbirds are now commonly seen at suburban birdfeeders.
Unlike the Common Cuckoo, it has no gentes whose eggs imitate those of a particular host.
Host birds sometimes notice the cowbird egg, to which different host species react in different ways. Rejection manifests in three forms: nest desertion (e.g., Blue-gray Gnatcatcher), burying of the egg under nest material (e.g., Yellow Warbler), and physical ejection of the egg from the nest (e.g., Brown Thrasher). Brown-headed cowbird nestlings are also sometimes expelled from the nest.
Some species, such as the House Finch feed their young a vegetarian diet. This is unsuitable for young Brown-headed Cowbirds, meaning almost none survive to fledge.
It seems that Brown-headed Cowbirds periodically check on their eggs and young after they have deposited them. Removal of the parasitic egg may trigger a retaliatory reaction termed "mafia behavior". According to a study by the Florida Museum of Natural History published in 1983, the cowbird returned to ransack the nests of a range of host species 56% of the time when their egg was removed. In addition, the cowbird also destroyed nests in a type of "farming behavior" to force the hosts to build new ones. The cowbirds then laid their eggs in the new nests 85% of the time.
^ a b Henninger (1906)
BirdLife International (2004). Molothrus ater. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 5 May 2006. Database entry includes justification for why this species is of least concern
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