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New World bird of the blackbird and oriole (hangnest) family. The male eastern, or common, cowbird is glossy black, about 8 in. (20 cm) long, with a brown head and breast; the female is gray. Most cowbirds lay their eggs in the nests of smaller bird species, victimizing especially vireos, sparrows, and flycatchers. Sometimes the alien egg is ejected or buried under a new nest floor or the nest is abandoned, but usually the host bird incubates the egg and feeds the voracious intruder while its smaller offspring are starved or crowded out. Cowbirds eat seeds but feed chiefly on insects, following behind grazing cattle in order to capture the insects stirred up in this way—hence the name cowbird and the earlier name buffalo bird. Related birds are the bronzed, the California, the dwarf, the Nevada, and the red-eyed cowbirds. Cowbirds are classified in the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, subphylum Vertebrata, class Aves, order Passeriformes, family Icteridae.
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If we were to stop the habitat management program, and likewise if we stopped cowbird control, those threats would immediately start impacting the survival of the species," says Mensing.
Sex ratios and survival probabilities of brown-headed cowbirds (Molothrus ater) in southwest Colorado.
Epigenesis of cowbird song: A Joint endeavor of males and females.
Despite the fact that 97% of cowbird eggs and nestlings do not survive to adulthood, brood parasitism by cowbirds has pushed birds of some host species to the status of "endangered" and has probably hurt populations of birds of some other host species.
Even with parasitic cowbirds, "which are sometimes mistakenly cited as examples of parasites that are not very harmful," he says, hosts nearly always lose all of their young because cowbirds outcompete the host chicks.
Nest parasitism by brown-headed cowbirds represents a threat to the conservation of some bird species (Smith et al.
Critics have waxed lyrical about the numerous images that have remained with them long after the final credits, such as the footage of brown pelicans, who keep a keen eye on dolphins following schools of anchovies, or cowbirds steering clear of bison locking horns, or the bald eagles who let grizzly bears do the hard work in catching salmon before swooping down to steal them.
Sealy and Lorenzana (1997) list several observations of fledged brown-headed cowbirds receiving food from more than one bird species or from a species different from that of the original host.
It also shows how the death of large mammals 20,000 years ago led to the disappearance of one species of cowbird.
cysticola was also detected in one (1/100) free living pigeon in the city of Santiago of Chile (T ORO, 1999) and in one female cowbird (Molothrus ater) with SC lumps on the neck and back (STEWART, 1963).