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The brown-headed cowbird is an obligate brood parasite; it lays its eggs in the nests of other small passerines (perching birds), particularly those that build cup-like nests. The brown-headed cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors.
The female cowbird notes when a potential host bird lays its eggs, and when the nest is left momentarily unattended, the cowbird lays its own egg in it. The female cowbird may continue to observe this nest after laying eggs. Some bird species have evolved the ability to detect such parasitic eggs, and may reject them by pushing them out of ...
Different host species show different responses to their nests being parasitised, with behaviours ranging from accepting and caring for the cowbird eggs, to rejecting the eggs from the nest. [2] As the shiny cowbird is an effective generalist brood parasite, it can be considered the South American counterpart to the brown-headed cowbird. [6]
The screaming cowbird frequently parasitizes its main host, the baywing, during the pre-laying period. [20] Screaming cowbirds lay 31% of their eggs before the first baywing egg but most of the eggs laid are ejected, and often within 24 hours. [29] By ejecting parasitic eggs with their feet, baywings can reduce the parasitic egg load by 75%. [30]
A shiny cowbird chick (left) being fed by a rufous-collared sparrow Eastern phoebe nest with one brown-headed cowbird egg (at bottom left) Shiny cowbird parasiting masked water tyrant in Brazil. Brood parasitism is a subclass of parasitism and phenomenon and behavioural pattern of animals that rely on others to raise their young.
The American robin rejects cowbird eggs, so brood parasitism by the brown-headed cowbird is rare, and the parasite's chick does not often survive to fledging. [41] In a study of 105 juvenile robins, 77.1% were infected with endoparasites, Syngamus sp. being the most commonly encountered, in 57.1% of the birds. [42]
[3] [17] Cowbird parasitism peaks in April at 41%, and is as low as 8% and 0% in July and August, respectively. Female cowbirds sometimes eject Carolina wren eggs before laying their own, and even if host eggs are retained, the size of cowbird eggs negatively affect the hatching success of wren eggs.
The giant cowbird (Molothrus oryzivorus) is a large passerine bird in the New World family Icteridae. It breeds from southern Mexico south to northern Argentina, and on Trinidad and Tobago. It may have relatively recently colonised the latter island. It is a brood parasite and lays its eggs in the nests of other birds.