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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.
Although Carolina wrens are fairly common, brood parasitism by the brown-headed cowbird is common, with up to 25% of Carolina wren nests being affected in certain regions such as Oklahoma and Alabama. [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 ...
The brown-headed cowbird, a brood parasite, will lay its eggs in house finch nests, although the diet house finches feed their young is inadequate for the young cowbirds, which rarely survive. [ 26 ] In 2012, house finches positive for West Nile virus were found in northwestern Riverside County , CA.
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 their nests, but the female cowbird has been observed to attack and destroy the remaining eggs of such birds as a consequence, dissuading further removals.
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.
One study found that 9% of nests had brown-headed cowbird eggs in them. [32] It likely evades parasitism partly because of its late breeding season. [33] The American goldfinch also makes a very poor host for brood parasites, with studies showing low hatching rates of brown-headed cowbird eggs and no fledging success.
After the eggs have been laid, both males and females cover “nest duty,” where the eggs will incubate for an average of 21 days, continued the National Audubon Society. The White Ibis.
In a South Carolina old field, 5 of 19 eastern towhee nests were parasitized. [51] Each parasitized nest contained 1 Brown-headed Cowbird egg. The desertion rate for parasitized nests was 20%, which was similar to nests that had not been parasitized (21%). Two of the five Brown-headed Cowbird eggs produced fledglings.