Dołączył: 11 Kwi 2011
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|Wysłany: Sob 5:43, 21 Maj 2011
Cowbirds, Molothrus spp. and Scaphidura spp. are parasitic birdsthey arrange their eggs in the nests of other birds (host birds) and let the other species feed and catch on hatchlings.
Some species of birds abandon nests embodying cowbird eggs, or discard the hatchlings, but extra than 150 different species have been inspected to successfully heave youth cowbirds. Cowbird eggs can look very like the eggs of host bird species. Their incubatiin time is short, so the cowbird hatchlings are the first to appear and the 1st to start receiving food from the parent birds. Cowbird chicks, also, can see very alike to host species chicks,[link widoczny dla zalogowanych], by fewest ahead of.
How does a cowbird parasitize a nest?
Evidence suggests that many species are no harmed by cowbird parasitism. Host young may do equally well, or even better, sharing a nest with cowbird chicks than they would in an unparasitized nest. Many species have the opportunity to nest again in the same season and bring their numbers of descendant up.
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Are host species harmed by cowbirds?
Brown-headed Cowbirds often lay eggs in meadowlark nests.
The female cowbird watches and waits until the host bird begins laying. Then she pays a fast visit to the host nest, lays an egg and leaves. Four or five eggs may be laid in the same host nest, merged in with the hosts grasp. In some cases, cowbirds remove host eggs from the nest to make apartment for their own.
Overall, Brown-headed Cowbirds, favor numerous additional North American birds, are declining. Control programs, remedying them as pest birds and using deadly measures to reduce mathematics have been forcible, but only locallythese amounts only seem logical where host species are threatened.
Why do other birds raise cowbird young?
One cause host birds put up with cowbird young may be panic of reprisals: 1 study showed that in nests where cowbird eggs were removed, there was a higher rate of vandalismpresumably by irate cowbird parentsthan in nests where the host birds incubated cowbird eggs and raised cowbird young. Although host nestlings underwent from having to compete for food with the larger cowbird nestlings, they did better overall than those in non-parasitized nests.
Screaming Cowbirds and Giant Cowbirds usually parasitize the nests of closely narrated speciesthe Brown-headed Cowbird, very prevalent in North America, and the Shiny Cowbird ambition lay eggs in the nests of hundreds of different species. Some Brown-headed Cowbirds evidently specialize in parasitizing particular host species.
In some districts, 90 percentage of a given host species nests may be parasitized along cowbirds; although, this usually merely occurs locally. When a bird has a restricted propagating range and namely heavily parasitized by cowbirds, there is a adverse effect aboard the host population. For instance, the Kirtlands Warbler and Black-capped Vireo have both been heavily impacted by Brown-headed Cowbirds.
Recent testify suggests that if a feminine Brown-headed Cowbird misses the window of opportunity and discovers a host lair afterward eggs have yet been laid, she may vandalize the nest, forcing the host bird to begin over. This would give the cowbird a second become apt parasitize that birds nest.
Cowbirds scan as nests in which to lay their eggs. They tend to quest approximate their foraging areasin agricultural areas where there are abundant seeds,[link widoczny dla zalogowanych], urban areas,[link widoczny dla zalogowanych], and grasslands bordering forests. Thus, host species' nests in these areas are parasitized more often than nests in other habitats.
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