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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.
The brown-headed cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors. [14] [15] More than 140 different species of birds are known to have raised young cowbirds. [16] The young cowbird is fed by the host parents at the expense of their own young.
Female hooded orioles lay a clutch of 3–5 eggs. The eggs are generally white, but can range into a pale blue with darker splotches. The eggs are incubated for 12–14 days, and the nestlings take about 14 days to fledge. This species is also commonly parasitized by the brown-headed cowbird and the bronzed cowbird. [9]
The screaming cowbird is a specialist brood parasite, predominantly parasitizing the nests of baywings (Agelaioides). [5] [8] [9] [10] In 1874, W H Hudson was first to observe this parasitic relationship when he witnessed what he believed to be baywing chicks morph into screaming cowbird plumage.
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.
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 ...
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.
Without human intervention, the warblers are severely impacted by nest parasitism by the brown-headed cowbird. Blue jays prey on the nests and are a nuisance species because individual jays repeatedly allow themselves to get caught in the same traps used to exterminate the cowbirds of the nesting region. [30]