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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 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 shiny cowbird's diet consists mainly of insects, other arthropods [4] and seeds, and they have been recorded foraging for grains in cattle troughs. [2] Like most other cowbirds, it is an obligate brood parasite, laying its eggs in the nests of many other bird species such as the rufous-collared sparrow. [5]
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.
English: Brood parasitism by cowbirds can sometimes include multiple cowbird eggs. In this nest, only one of the host eggs remains (smaller egg with distinct band of reddish-brown streaks), the rest belonging to brown-headed cowbirds
The host's eggs and chicks are not destroyed. Their icterid hosts breed colonially, and defend their nests vigorously, so even a large, bold and aggressive species like the giant cowbird has to cover an extensive territory to find sufficient egg-laying opportunities. Several giant cowbird eggs may be laid in one host nest.
Song sparrows' nests are parasitized by the brown-headed cowbird. The cowbirds' eggs closely resemble song sparrows' eggs, although the cowbirds' eggs are slightly larger. Song sparrows recognize cowbirds as a threat and attack the cowbirds when they are near the nest. There is some evidence that this behavior is learned rather than instinctual ...