Cowbird
| Cowbird | ||||||||||||
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Male Brown-headed Cowbird ( Molothrus ater ) |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Molothrus | ||||||||||||
| Swainson , 1832 |
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The cowbird ( Molothrus ) are a genus of birds in the family of the blackbirds (Icteridae), which occur exclusively in North and South America. This genus includes five species, all of which are brood parasites . Cowbirds were the first species outside of the cuckoo family to be observed to be brood-parasitic.
Way of life
The cowbird are the only birds from America that are breeding parasites . As with the cuckoo , other birds serve as host animals , including vireos and flycatchers . With them, however, the number of host birds is much larger than with the cuckoo. Two of the brut-parasitic cowbirds, namely the giant cowbird and the red-axed cowbird, have specialized in other types of blackbird as host birds. The other three species are generalists and use a wide variety of songbirds as host birds. The number of host birds is unusually high: In North America the brown-headed cowbird, in South America the blackbird or silky-blackbird each use more than 200 host bird species.
The larger eggs are laid individually or in groups by the females in the nests, which contain much smaller eggs, but at least for the giant cowbird and the red-axed cowbird in color similar to the parasitic eggs. The other species often differ greatly from the eggs of the host birds.
The female cowbirds often peck at the host birds' eggs or remove some of the eggs before they lay. The young birds hatch earlier than the brood of the host animals and throw the host brood out of the nest. If the chicks of the host birds survive this crisis and hatch, they are much smaller than the brood of cowbirds and starve to death or are thrown out of the nest. However, many host animals may occasionally raise their own offspring. It is assumed that the cowbirds used to breed themselves.
Often there is no firm bond between the couples. In many species the male reproduces with several females during one breeding period.
They feed on seeds and insects. Often they follow the cows or other grazing cloven-hoofed animals and eat the startled insects.
Discovery of brood parasitism in cowbirds
In 1802, Félix de Azara , one of the most important Spanish South American researchers, stated that the silkwormbird was a parasite in Paraguay and Argentina. He was the first to describe brood parasitism in a species outside of the cuckoo family . Eight years later, Alexander Wilson reported that the brown-headed cowbird does not raise its young itself either. He observed a female of the brown-headed cowbird sitting on the nest of a roach vireo and discovered a little later that there was an egg in the nest that was clearly different from the other eggs in the clutch. In 1861 it was certain that the red-eyed cowbird had its young birds raised by strange parents. The Argentine-British ornithologist William Henry Hudson discovered in 1874 that brood parasitism also applied to the red-axed cowbird. He wrote about his discovery that he would be no less proud of it than if he had discovered a new planet in the sky. In 1894 this behavior was also found in the giant cowbird.
Brood parasitism is not found in any other member of the starling family .
species
- Brown-headed cowbird ( Molothrus ater ( Boddaert , 1783))
- Cowbird ( Molothrus bonariensis ( Gmelin, JF , 1789))
- Rotachsel-Cowbird ( Molothrus rufoaxillaris Cassin , 1866)
- Giant Cowbird ( Molothrus oryzivorus ( Gmelin, JF , 1788))
- Red- eyed cowbird ( Molothrus aeneus ( Wagler , 1829))
The non-parasitic brown cowbird was previously placed in this genus as Molothrus badius ( Vieillot , 1819), but is now assigned to a genus of its own and accordingly referred to as Agelaioides badius . It is often parasitized by the red-axed cowbird.
literature
- NB Davies: Cuckoos, Cowbirds and Other Cheats. T & AD Poyser, London 2000, ISBN 0-85661-135-2 .
