Cowbirds are birds belonging to the genus Molothrus in the family Icteridae. They are of New World origin. They are brood parasites, laying their eggs in the nests of other species.

The genus Molothrus contains:

Image Scientific name Common Name Distribution
Screaming Cowbird (Molothrus rufoaxillaris) Molothrus rufoaxillaris Screaming cowbird north east and central Argentina, south east Bolivia, central Brazil and throughout Paraguay and Uruguay
Giant Cowbird - Pantanal - Brazil H8O0545 (23593619780) Molothrus oryzivorus (formerly in Scaphidura) Giant cowbird southern Mexico south to northern Argentina, and on Trinidad and Tobago
Bronzed Cowbird (Molothrus aeneus) (7223072934) Molothrus aeneus Bronzed cowbird southern U.S. states of California, Arizona, New Mexico, Texas, and Louisiana south through Central America to Panama
Shiny cowbird (Molothrus bonariensis) male Molothrus bonariensis Shiny cowbird South America
Molothrus ater 2 Molothrus ater Brown-headed cowbird Soutwestern Canada, United States and Mexico

The non-brood parasitic baywing was formerly placed in this genus; it is now classified as Agelaioides badius.

Molothrus ater1
Female brown-headed cowbird
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Icteridae
Genus: Molothrus
Swainson, 1832


Cowbirds eat insects, including the large numbers that may be stirred up by cattle. In order for the birds to remain mobile and stay with the herd, they have adapted by laying their eggs in other birds' nests. The cowbird will watch for when its host lays eggs, and when the nest is left unattended, the female will come in and lay its own eggs. The female cowbird may continue to observe the nest after laying eggs. If the cowbird egg is removed, the female cowbird may destroy the host's eggs to dissuade further removals, according to the Mafia hypothesis.[1]


  1. ^ Jeffrey P. Hoover; Scott K. Robinson (13 March 2007). "Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs". Proceedings of the National Academy of Sciences. Retrieved 26 August 2009.
  • Jaramillo and Burke, New World Blackbirds ISBN 0-7136-4333-1

External links


The baywings are two species of birds in the genus Agelaioides, which were described in the early 19th century. These species are found in Brazil and in the case of A. badius, also Argentina, Bolivia, Uruguay, and Paraguay. They were formerly in included in genus Molothrus with cowbirds.

Bell's vireo

Bell's vireo (Vireo bellii) is a small North American songbird. It is 4.75 to 5 in (12.1 to 12.7 cm) in length, dull olive-gray above and whitish below. It has a faint white eye ring and faint wing bars.

This bird was named by Audubon for John Graham Bell, who accompanied him on his trip up the Missouri River in the 1840s.

The least Bell's vireo (Vireo bellii pusillus), is an endangered subspecies in Southern California. Consideration of Bell's vireo has been a factor in several land development projects, to protect least Bell's vireo habitat. The decline of the least Bell's vireo is mostly due to a loss of riparian habitat and brood parasitism by the brown-headed cowbird (Molothrus ater).

Black-whiskered vireo

The black-whiskered vireo (Vireo altiloquus) is a small passerine bird, which breeds in southern Florida, USA, and the West Indies as far south as the offshore islands of Venezuela. It is a partial migrant, with northern birds wintering from the Greater Antilles to northern South America. This species has occurred as a rare vagrant to Costa Rica.

The breeding habitat is open deciduous wooded areas and cultivation, and in Florida also mangroves. The black-whiskered vireo builds a cup nest in a fork of a tree branch, and lays 2-3 white eggs.

This vireo is 14–15 cm in length, has a 25 cm wingspan and weighs 17–19 g. It has thick blue-grey legs and a stout bill.

The adult black-whiskered vireo has dull olive-green upperparts and white underparts, with yellowish on the flanks and under the tail. It has red eyes and a grey-brown crown with faint dusky edges. There is a dark line through the eyes and a white eyebrow stripe. There is a distinctive black line (the “whisker”) on the neck sides. Juvenile birds are similar, but have brown-red eyes.

This species is similar to red-eyed vireo, but is duller and browner above, and is best distinguished by the black whisker mark. The song is a three-syllable whip, Tom Kelly, more abrupt than that of red-eyed vireo.

The Florida race V. a. barbatulus is shorter-billed by 15% than the northern Caribbean subspecies V. a. bonairensis. The latter form has occurred in the USA as a vagrant to Florida and Louisiana.

The black-whiskered vireo gleans insects from tree foliage, sometimes hovering while foraging. It will also eat small quantities of berries

This bird suffers from nest parasitism by the brown-headed cowbird in its US range, and shiny cowbird further south.

Bran-colored flycatcher

The bran-colored flycatcher (Myiophobus fasciatus) is a small passerine bird in the tyrant flycatcher family. It breeds from Costa Rica through South America to Bolivia, Uruguay, and Argentina. It also occurs on Trinidad.

This species is found in open forests and secondary growth. The deep cup nest is made of stems and bark and lined with fine plant fibers; it is suspended by the rim from a side branch low in a tree. The typical clutch is two cream-colored eggs with a rufous wreath. The female incubates for 17 days with a further 15–17 to fledging. This species is parasitized by the shiny cowbird.

The adult bran-colored flycatcher is 12.7 cm long and weighs 10.5g. The head and upperparts are dark reddish brown and the crown has a concealed yellow crest, which is erected by excited adults. There are two pale buff wing bars and the underparts are whitish shading to pale yellow on the belly and with dark streaking on the breast and flanks. The bill is black above and brown below. Sexes are similar, but young birds lack the crown patch.

Bran-colored flycatcher are solitary unobtrusive birds, sometimes difficult to see as they move rapidly through the undergrowth in search of small insects and berries. They have a whistled chep, chewee call.

Bronzed cowbird

The bronzed cowbird (once known as the red-eyed cowbird), (Molothrus aeneus), is a small icterid.

It breeds from the southern U.S. states of California, Arizona, New Mexico, Texas, and Louisiana south through Central America to Panama. They tend to be found in farmland, brush, and feedlots. Outside the breeding season, they are found in very open habitats, and roost in thick woods. They forage in open areas, often nearby cattle in pastures. Their diet mostly consists of seeds and insects, along with snails during breeding season for a calcium source.

There are three subspecies and an isolated population on the Caribbean coast of Colombia that is sometimes treated as a separate species, the bronze-brown cowbird (M. armenti):

M. a. loyei – Parkes & Blake, 1965: found in the southwestern United States and northwestern Mexico

M. a. assimilis – (Nelson, 1900): found in southwestern Mexico

M. a. aeneus – (Wagler, 1829): nominate, found in southern Texas (south central USA) and from eastern Mexico to central PanamaThe male bronzed cowbird is 20 cm (7.9 in) long and weighs 68 g (2.4 oz), with green-bronze glossed black plumage. Their eyes are red in breeding season and brown otherwise. The female is 18.5 cm (7.3 in) long and weighs 56 g (2.0 oz). She is a dull black with a brown underbelly, and has brown eyes. Young birds have coloring similar to the females, with the exception of grey feather fringes.Like all cowbirds, this bird is an obligate brood parasite; it lays its eggs in the nests of other birds. The young cowbird is fed by the host parents at the expense of their own young. Hosts include Prevost's ground-sparrow and White-naped brush finch. They develop rapidly, leaving the nest after 10–12 days.

Brood parasite

Brood parasites are organisms that rely on others to raise their young. The strategy appears among birds, insects and some fish. The brood parasite manipulates a host, either of the same or of another species, to raise its young as if it were its own, using brood mimicry, for example by having eggs that resemble the host's (egg mimicry).

Brood parasitism relieves the parasitic parents from the investment of rearing young or building nests for the young, enabling them to spend more time on other activities such as foraging and producing further offspring. Bird parasite species mitigate the risk of egg loss by distributing eggs amongst a number of different hosts. As this behaviour damages the host, it often results in an evolutionary arms race between parasite and host as the pair of species coevolve.

Brown-headed cowbird

The brown-headed cowbird (Molothrus ater) is a small obligate brood parasitic icterid of temperate native to subtropical North America. They are permanent residents in the southern parts of their range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or April.

Eastern phoebe

The eastern phoebe (Sayornis phoebe) is a small passerine bird. The genus name Sayornis is constructed from the specific part of Charles Lucien Bonaparte's name for Say's phoebe, Muscicapa saya, and Ancient Greek ornis, "bird". Phoebe is an alternative name for the Roman moon-goddess Diana, but it may also have been chosen to imitate the bird's call.This tyrant flycatcher breeds in eastern North America, although its normal range does not include the southeastern coastal United States.

It is migratory, wintering in the southernmost United States and Central America. It is a very rare vagrant to western Europe. This is one of the first birds to return to the breeding grounds in spring and one of the last to leave in the fall. They arrive for breeding in mid-late March, but they return to winter quarters around the same time when other migrant songbirds do, in September and early October; migration times have stayed the same in the last 100 years. The increase in trees throughout the Great Plains during the past century due to fire suppression and tree planting facilitated a western range expansion of the eastern phoebe as well as range expansions of many other species of birds.This species appears remarkably big-headed, especially if it puffs up the small crest. Its plumage is gray-brown above. It has a white throat, dirty gray breast and buffish underparts which become whiter during the breeding season. Two indistinct buff bars are present on each wing. Its lack of an eye ring and wingbars, and its all dark bill distinguish it from other North American tyrant flycatchers, and it pumps its tail up and down like other phoebes when perching on a branch. The eastern phoebe's call is a sharp chip, and the song, from which it gets its name, is fee-bee.

The eastern wood pewee (Contopus virens) is extremely similar in appearance. It lacks the buff hue usually present on the lighter parts of the eastern phoebe's plumage, and thus has always clearly defined and contrasting wing-bars. It also does not bob its tail habitually, and appears on the breeding grounds much later though it leaves for winter quarters at about the same time as the eastern phoebe.The breeding habitat of the eastern phoebe is open woodland, farmland and suburbs, often near water. This phoebe is insectivorous, and often perches conspicuously when seeking food items. It also eats fruits and berries in cooler weather.

It often nests on human structures such as bridges and buildings. Nesting activity may start as early as the first days of April. The nest is an open cup with a mud base and lined with moss and grass, built in crevice in a rock or man-made site; two to six eggs are laid. Both parents feed the young and usually raise two broods per year. The eastern phoebe is occasionally host to the nest-parasitic brown-headed cowbird (Molothrus ater).

Five-striped sparrow

The five-striped sparrow (Amphispiza quinquestriata) is a medium-sized sparrow.

This passerine bird is primarily found along the eastern Gulf of California region and Pacific region of mainland western Mexico, with a breeding range that extends into the southern tip of the U.S. state of Arizona, the Sierra Madre Occidental mountain range containing the Madrean sky islands, of southeastern Arizona, extreme southwestern New Mexico, and northern Sonora.

This species is a regular victim of cowbird nest parasites.

Giant cowbird

The giant cowbird (Molothrus oryzivorus) is a large passerine bird in the New World family Icteridae. It breeds from southern Mexico south to northern Argentina, and on Trinidad and Tobago. It may have relatively recently colonised the latter island.

It is associated with open woodland and cultivation with large trees, but is also the only cowbird that is found in deep forest. It is a quiet bird, particularly for an icterid, but the male has an unpleasant screeched whistle, shweeaa-tpic-tpic. The call is a sharp chek-chik. They are also very adept mimics.

Like other cowbirds, it is a brood parasite, laying its eggs in the nests of oropendolas and caciques. The eggs are of two types, either whitish and unspotted, or pale blue or green with dark spots and blotches. 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.

The male giant cowbird is 36 cm (14 in) long, weighs 180 g (6.3 oz) and is iridescent black, with a long tail, long bill, small head, and a neck ruff which is expanded in display. The female is smaller, averaging 28 cm (11 in) long and weighing 135 g (4.8 oz). She is less iridescent than the male, and the absence of the neck ruff makes her look less small-headed. Juvenile males are similar to the adult male, but browner, and with a pale, not black, bill.

This gregarious bird feeds mainly on insects, and some seeds, including rice, and forages on the ground or in trees. It rarely perches on cattle, unlike some of its relatives, but in Brazil it will ride on capybaras as it removes horse flies.

Golden-fronted greenlet

The golden-fronted greenlet (Pachysylvia aurantiifrons) is a small passerine bird in the vireo family. It breeds in Panama, Colombia, Venezuela and Trinidad.

It is a bird of forests and secondary growth which builds a deep cup nest suspended from a tree branch or vine. The typical clutch is three white eggs, which are marked with brown. This species is parasitised by the shiny cowbird.

The adult golden-fronted greenlet is 12 cm long and weighs 9.5 g. It is mainly green on the upperparts, with browner wings and tail, and a cinnamon tinge to the front and sides of the head. The underparts are yellow. The call is a chee-veee.

Golden-fronted greenlets feed on insects and spiders taken from the upper and middle levels of tree foliage. They often form small flocks.

Grayish baywing

The grayish baywing (Agelaioides badius), formerly known as the bay-winged cowbird, is a species of bird in the family Icteridae. It is currently placed in the genus Agelaioides but has traditionally been placed in the genus Molothrus. It is found in the northern half of Argentina, Bolivia, Uruguay, Paraguay and southern and central Brazil, The isolated population in north-eastern Brazil is usually now considered a separate species, the pale cowbird or pale baywing (Agelaioides fringillarius). The greyish baywing has been recorded as a vagrant in Chile.

Pale-headed brush finch

The pale-headed brush finch (Atlapetes pallidiceps) is a species of bird in the Passerellidae family. It is endemic to arid areas with low scrub at altitudes of 1,650–1,800 m (5,410–5,910 ft) in south-central Ecuador.

It is threatened by habitat loss and the nest-parasitic shiny cowbird. Most of its tiny known range, estimated at only 1 km2 by BirdLife International, is within the Yunguilla reserve, which, following the rediscovery of this species in 1998, was set up by the Jocotoco Foundation. Following intensive management, including the removal of cowbirds, the population of the pale-headed brush finch is currently increasing. Further increase, however, may be limited by a lack of suitable habitat.

Pale baywing

The pale baywing (Agelaioides fringillarius), formerly known as the pale cowbird, is a species of bird in the family Icteridae. It is currently placed in the genus Agelaioides, but has traditionally been placed in the genus Molothrus. It is found in north-eastern Brazil.

It is primarily found in the Caatinga and the northern Cerrado.


Pandanaris convexa is an extinct cowbird genus described in 1947 by Alden H. Miller.

Prairie warbler

The prairie warbler (Setophaga discolor) is a small songbird of the New World warbler family.

These birds have yellow underparts with dark streaks on the flanks, and olive upperparts with rusty streaks on the back; they have a yellow line above the eye, a dark line through it, and a yellow spot below it. These birds have black legs, long tails, two pale wing bars, and thin pointed bills. Coloring is duller in female and immatures.

Their breeding habitats are brushy areas and forest edges in eastern North America. The prairie warbler's nests are open cups, which are usually placed in a low area of a tree or shrub. Incubation period is 12 to 13 days.These birds are permanent residents in the southern parts of their range. Other birds migrate to northeastern Mexico and islands in the Caribbean.

Prairie warblers forage actively on tree branches, and sometimes fly around with the purpose of catching insects, which are the main food source of these birds.

Prairie warblers have two categories of songs, referred to as Type A and Type B. Type A songs are typically a series of ascending buzzy notes. The B songs are an ascending series of whistled notes that often contain some buzzy notes. Compared to A songs, the B songs are lower in pitch, have fewer, longer notes. The total song length is longer as well in Type B songs. The use of these two song categories is associated with certain contexts. A songs are sung throughout the day when males first arrive on their breeding grounds. Once males are paired they begin to sing B songs during the dawn chorus and then will intersperse A songs in their singing during the rest of the day. During this later period of singing A songs are typically used near females, near the nest, and in the center of their territories. In contrast B songs are used when interacting or fighting with other males and near the borders of their territories.

Part of their call note repertoire is a tsip call. During dawn, chorus B songs are interspersed with rapid loud "check" calls.

These birds wag their tails frequently.

The numbers of these birds are declining due to habitat loss; this species also suffers from nest parasitism by the brown-headed cowbird.

Screaming cowbird

The screaming cowbird (Molothrus rufoaxillaris) is an obligate brood parasite belonging to the family Icteridae and is found in South America. It is also known commonly as the short billed cowbird.

Shiny cowbird

The shiny cowbird (Molothrus bonariensis) is a passerine bird in the New World family Icteridae. It breeds in most of South America apart from the most dense jungles, mountains and deserts (although spreading into these habitats as they are modified by humans), the coldest southernmost regions (e.g. Tierra del Fuego), and on Trinidad and Tobago. It has relatively recently colonised Chile and many Caribbean islands, and has reached the United States, where it is probably breeding in southern Florida. Northern and southernmost populations are partially migratory. It is a bird associated with open woodland and cultivation. The male’s song is a purr and whistle, purr purr purrte-tseeeee. The male’s call is a sharp whistled tsee-tsee, but the female makes a harsh rattle.

Like most other cowbirds, it is an obligate brood parasite, laying its eggs in the nests of many other bird species, such as (in Brazil) the rufous-collared sparrow and the masked water tyrant. The eggs are of two types, either whitish and unspotted, or pale blue or green with dark spots and blotches. The host’s eggs are sometimes removed, and if food is short their chicks may starve, but larger host species are less affected. The incubation period of 11–12 days is shorter than that of most hosts. Extermination of the shiny cowbird within the tiny range of the pale-headed brush finch has resulted in a population increase in this critically endangered species.

The male shiny cowbird is all black with an iridescent purple-blue gloss. The smaller female is dark brown in plumage, paler on the underparts. She can be distinguished from the female brown-headed cowbird by her longer, finer bill, pale supercilium and stronger face pattern. There is an all-black plumage variation, and the northern subspecies M. b. cabanisii of Panama and northern Colombia is paler than the nominate M. b. bonariensis. Juveniles are like the female but more streaked below. There is some variation in size across the range, with the race of M. b. minimus from northern South America and the West Indies being the smallest at 31 to 40 g (1.1 to 1.4 oz) and 18 cm (7.1 in) in length and M. b. cabanisii being the largest at 55 to 65 g (1.9 to 2.3 oz) and 22 cm (8.7 in) on average.This abundant and gregarious bird feeds mainly on insects and some seeds, including rice, and forages on the ground or perches on cattle.

White-browed meadowlark

The white-browed meadowlark (Leistes superciliaris) is a passerine bird in the New World family Icteridae. It was formerly named white-browed blackbird but is not closely related to the red-winged blackbird group.The white-browed meadowlark breeds in north-eastern Brazil and in southern South America from south-western Brazil through Paraguay, Uruguay and Argentina. Southern populations are partially migratory.

Like other meadowlarks, it is a bird associated with open country, including moist grasslands, pasture and cultivation, preferably with the odd bush or fence post for males to use as a songpost. In display the male flies up to 10 m in the air, then parachutes down on folded wings whilst singing an initially buzzing song, followed by a series of notes TZZZZZZ-teee-chu-chu-chak-chak. The call is a short chuck.

The white-browed meadowlark builds a deep grass-lined open cup nest on the ground amongst tall grasses, with several nests often close together. The normal clutch is three to five reddish brown-blotched greenish eggs. This species is often parasitised by the shiny cowbird, and on one occasion 19 cowbird eggs were found with one meadowlark egg in a nest.

The white-browed meadowlark is a small icterid. The male has mainly black plumage, apart from a bright red throat, belly and wing epaulets, and a white supercilium. The female has buff edged dark brown upperpart feathers, buff underparts, and pale streaks through the crown and eye. Juveniles resemble the female, but are paler.

This species is very closely related to the red-breasted meadowlark, L. militaris, which breeds further north, and was formerly considered to be subspecies of that bird. The male white-browed is easily distinguished by his bright white supercilium, but females of the two species are almost identical. The female red-breasted meadowlark is longer billed, smaller, and shorter winged than the white-browed, with more red and less streaking on the underparts.

This gregarious bird feeds mainly on insects and some seeds, including rice, and forages on the ground like a bobolink.

The white-browed meadowlark has benefited from the more open habitat created by forest clearance and ranching, and is extending its range.


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