Though an attractive and remarkably adaptable bird, the brown-headed cowbird is often reviled for its habit of laying eggs in the nests of other species, threatening the nest success of smaller passerines. Birders who learn more about this blackbird can also learn about its admirable qualities, as well as how to help protect their other nesting songbirds.
Common Name:
Brown-Headed Cowbird, Common Cowbird, Cowbird
Scientific Name:
Molothrus ater
Scientific Family:
Appearance:
- Bill: Short, conical, pointed, dark
- Size: 7.5 inches long with 13-inch wingspan, stocky body shape
- Colors: Black, brown, gray-brown, iridescent
- Markings: Dimorphic species. Males have a prominent chocolate brown hood that may show darker near the base of the bill. The rest of the male's plumage is solid black overall but may show a faint iridescent green sheen in bright light. Females are grayish-brown overall, with minor streaking on the back and underparts that can vary in intensity. A faint malar stripe can be seen on the throat. For both genders the eyes, legs and feet are dark. Juveniles resemble female birds but are lighter and paler overall and may have a stronger streaked or scaled appearance. When juvenile males are molting into adult plumage, they have patchwork brown and black plumage.
Foods:
Insects, seeds, grain, spiders, fruit (See: Omnivorous)
Habitat and Migration:
Brown-headed cowbirds are adaptable and prefer a variety of open habitats, including open woodlands, forest edges, grasslands, orchards, agricultural areas, pastures and suburbs. They are frequently found in areas near livestock. They can be found year-round in the eastern and central United States from New Hampshire to Iowa, Oklahoma, Texas, southern New Mexico and Arizona and along the Pacific coast, as well as into central Mexico. In summer, the breeding range extends further north to include all of the western United States and southern Canada, though they avoid heavily forested regions. In winter, these neotropical migrants can be found throughout Mexico, and very rare vagrant sightings are reported in Europe.
Vocalizations:
These birds have a liquid warbling song comprised of high, piercing notes, especially at the end of the song. Females have a harsh, rough chatter call, and other calls include clicks and long, drawn out whistles.
Behavior:
These are gregarious birds that gather in tremendous flocks in the fall and winter, often mixed with other species such as red-winged blackbirds and European starlings, and these foraging and roosting flocks may number millions of birds. During the breeding season they are more often solitary or found in pairs or small groups. While foraging, they walk along the ground and often hold their tails cocked up, or may pause and look upward at times.
Reproduction:
Brown-headed cowbirds are polygamous, promiscuous birds that do not build nests or tend their own young. Instead, they are brood parasites – the female bird will lay a single oval, light blue egg with brown flecks in another species' nest and leave it for the host birds to incubate and raise the hatchling. One female may lay 10-36 eggs in other nests, and more than 220 different species of birds have been documented as brown-headed cowbird hosts. The most common host birds include yellow warblers, song sparrows, red-eyed vireos, eastern towhees and spotted towhees.
The incubation period for a brown-headed cowbird egg is 10-14 days, which is often shorter than the incubation period for the host birds. This ensures the cowbird egg hatches first and can usurp the majority of the foster parents' care and attention, often to the detriment of the nest's own hatchlings. The hatchlings will then leave the nest in 10-12 days. During the period where the hatchlings require care, they may smother the host birds' own hatchlings or inadvertently push them from the nest.
Attracting Brown-Headed Cowbirds:
Many backyard birders prefer to avoid attracting brown-headed cowbirds in order to protect their nesting backyard species, but these birds will visit feeders offering mixed birdseed or sunflower seeds. They also often feed in areas of short grass, particularly if there is nearby grain or seeds scattered on the ground. Avoiding ground feeders and using feeders designed for smaller birds will help deter brown-headed cowbirds.
Conservation:
These are one of the most common songbirds in North America, with a total population estimated between 20 and 40 million birds. Because of their nest parasitism, they are not favored birds, and in areas where they threaten the nesting habits of endangered species, brown-headed cowbirds are often trapped and removed. Birders should be aware, however, that brown-headed cowbirds are still a protected species under the Migratory Bird Act and disturbing their eggs or harming the birds is not permitted without proper legal approval.
Similar Birds:
- Bronzed Cowbird (Molothrus aeneus)
- Shiny Cowbird (Molothrus bonariensis)
- Brewer's Blackbird (Euphagus cyanocephalus)
- Common Grackle (Quiscalus quiscula)
- Rusty Blackbird (Euphagus carolinus)
- Red-Winged Blackbird (Agelaius phoeniceus)
Photo – Brown-Headed Cowbird – Male © Dan Pancamo
Photo – Brown-Headed Cowbird – Female © Dan Pancamo
