Brown-headed Cowbird

Molothrus ater

The Brown-headed Cowbird is the only brood parasite common across North America. A female cowbird makes no nest of her own, but instead lays her eggs in the nests of other bird species, who then raise the young cowbirds.

Cool Facts

Photo taken from:
The Sibley Field Guide to Birds of Western North America by David Allen Sibley
  • The Brown-headed Cowbird is the only brood parasite common across North America. A female cowbird makes no nest of her own, but instead lays her eggs in the nests of other bird species, who then raise the young cowbirds.
  • The Brown-headed Cowbird lays eggs in the nests of many different species of birds. Recent genetic analyses have shown that some female cowbirds will use a number of different hosts, but most females specialize on one particular host species.
  • Social relationships are difficult to figure out in birds that do not build nests, but male and female Brown-headed Cowbirds are not monogamous. Genetic analyses show that males and females have several different mates within a single season.

Description

  • Size: 17-22 cm (7-9 in)
  • Wingspan: 28-36 cm (11-14 in)
  • Weight: 38-50 g (1.34-1.77 ounces)
  • Medium-sized songbird.
  • Medium-long tail.
  • Bill stout and pointed.
  • Male shiny black with brown head and neck.
  • Female dull gray-brown.
  • Eyes black.
  • Wings rather long and pointed.
  • Legs black.
Sex Differences
Male shiny black with brown head and neck, female plain gray-brown.
Male
Body, wings, and tail shiny black. Head, nape, and chest dull dark brown. Bill black. Legs black.
Female
Entirely grayish brown. Chest with dull streaks. Throat whitish. Suggestion of faint pale eyestripe. Bill gray.
Immature
Juvenile similar to female, but more distinctly streaked below. Males molting in fall may be patched black and brown.
Range Map
 
Taxonomic Hierarchy

Spotted_Sandpiper_AllAm

© 2003 Cornell Lab of Ornithology
Kingdom: Animalia
Phylum: Chordata
     Subphylum: Vertebrata
Class: Aves
Order: Passeriformes
Family: Icteridae
Genus: Molothrus
Species: Molothrus ater
     Subspecies:
  • Molothrus ater artemisiae
  • Molothrus ater ater
  • Molothrus ater obscurus
Sound
Song a pair of low "glug, glug" notes followed by slurred whistles ending on a very high pitch. Calls include a chatter and a whistled "fee-bee."

Identification and Information
See Anatomy of a Bird
Body
  • Length Range: 18-21 cm (7-8.25 in)
  • Weight: 48 g (1.7 oz)
  • Size: 2. Small (5 - 9 in)
  • Color Primary: Black, Sheen or Iridescence
  • Underparts: Black with faint green sheen.
  • Upperparts: Black with faint green sheen.
  • Back Pattern: Solid
  • Belly Pattern: Solid
  • Breast Pattern: Solid
 
Head
  • Bill Shape: Cone
  • Eye Color: Brown.
  • Head Pattern: Plain
  • Crown Color: Glossy brown
  • Forehead Color: Glossy brown
  • Nape Color: Glossy brown
  • Throat Color: Glossy brown
  • Cere color: No Data
Flight
  • Flight Pattern: Swooping direct flight with rapid wing beats.
  • Wingspan Range: 30-35 cm (11.75-13.75 in)
  • Wing Shape: Pointed-Wings
  • Tail Shape: Fan-shaped Tail
  • Tail Pattern: Solid
  • Upper Tail: Black with faint green sheen.
  • Under Tail: Black
  • Leg Color: Black
Breeding
  • Breeding Location: Forest edge, Grassland with scattered trees
  • Breeding Type: Promiscuous
  • Breeding Population: Fairly common to common
  • Egg Color: Light blue with brown flecks
  • Number of Eggs: 1
  • Incubation Days: 10 - 13
  • Egg Incubator: Both sexes
  • Nest Material: Uses nests of other species.
  • Migration: Northern birds migrate
  • Condition at Hatching: Helpless with some whitish down.

Other Names

Similar Species

  • Vacher à tête brune (French)
  • Tordo negro (Spanish)
  • Bronzed Cowbird is larger, has longer bill, larger head, shorter tail, and red eyes. Male lacks brown hood.
  • Shiny Cowbird male is entirely glossy black, but female is extremely similar to female Brown-headed Cowbird, except bill is slightly longer.
  • Brewer's Blackbird female darker brown, has dark around the eyes, and has a thinner, more pointed bill.
  • Female and juvenile Brown-headed Cowbird resemble sparrows, but are larger, completely dull gray-brown, and have unstreaked backs.

Conservation Status

Originally a bison-following bird of the Great Plains, the Brown-headed Cowbird spread eastward in the 1800s as forests were cleared. It is a common bird across most of North America, but numbers are declining in most areas. Its habit of nest parasitism can cause the decline of species with small populations, such as Kirtland's Warbler and Black-capped Vireo. You can help scientists learn more about this species by participating in the Celebrate Urban Birds! project.

Habitat

Sources used to Construct this Page:

Breeds in areas with grassland and low or scattered trees, such as woodland edges, brushy thickets, fields, prairies, pastures, orchards, and residential areas.
  • Lowther, P. E. 1993. Brown-headed Cowbird (Molothrus ater). In The Birds of North America, No. 47 (A. Poole, and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C. 
  • Woolfenden, B. E., Gibbs, H. L., and Sealy, S. G. 2002. High opportunity for sexual selection in both sexes of an obligate brood parasitic bird, the brown headed cowbird (Molothrus ater). Behavioral Ecology and Sociobiology 52: 417 425.
  • Woolfenden, B. E., Gibbs, H. L, Sealy, S. G, and McMaster, D. G. 2003. Host use and fecundity of individual female brown-headed cowbirds. Animal Behaviour 66: 95-106.
Food
Seeds and arthropods.
Behavior
Forages on ground, often in association with cows or horses. Outside of breeding season, forages in large flocks with other blackbirds.

Adult Male

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Adult Female

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Additional Photos & Video

 

All photos © 2008 Rick Swartzentrover - Free for non-profit use.

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