|Species: Brown Headed Cowbird
Cowbirds are easily recognized as members of the blackbird family
(Icterids). They are identified by a dark brown head on a black body
that has a green iridescent sheen. The bill is straight, pointed and
looks relatively short and thick.
Gregarious birds, they are often found in mixed flocks with other
blackbirds and starlings. These flocks can number in the hundreds of
thousands in the fall and winter after the breeding season.
During breeding season their range is widespread across North
America, spending winters in the Southeastern US and Mexico. They
have a somewhat dubious claim to fame as the most well-known North
American practitioners of brood parasitism, where the young are
foisted off into another species’ nest to be hatched and raised.
Adults are about 19 cm long, and weigh about 44 grams, with short
tails and pointed wings. Straight, stout bill, some say it is almost
Black body with a glossy green sheen, brown head.
Gray-brown overall, with a paler head and underparts. The breast has
fine, faint streaks and the female has a dark eye.
Gray-brown, back feathers with a pale fringe giving the back a scaly
appearance. Underparts paler, with distinct fine streaks on the
Bronzed Cowbirds are shorter-tailed and stockier with a thick ruff
of feathers around the neck; Shiny Cowbirds have slenderer bills and
are a uniform glossy black. (Both are rare in the Pacific
Northwest.) Brewer’s Blackbirds can be distinguished by a glossy
blue-black head and a yellow eye.
Roost colonially, tend to congregate in large mixed flocks in open
fields. They eat grain and insects, foraging on the ground. Flight
is direct with constant wingbeats.
Tend to congregate in open field, often near livestock, but will
hang around forest edges during breeding season to utilize host
nests. Habitat can vary with time of day, with breeding behavior
taking place in the morning (near woodland nests) and foraging in
open fields happening later in the day.
Unable to build
their own nests, Brown-headed Cowbirds rely on other birds to hatch
and rear their young by laying eggs in other species’ nests. When
placing her egg in a host nest, a female cowbird will often peck or
dislodge a host egg. A female can lay as many as 40 eggs in a
season. While the young cowbirds may not oust host eggs and young
from the nest per se, cowbird eggs do hatch sooner, grow faster and
put a lot of pressure on the host young and parent by competing for
food. If the host species is larger them the cowbirds, the host
species is usually able to bear the burden, but in smaller species
the young are usually out-competed and starve. For this reason
cowbirds are considered to be a contributing factor to the decline
of some songbird species. They lay their eggs in the nests of over
220 species, with the most common being the Yellow Warbler, Song and
Chipping sparrows, Red-eyed Vireo, Eastern and Spotted towhees, and
associated with American Bison, the Brown-headed Cowbird’s range has
increased with the clearing of fields and the introduction of
livestock. It is a species of lowest concern, having thrived with
human influence beginning in the 1800s as forests were cleared and
the spread of agricultural lands increased its feeding habitat.
The Sibley Guide to Bird Life and Bird Behavior– David Sibley
The Sibley Guide to Birds – David Sibley
The Birder’s Handbook – Paul Erlich
All About Birds, Cornell Lab of Ornithology:
As a brood parasite, Brown-headed Cowbird capture rate
(2010-2012; standardized as birds captured per 100 net
hours) peaks in mid-summer during the breeding season.
Cowbirds are short distance migrants, moving south for the
winter as seen by our zero capture rate between September -