occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: RESIDENT: from extreme southeastern California, western and central Arizona, southwestern New Mexico, western Chihuahua, and western and southern Texas south to Panama; locally uncommon to fairly common in coastal Caribbean Colombia in northern Magdalena (Ridgely and Tudor 1989). Northern populations partially migratory.
Length: 22 cm
Weight: 67 grams
Comments: Open country, ranches, roadside thickets, open woods, parks, orchards, pastures, around human habitation, open areas and fields with scattered bushes and low trees. BREEDING: Lays eggs in nests of other species; see Carter (1986) and Clotfelter and Brush (1995, Condor 97:814-815) for hosts in southern Texas, Stiles and Skutch (1989) for hosts in Costa Rica.
Habitat and Ecology
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Partially migratory in part of northernmost breeding range.
Comments: Eats insects, grain, seeds; forages in open fields and pastures, often associated with cattle, from the skin of which insects and parasites may be obtained (Terres 1980).
Females pierce eggs of host and previously laid cowbird eggs (Carter 1986).
Life History and Behavior
Lifespan, longevity, and ageing
Lays eggs (usually 1 per nest) in nests of various bird species (Carter 1986, Stiles and Skutch 1989). Incubation 12-13 days, by host. Young leaves nest at about 11 days, fed by host for additional 2 weeks.
Molecular Biology and Genetics
Barcode data: Molothrus aeneus
There are 7 barcode sequences available from BOLD and GenBank. Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species. See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Molothrus aeneus
Public Records: 8
Specimens with Barcodes: 9
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: N4N,N5B : N4N: Apparently Secure - Nonbreeding, N5B: Secure - Breeding
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Widespread and common in agricultural areas.
IUCN Red List Assessment
Red List Category
Red List Criteria
It breeds from the southern U.S. states of California, Arizona, New Mexico, Texas, and Louisiana south through Central America to Panama. An isolated population on the Caribbean coast of Colombia is sometimes treated as a separate species, the bronze-brown cowbird (M. armenti).
The male bronzed cowbird is 20 cm long and weighs 68 g, with green-bronze glossed black plumage and red eyes. The female is 18.5 cm long and weighs 56 g. She is duller black above and browner below. Young birds are like the female but have grey feather fringes.
Like all cowbirds, this bird is a 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 yellow-throated brush finch.
- Stiles and Skutch, A guide to the birds of Costa Rica ISBN 0-8014-9600-4
- Lowther, P. E. 1995. Bronzed Cowbird (Molothrus aeneus). In The Birds of North America, No. 144 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, and The American Ornithologists’ Union, Washington, D.C.
Names and Taxonomy
Comments: Composed of two groups formerly considered separate species: aeneus (Bronzed Cowbird) and armenti (Bronze-brown Cowbird, of South America) (AOU 1983, 1998). Often placed in genus Tangavius (AOU 1998).