Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) RESIDENT: from eastern Panama south through most of South America to central Chile and central Argentina; during 1900s range expanded though Lesser and Greater Antilles, reaching Puerto Rico in 1955 and Hispaniola in 1970s (AOU 1998, Post and Wiley 1977). Established on Barbados (probably an introduction) and Grenada (AOU 1998). Has reached Cuba, Curacao, and the Bahamas (Derbot and Prins 1992, Carib. J. Sci. 28:104-105; Baltz 1995). Spreading with deforestation along rivers in Amazonia (Ridgely and Tudor 1989). Expansion in range has accompanied large-scale habitat alterations (deforestation) associated with agriculture and animal husbandry (Post and Wiley 1977, Cavalcanti and Pimentel 1988). Now established in southern Florida and occurring rarely to western Florida and southern Georgia, and casually west to central Texas and Oklahoma and north to North Carolina; accidental in Maine (AOU 1998).
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Length: 20 cm
Weight: 39 grams
Habitat and Ecology
Comments: Various habitats but prefers open areas (Cruz et al. 1989). Partly open situations with scattered trees, open woodland, cultivated lands, pastures, marshes, and around human habitation (AOU 1983).
Brood parasite and host generalist; lays eggs in nests of many other bird species. In Puerto Rico (and elsewhere), heavily parasitized species include DENDROICA PETECHIA, VIREO ALTILOQUUS, MYIARCHUS ANTILLARUM, and various icterids, including ICTERUS DOMINICENSIS and AGELAIUS XANTHOMUS (Wiley 1985, Post et al. 1993). See Cavalcanti and Pimentel (1988) for hosts in central Brazil.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
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.
In Puerto Rico, common along southwestern coast June-October; few remain in coastal zone after October (Post and Wiley 1977). In U.S., apparently permanent residents south of Tampa, Florida, but numbers increase in northern part of range, possibly as a result of incursions from the Greater Antilles (Post et al. 1993).
Implicated in decline of several island bird populations, including yellow-shouldered blackbird in Puerto Rico. Other host species that should be monitored for possible cowbird-induced decline include Puerto Rican flycatcher, black-whiskered vireo, black-cowled oriole, and troupial (Cruz et al. 1989). Brood parasitism reduces nesting success and productivity of hosts (Wiley 1985).
Roosts communally in large numbers (1000s in Puerto Rico) with AGELAIUS XANTHOMUS and QUISCALUS NIGER (Post and Wiley 1977); otherwise occurs alone or more frequently in small loose groups. Females commuted daily about 4 kilometers between feeding and breeding areas (Woodworth 1993).
Life History and Behavior
In Puerto Rico, lays eggs mainly March-July (Wiley 1988). In nests of AGELAIUS XANTHOMUS, lays 2-5 eggs per nest (Post and Wiley 1977). Incubation and rearing of young by host species; up to 3-4 cowbirds may fledge from nest of certain hosts (Wiley 1985).
Molecular Biology and Genetics
Barcode data: Molothrus bonariensis
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 bonariensis
Public Records: 10
Specimens with Barcodes: 22
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N2N,N3B : N2N: Imperiled - Nonbreeding, N3B: Vulnerable - Breeding
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Management Requirements: Easily captured in traps baited with grain; trapping of cowbirds apparently is the most effective management technique for recovery of parasitized bird populations (Wiley 1985; see also Heisterberg and Nunez-Garcia 1988).
Relevance to Humans and Ecosystems
Comments: When present in large numbers, can have important effects on corn and rice cultivation (Borja 1990).
|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (November 2010)|
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 a 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.
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