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Shiny Cowbird | Molothrus bonariensis
Glanskoevogel | Tordo renegrido
The Shiny Cowbird is a brood parasite from South America that lays its eggs in other birds' nests. In recent decades it has spread via Colombia into Panama and Costa Rica, and via the Caribbean to the Yucatán Peninsula.
Voice
The song is a rapid series of bubbling, liquid whistles, often starting with a few low, guttural notes. The call is a short chuk; in flight also a high whistle.
Recording: Cristian Pinto Fernandez — CC BY-NC-SA 4.0 · shortened to the first 60 s, mono · xeno-canto
Identification
18–21 cm. Male entirely black with a strong purple-blue gloss, especially on head and back; eye dark. Bill short, pointed and conical, slightly slimmer than in the other cowbirds. Female plain grey-brown, with a faint pale supercilium and a slightly paler throat; underparts sometimes faintly streaked. Juveniles resemble the female but are more clearly streaked below.
Confusion species
Bronzed Cowbird Molothrus aeneus is bulkier, with a thicker neck, a red eye and a bronze-green rather than purple-blue gloss; the female is blackish-brown or, in western Mexico, grey-brown with a red eye. The male Brown-headed Cowbird Molothrus ater has a brown head. Males can also be mistaken for Melodious Blackbird Dives dives, which is larger, with a longer tail and a longer bill.
Habitat
Open and semi-open country: cattle pastures, fields, gardens, parks and villages, marsh edges and savannas. It avoids closed forest. It forages on the ground, often in groups and with cattle, and eats seeds and insects. It lays its eggs in the nests of more than two hundred other species, mainly small songbirds.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
Widespread in South America, and since the twentieth century has spread through the Caribbean islands to Florida. In the guide area common in Panama and over most of Costa Rica; scarcer but spreading in Nicaragua. In Mexico established in the north-east of the Yucatán Peninsula, especially Quintana Roo; very rare in Belize.
- Resident
- dark = core range, pale = thinly spread
How and when to look
Best seen in cattle pastures or on village lawns, where small groups of males forage on the ground; in mixed flocks watch for the difference in gloss and eye colour from Bronzed Cowbird.
Conservation status
Not threatened (LC). Common and still spreading. Because it parasitises the nests of other birds, it can be a threat to rare species with small ranges.
Scientific name
Molothrus bonariensis | (Gmelin, 1789)
Gmelin described the species in 1789 as Tanagra bonariensis; because it was later moved to another genus, the author and year stand in brackets. The genus Molothrus was introduced in 1832 by Swainson. Molothrus is Greek, from mōlos 'struggle' and thrōskō 'to impregnate', perhaps after the brood parasitism or the males' courtship contests. bonariensis means 'of Buenos Aires', where the species was described from. The specimen the first description was based on came from Buenos Aires, Argentina.