Bronze-brown Cowbird

The bronzed cowbird, Molothrus aeneus, is a small icterid bird with a distinctive appearance. The male is resplendent with green-bronze, gloss-black plumage and, during the breeding season, exhibits striking red eyes, which otherwise are brown. He measures about 20 cm in length and weighs approximately 68 g. The female, slightly smaller at 18.5 cm and 56 g, is less conspicuous with her dull black feathers and a brown underbelly, complemented by brown eyes. Juveniles resemble the female but can be identified by grey feather fringes.

Identification Tips

To identify the bronzed cowbird, look for the male's glossy green-bronze plumage and red eyes during the breeding season. Outside of this period, their eyes are brown. Females and young birds are duller with brown underbellies and eyes, with juveniles sporting grey feather edges.

Habitat

Bronzed cowbirds are typically found in farmland, brush, and feedlots. They adapt to very open habitats outside the breeding season and roost in dense woodlands.

Distribution

These birds breed across a range that includes the U.S. states of California, Arizona, New Mexico, Texas, and Louisiana, extending south through Central America to Panama. The subspecies M. a. loyei inhabits the southwestern United States and northwestern Mexico, M. a. assimilis is found in southwestern Mexico, and the nominate subspecies, M. a. aeneus, resides in South Texas and from eastern Mexico to central Panama.

Behaviour

Bronzed cowbirds are obligate brood parasites, laying their eggs in the nests of other bird species, such as Prevost's ground-sparrows and white-naped brush finches. The cowbird chicks are then raised by the host parents, often at the expense of the host's own offspring. These birds forage in open areas, frequently near cattle, and leave the nest rapidly after hatching, within 10 to 12 days.

Diet and Feeding

The diet of the bronzed cowbird primarily consists of seeds and insects. During the breeding season, they also consume snails as a source of calcium.

Conservation status

The bronzed cowbird is currently listed as Least Concern by the IUCN, indicating that it is not at immediate risk of population decline or habitat loss.

Similar Species

The bronze-brown cowbird, found on the Caribbean coast of Colombia, was once considered an isolated population of the bronzed cowbird but is now recognized as a separate species.