Shiny Cowbird Life History

Habitat

Shiny Cowbirds frequent open and semiopen habitats including mangrove forests, scrubby fields, savanna, wooded streams, urban and suburban parks, orchards, gardens, farm areas with scattered trees, and feedlots. It is one of a handful of species that benefit from deforestation in its range. In the southern part of its South American range, the Shiny Cowbird is a migrant, spending only the summer (December–February) in some areas. In the Greater Antilles, too, Shiny Cowbirds make seasonal movements between mountains and coastal lowlands, probably responding to rainfall and corresponding increases in insect populations, and the nesting activities of their host species. Back to top

Food

Shiny Cowbirds feed on invertebrates, seeds, and grains. They forage mostly on the ground, walking briskly, looking for food, which they eat with a quick gleaning or pecking motion of the bill. They also pull insects from plants while on the ground or in trees or bushes. Like many other tropical blackbird species, Shiny Cowbirds often perch in treetops to hunt insects among flowers or leaf clusters. They are surprisingly acrobatic for a cowbird, recalling an oriole when they hang upside down or creep vertically along a branch to take food. They also flock or feed with other species of blackbirds throughout their large range, sometimes eating grain in agricultural fields, around livestock, at feeding troughs and feedlots, or at bird feeding stations. They follow plows to grab earthworms and unearthed insects. Arthropod prey includes spiders, noctuid moth larvae and other caterpillars, grasshoppers, snout beetles, ground beetles, scarab beetles, click beetles, rhinoceros beetles, flies, and leafhoppers. They eat seeds of grasses, mustards, chickweed, shepherd’s purse, and other flowering plants as well as cultivated plants such as rice, millet, sorghum, and amaranth. Compared to the Brown-headed Cowbird, which has a thicker bill, the Shiny is more arboreal in its feeding habits, and its diet includes less plant matter. Back to top

Nesting

Nest Placement

As brood parasites, Shiny Cowbirds build no nest but rather lay eggs in nests of other birds.

Nest Description

No nest.

Nesting Facts

Behavior

Shiny Cowbirds are gregarious as they forage, rest, and roost in flocks of a few to over 100 birds. In the U.S., most groups are small (5 birds or so), and males usually outnumber females. As brood parasites, they lay their eggs in other species’ nests and never build their own or raise their own young. Pairs may be monogamous for several weeks, but both sexes will mate with multiple individuals during the breeding season, which is timed to coincide with the breeding of host species.

At the onset of the breeding cycle, male Shiny Cowbirds perform courtship displays from prominent areas on the ground and in flight, often singing a squeaky song similar to the Brown-headed Cowbird. Males display by raising nape feathers (ruff), partly lifting and vibrating wings, dropping the tail, and shaking their body while giving a low, gurgling call, and may chase females during displays. In courting parties, males display aggressively toward other males, and may also point the bill skyward, point and open the bill at a rival, wipe the bill on the ground or on a perch, and bow. Unheeded warning displays often result in physical clashes. Other than these aggressive behaviors, Shiny Cowbirds are not territorial and have no fixed breeding territories. During nesting season, females perch quietly and watch for nesting activity in other species, then stealthily lay an egg in another bird’s nest when unattended, often pecking and destroying the eggs of the host at the same time. Males also watch for other species building nests and sometimes destroy eggs. Shiny Cowbirds often parasitize the nests of cavity-nesting species, unlike the Brown-headed Cowbird. For most of the year, Shiny Cowbirds forage and roost in flocks, often mixed with other blackbirds, sometimes scuffling where food is highly concentrated, as at a feeding station or feeding trough.

Conservation

Shiny Cowbirds are abundant in South America and the Caribbean and are slowly expanding their range in the U.S.. Partners in Flight rates the species a 7 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Both deforestation and suburbanization may increase habitat for Shiny Cowbirds. They thrive in agricultural areas with planted grains and livestock, gathering at feedlots to eat spilled feed. Shiny Cowbirds are brood parasites and could reduce populations of species of conservation concern in the mainland United States as they expand their range—as has happened in Puerto Rico with the Yellow-shouldered Blackbird and Puerto Rican Vireo.

Credits

Lowther, Peter E. and William Post. (1999). Shiny Cowbird (Molothrus bonariensis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Partners in Flight (2019). Avian Conservation Assessment Database, version 2019.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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