Cowbirds are a group of birds belonging to the genus Molothrus in the icterid family. They are best known for their brood parasitism, where females lay eggs in the nests of other bird species, leaving the host parents to raise the cowbird chick. The most widespread and best-known cowbird species is the brown-headed cowbird, Molothrus ater, which is found throughout North America. However, there are several other cowbird species found in the Americas that parasitize other birds’ nests. In this article, we will discuss some of the other cowbird species that resemble and act like the brown-headed cowbird.
Shiny Cowbird
The shiny cowbird, Molothrus bonariensis, is probably the cowbird species that most closely resembles the brown-headed cowbird in appearance and behavior. Like the brown-headed, the shiny cowbird is sexually dimorphic, meaning males and females look different. Shiny cowbird males are all black with a purple-blue gloss on their feathers. Females are dull gray-brown, similar in coloration to female brown-headed cowbirds.
Shiny cowbirds have a widespread distribution from Mexico through Central America into most of South America. They occupy open and semi-open habitats and are sometimes found in urban areas. Like brown-headed cowbirds, they parasitize a wide variety of hosts, including warblers, vireos, sparrows, wrens, thrushes, and blackbirds. Their egg coloration and pattern allows their eggs to mimic those of some of their common hosts.
Comparison to Brown-headed Cowbird
In body size, shape, and bill shape, shiny cowbirds closely match brown-headed cowbirds. Their eggs also look similar – white with brown speckling. Shiny cowbird behavior mirrors brown-headeds as well, including parasitism of over 220 host species, loud vocalizations, and flocking habits. The main differences are the male’s glossy plumage and a larger range confined to Central and South America.
Giant Cowbird
The giant cowbird, Molothrus oryzivorus, lives up to its name and is substantially larger than other cowbirds at 20-24 cm (8-9.5 inches) long. It is found from Mexico south to northern Argentina and central Brazil. As its name suggests, giant cowbirds parasitize larger host species than other cowbirds. Common hosts include oropendolas, caciques, grackles, and blackbirds. They are sometimes called “screaming cowbirds” due to their exceptionally loud songs.
Comparison to Brown-headed Cowbird
While giant cowbirds are much larger than brown-headed cowbirds, they have a similar stocky body profile and short, conical bill. Their plumage is also somewhat similar, with black bodies and light brown heads. However, the giant cowbird’s head and neck are darker gray-brown compared to the lighter brown on brown-headed cowbirds. Females of the two species look more alike than males, both being rather plain light brown and gray. Giant cowbirds have very different vocalizations and parasitize much larger host species than brown-headeds.
Bronzed Cowbird
The bronzed cowbird, Molothrus aeneus, is a stocky black cowbird with body plumage that has a bronzy gloss in good lighting. It is found from southern Texas through Mexico and Central America into northwestern Colombia and northwestern Venezuela. Bronzed cowbirds often associate with brown-headed cowbirds where their ranges overlap in the United States.
Comparison to Brown-headed Cowbird
In body profile, shape, and size, bronzed cowbirds closely match brown-headed cowbirds. However, unlike brown-headeds, bronzed cowbird males are mostly black with a purplish-bronze gloss on the body, while females are plain gray-brown. Their songs are a series of short, nasal notes and differ from the more varied vocalizations of brown-headed cowbirds. Bronzed cowbirds parasitize a wide variety of small passerines, especially warblers and vireos. In areas where they co-occur with brown-headed cowbirds, they tend to choose smaller host species.
Screaming Cowbird
The screaming cowbird, Molothrus rufoaxillaris, of South America gets its name from its loud, piercing vocalizations. Males are mostly glossy black with a gray head and thick bill. Females are plain gray with a paler throat. Screaming cowbirds range from southeastern Brazil to Argentina, Paraguay, Uruguay and southern Bolivia.
Comparison to Brown-headed Cowbird
While the male screaming cowbird’s plumage is similar to the brown-headed, its grey head, thicker bill, and different vocalizations sets it apart. Female screaming cowbirds could potentially be confused with female brown-headeds due to similar plain, gray-brown plumage. However, screaming cowbird females have a pale throat patch that brown-headeds lack. Screaming cowbirds exclusively parasitize large icterid hosts, especially chopi blackbirds, while brown-headed cowbirds have a much more diverse range of hosts.
Andean Cowbird
The Andean cowbird, Molothrus armenti, is found in the Andes Mountains from western Venezuela to Bolivia. The male is mostly black with a brick red hood over its head, neck and chest. The female is gray-brown on the head, neck, back and chest with heavy dark streaking on the underparts.
Comparison to Brown-headed Cowbird
While the male Andean cowbird’s black and red color pattern differs markedly from the brown-headed cowbird, females could potentially cause confusion due to similar gray-brown overall plumage. However, the streaked underparts helps distinguish Andean females, as brown-headed cowbirds have an unmarked, plain belly and breast. Andean cowbirds are also somewhat larger than brown-headeds on average. They parasitize various icterids and emberizids in their mountainous habitat, while brown-headed cowbirds use more diverse hosts in a wider range of habitats.
Bay-winged Cowbird
The bay-winged cowbird, Molothrus badius, lives up to its name with striking rufous-colored wings in the male. Found from Panama to northern Argentina and southern Brazil, it is the smallest cowbird species. It often associates with shiny cowbirds where their ranges overlap. Female bay-winged cowbirds are plain gray-brown.
Comparison to Brown-headed Cowbird
The male bay-winged cowbird’s bay-colored wings make it distinctive compared to the all-black adult male brown-headed cowbird. Females look fairly similar, both being plain gray-brown. However, the bay-winged cowbird is smaller and has a less stocky build overall. Bay-winged cowbirds parasitize various small hosts, especially warblers, tanagers and tyrant flycatchers, while brown-headed cowbirds use a wider range of hosts. Their vocalizations also differ significantly.
Red-eyed Cowbird
The red-eyed cowbird, Molothrus aeneus, is appropriately named for its bright red eyes. The male is mostly black with a brown head, while the female is gray with a dull orange throat and breast. It is endemic to the Caribbean islands of Puerto Rico and Hispaniola. Red-eyed cowbirds parasitize a wide variety of hosts, including tanagers, warblers, thrushes and saltators.
Comparison to Brown-headed Cowbird
Aside from the diagnostic red eyes, the male red-eyed cowbird differs from the brown-headed in its brown head coloration. Females could potentially cause some confusion with brown-headeds due to similar overall gray plumage. However, the reddish throat and breast of the red-eyed separate it from the plain brown-headed female. Red-eyed cowbirds are also smaller on average and have different vocalizations. They have a much smaller, island-restricted range compared to the widespread brown-headed cowbird.
Comparison Table of Cowbird Species
| Species | Range | Size | Male Plumage | Female Plumage | Common Hosts |
|---|---|---|---|---|---|
| Brown-headed Cowbird | North America | 16-19 cm | Black with brown head | Plain gray-brown | Wide variety of small passerines |
| Shiny Cowbird | Mexico to South America | 16-19 cm | Black with bluish gloss | Plain gray-brown | Warblers, vireos, sparrows, blackbirds |
| Giant Cowbird | Mexico to South America | 20-24 cm | Black with dark gray-brown head | Plain gray-brown | Oropendolas, caciques, grackles, blackbirds |
| Bronzed Cowbird | Southwest US to South America | 16-19 cm | Black with bronze gloss | Plain gray-brown | Warblers, vireos |
| Screaming Cowbird | South America | 19-22 cm | Black with gray head | Plain gray with pale throat | Large icterids like chopi blackbird |
| Andean Cowbird | Venezuela to Bolivia | 20-25 cm | Black with red hood | Gray-brown with streaked underparts | Various icterids and emberizids |
| Bay-winged Cowbird | Panama to South America | 14-16 cm | Black with rufous wings | Plain gray-brown | Warblers, tanagers, tyrant flycatchers |
| Red-eyed Cowbird | Caribbean islands | 16-18 cm | Black with brown head | Gray with orange throat/breast | Tanagers, warblers, thrushes, saltators |
Identification Tips
Here are some key identification tips for distinguishing lookalike cowbird species:
Males
- Look at the coloration on the body and head – is it completely black, or does it have a hood/cap of a different color?
- Note any glossy or metallic sheen to the black feathers.
- Pay attention to eye color – most are dark-eyed, but the red-eyed cowbird is distinctive.
- Note any non-black colors on the wings, chest, or other plumage.
Females
- Look for differences in breast/throat color – some have pale throats while brown-headeds are plain.
- Note if there is streaking or spotting on the underparts.
- Assess overall size and proportions – some species are noticeably larger or smaller than brown-headeds.
- Listen for vocalizations – the screaming and giant cowbirds have very distinctive songs.
Range
- Consider the geographic range – species like the red-eyed and Andean cowbird have much more localized ranges than widespread brown-headeds.
- Study range maps to determine if a confusing species occurs in your area.
Conclusion
While several other cowbird species share physical and behavioral similarities with the ubiquitous brown-headed cowbird, careful attention to details like size, plumage colors, vocalizations, range, and host preferences allows identification of lookalike species. Features like red eyes, distinct caps or hoods, pale throats, streaked underparts, and unusual dimensions compared to brown-headeds serve to distinguish most other cowbirds. Familiarity with which species occur in your region goes a long way toward confident identification. With practice and attention to diagnostic characteristics, birders can adeptly recognize many cowbird doppelgangers that resemble brown-headeds at first glance.
