The Brown-headed Cowbird (Molothrus ater) is a small songbird species found throughout much of North America. As a brood parasite, the female cowbird lays her eggs in the nests of other bird species, leaving the host parents to raise the cowbird chick. This sneaky reproductive strategy has made the Brown-headed Cowbird a species of conservation concern. Being able to properly identify and report observations of Brown-headed Cowbirds is an important way birders can help scientists track populations. But with the females’ rather nondescript plumage, it can be tricky for novice birders to confidently differentiate these birds from other similar species. This guide will walk through the key identification features to look for, as well as behaviors that set this species apart.
Range and Habitat
As a first step in potentially spotting a Brown-headed Cowbird, it is helpful to be familiar with their range and preferred habitats. Brown-headed Cowbirds are found year-round across most of the lower 48 United States. Their breeding range extends north into southern Canada and south to Central America. These birds prefer open country near trees, including farms, forest edges, parks, and backyards. They often forage in short grass, plowed fields, cattle pastures, and under feeders. During migration and winter they may form large mixed flocks with other blackbird species.
Size and Shape
Brown-headed Cowbirds are considered a medium-sized blackbird, measuring 6.3–7.9 inches in length with a wingspan around 12.2–13.4 inches. They have a short finch-like conical bill and a long tail that appears rounded or squared off when perched. Their body shape is plump and round compared to other birds. When standing, the body is held in a horizontal posture. Overall, the shapes and proportions give Brown-headed Cowbirds a chunky, bull-headed profile.
Plumage
The plumage patterns of male and female Brown-headed Cowbirds can be distinctive:
Males:
– Head, neck, and breast are a warm chocolate brown color. This gives rise to their common name.
– The rest of the body feathers are glossy black with metallic green and purple iridescence most visible in bright light.
– Eyes are pale yellow.
– Legs and feet are black.
Females:
– Streaked gray-brown overall with a pale throat.
– The crown and nape feathers are darker brown.
– The breast and sides are heavily streaked.
– The eyes are dark brown.
– Legs and feet are grayish-brown.
The female’s drab camouflaging plumage allows her to sneak into the nests of other songbirds undetected. Juveniles resemble adult females but are darker overall.
Behaviors
Paying attention to behavior is key for identifying Brown-headed Cowbirds:
– They are extremely social, gathering in large flocks of 20 to 200 or more birds. Even during breeding season they do not pair off, the males simply following the females and trying to mate with them.
– They walk on the ground while foraging in fields, taking seeds and insects with strong bites of their thick bill.
– The flight style is bouncy with hurried flaps. They do not ride air currents and soar like hawks.
– Listen for short metallic “chink” and gurgling “glug-glug” vocalizations. The male’s song is a bubbly phrase of repeated notes.
– Watch for the sneaky female slipping into host nests to lay her eggs when the owners are away. She may remove an existing egg to make room for her own.
Common Lookalikes
The Brown-headed Cowbird’s plumage can cause it to be confused with certain other birds, especially the females and juveniles. Compare with these common lookalikes:
Red-winged Blackbird: Males are solid black with bright red and yellow shoulder patches. Females are brown-streaked but have a pale median crown stripe. Both have pointed conical bills.
Common Grackle: Larger with longer legs and tail; long pointed bill. Iridescent males have bronzy bodies while females are brown with pale spotting.
European Starling: Similar chunky shape but with short tail and triangular yellow bill; winter birds and juveniles heavily spotted.
Rusty Blackbird: Smaller with thinner bill. Breeding males are black with rust-colored highlights; females are dark gray with pale eye stripe.
Identifying Brown-headed Cowbird Eggs
Since the Brown-headed Cowbird lays its eggs parasitically in other species’ nests, another identification challenge is recognizing their eggs among the host’s own eggs. Here are tips for cowbird egg identification:
Egg Size
Cowbird eggs are about 0.8 inches long. This is smaller than many host species’ eggs, including cardinals, robins, and thrashers. But it may match the size of eggs from smaller hosts like warblers and vireos.
Egg Shape
The cowbird egg shape also tends to differ from common hosts. The egg is rounder and plumper than the tapered ovals of most songbirds. But again this may not hold true for small hosts laying tiny round eggs.
Egg Color
Cowbird egg color varies regionally:
– Western populations lay white eggs with brown speckles.
– Midwestern eggs are pale bluish-green with darker markings.
– Eastern eggs appear whitish-gray with heavy brown spotting.
So the egg color may stand out against some hosts like robins and catbirds that lay uniform blue eggs. But other hosts like cardinals and thrashers also speckle their eggs, camouflaging the cowbird’s.
Host Species | Host Egg Color | Host Egg Shape |
---|---|---|
American Robin | Pale blue | Elongated oval |
Gray Catbird | Medium blue | Rounded oval |
Northern Cardinal | Off-white with red-brown spots | Short oval |
Reporting Brown-headed Cowbird Sightings
Recording your Brown-headed Cowbird observations through citizen science platforms helps researchers track this species:
eBird
The Cornell Lab of Ornithology’s eBird app allows you to log location, date, photographs, and numbers of Brown-headed Cowbirds and any evidence of parasitism. Records are added to a real-time species database.
iNaturalist
This app connects to a community of naturalists who help identify photographed observations. You can upload images of Brown-headed Cowbirds and their eggs to get confirmation.
NestWatch
For nesting data, Project NestWatch through the Cornell Lab is ideal. If you find a Brown-headed Cowbird egg in a host nest, you can submit nest cards with information like location, egg descriptions, and fate.
Local Audubon
Connect with your local Audubon chapter to learn about any regional monitoring or conservation projects related to Brown-headed Cowbirds you can take part in.
Conclusion
Identifying the sneaky Brown-headed Cowbird takes careful attention to detail when it comes to subtle plumage differences, voices, behaviors, and egg characteristics. But making the effort to detect and report these brood parasites provides valuable data to ornithology projects tracking impacts on host songbird populations. So grab your binoculars and camera and keep an eye out for Brown-headed Cowbirds in your area!