Female Cowbird: Notorious Nest Invaders

A female cowbird is a dull looking bird with plain plumage that is easy to miss in the backyard. But there's a really important reason for that.

How to Identify a Female Cowbird

Female brown-headed cowbird at feederCourtesy Christal Knight
Female cowbird on a seed feeder

Question: “I’ve lived in this house for 20 years and I’ve never seen this bird before. What could my new yard bird be?” asks Christal Knight of Palatka, Florida.

Kenn and Kimberly: One of the most subtly colored birds in North America, lacking any distinctive pattern, the female brown-headed cowbird is a frequent source of confusion for birders. It’s easy to overlook, too. The female cowbirds have a good reason to be inconspicuous: They lay their eggs in the nests of other birds, sneaking in quietly while the nests’ owners aren’t looking.

A female cowbird is easiest to see when they come to a feeder, as in your photo. The short, thick, pointed black bill ending at a flat forehead and overall plain, dull grayish-brown look are the best field marks for recognizing them.

Male brown-headed cowbirds are more noisy and noticeable.

Check out 5 types of blackbirds you should know.

Female Cowbirds Don’t Build Their Own Nests

juvenile cowbirdCourtesy Julia Worth
Chipping sparrow feeding a young cowbird

Female cowbirds are brood parasites. They don’t build nests or tend to their own young. Rather, they employ what seems to be an unfair strategy of laying eggs in the nests of other birds, such as the chipping sparrow. The adoptive adults hatch the cowbird eggs, unaware they aren’t the biological parents. These unwitting foster bird parents then care and feed the young cowbirds.

Female brown-headed cowbirds sometimes produce more than 24 eggs in a single summer. Cowbird eggs have been found in nests of more than 220 other species.

Take a quiz to see how many female birds you can identify.

Female Brown-headed Cowbird femaleStan Tekiela Author / Naturalist / Wildlife Photographer/Getty Images
The female brown-headed cowbird is a plain bird without any distinctive markings

It can be tough to see a small songbird feeding the much larger young cowbird, but it’s very important not to interfere. Cowbirds are a native species, protected by law. They do create conservation challenges for some species, such as Kirtland’s warbler, but in general nature manages to maintain a fair balance.

Although cowbirds are a parasitic pain for bird parents, some birds have figured out ways to successfully deal with them. Catbirds, for example, usually recognize their own eggs and toss out any interloper eggs they find in their nests.

Learn how to keep house sparrow nests out of bluebird boxes.

Cowbird Eggs

12 Bbam23 Lindsayarnold2Courtesy Lindsay Arnold
Cowbird eggs in a house finch nest

Question: “A nest on my wreath had three small blue eggs. The next day I checked and saw four spotted brown eggs in there too. What’s going on?” asks Lindsay Arnold of Stillwater, Minnesota.

Kenn and Kimberly: A house finch built the nest—for some reason, house finches seem to like nesting in hanging wreaths more than any other bird in the eastern U.S. A female house finch laid the three blue eggs, probably one per day over the space of three days.

But the spotted brown eggs are those of brown-headed cowbirds, which are brood parasites that always lay their eggs in nests of other birds, leaving the foster parents to hatch the eggs and raise the young. If the four cowbird eggs all appeared in one day, they were probably laid by four different female cowbirds.

Learn how to identify bird eggs by color and size.

Cowbird Fledglings

13 Askexperts Bbjj23 Marianneraft1Courtesy Marianne Raft

Question: “What are these birds at my reflecting pool?” asks Marianne Raft of Loudon, Tennessee.

Kenn and Kimberly: You’ve captured a dramatic behavior involving two species: an adult song sparrow caring for a young brown-headed cowbird that has just left the nest. Cowbirds always lay their eggs in the nests of other bird species, leaving the unwitting adoptive parents to hatch the eggs and feed their young. In the eastern states, song sparrows are among their frequent hosts. The young cowbird will grow up to weigh twice as much as the foster parents that are hurrying to keep it fed now. It may seem unfair to the sparrows, but cowbirds are a native species, protected by law, and we shouldn’t intervene.

What is a fledgling? See how a baby bird grows up.

Kenn and Kimberly Kaufman
Kenn and Kimberly are the official Birds & Blooms bird experts. They are the duo behind the Kaufman Field Guide series. They speak and lead bird trips all over the world. When they're not traveling, they enjoy watching birds and other wildlife in their Northwest Ohio backyard. Fascinated with the natural world since the age of 6, Kenn has traveled to observe birds on all seven continents, and has authored or coauthored 14 books about birds and nature, including include seven titles in his own series, Kaufman Field Guides, designed to encourage beginners by making the first steps in nature study as easy as possible. His next book, The Birds That Audubon Missed, is scheduled to be published by Simon & Schuster in May 2024. Kenn is a Fellow of the American Ornithological Society, and has received the American Birding Association’s lifetime achievement award twice. Kimberly is the Executive Director of Black Swamp Bird Observatory (BSBO) in northwest Ohio. She became the Education Director in 2005 and Executive Director in 2009. As the Education Director, Kimberly played a key role in building BSBO’s school programs, as well as the highly successful Ohio Young Birders Club, a group for teenagers that has served as a model for youth birding programs. Kimberly is also the co-founder of The Biggest Week In American Birding, the largest birding festival in the U.S. Under Kimberly’s leadership, BSBO developed a birding tourism season in northwest Ohio that brings an annual economic impact of more than $40 million to the local economy. She is a contributing editor to Birds & Blooms Magazine, and coauthor of the Kaufman Field Guides to Nature of New England and Nature of the Midwest. Accolades to her credit include the Chandler Robbins Award, given by the American Birding Association to an individual who has made significant contributions to education and/or bird conservation. In 2017, she received a prestigious Milestone Award from the Toledo Area YWCA. Kimberly serves on the boards of Shores and Islands Ohio and the American Bird Conservancy.