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Female brown-headed cowbirds are brood parasites who famously outsource parenting to other bird species. Skipping nest-building and caretaking, the mother can lay up to 40 eggs and hide them in several other birds’ nests, sometimes putting the other eggs at risk. It’s a common question for birders who see a nest with two different colored eggs inside. What should you do if you see cowbird eggs?
Two Different Colored Eggs in Nest
“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 Birds & Blooms reader Lindsay Arnold from Stillwater, Minnesota.
Birding experts Kenn and Kimberly Kaufman say, “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.”
Should You Remove Cowbird Eggs?
If you see cowbird eggs in a bird nest, you should not remove them or take any action at all. Kenn and Kimberly say, “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, but cowbirds are a native species, protected by law, and we shouldn’t intervene.”
Can you move a bird nest near your home?
Cowbird Eggs in Eastern Phoebe Nest
“My shed was left open and I saw an eastern phoebe slipping out. Inside was a nest with four white eggs and two speckled eggs. What kind of bird lays eggs and leaves them in another nest?” asks reader Patricia Bourgeois of Douglas, Massachusetts.
Kenn and Kimberly say, “The four white eggs in your photo were laid by the phoebe, but a female brown-headed cowbird is responsible for the two speckled eggs. Cowbirds are brood parasites and never raise their own young. Instead, they lay their eggs in the nests of other songbirds, leaving the unwitting foster parents to hatch the eggs and feed the young. Eastern phoebes build open nests that are easy to find, so they are frequent targets for cowbirds. In some parts of their range, as many as one in four phoebe nests contains cowbird eggs.”
About the Experts
Kenn and Kimberly Kaufman are the official bird experts for Birds & Blooms. They are the creators of the Kaufman Field Guide series and they lead birding trips all over the world.
