UPDATE ON 2 SEPTEMBER 2025: A study published in ScienceDirect in August 2025 conducted DNA tests on groups of immature cowbirds and adults captured together and found that the youngsters responded to sounds made by females, always hung out with females (not males), but never hung out with either parent. This article was originally inaccurate; corrections have been made below.
21 June 2012
For weeks I thought that all the brown-headed cowbirds had left Schenley Park, that the females had dumped their eggs in other species’ nests and moved on. But I was wrong.
The cowbirds arrived in mid-April and immediately made themselves noticeable. Males called from the treetops and as many as three puffed and courted a single female. I felt bad for the song sparrows, their most likely victims in Schenley Park, who would be forced to foster those cowbird eggs-in-the-making.
The cowbirds mated, the females dumped their eggs, and then they disappeared. Or so I thought.
As expected, in late May I saw and heard cowbird fledglings begging from song sparrow parents.
In early June I was surprised to hear male cowbirds singing again. According to the literature they’d never left but had spent the intervening weeks monitoring host nests and laying more eggs.
By now the young cowbirds are self-sufficient but they were raised in a song sparrow world. It’s time for them to learn how to be cowbirds. Their parents are oblivious while their mothers lay more eggs and their fathers court females. The youngsters pay attention to female sounds and will start to hang out with adult females they aren’t related to.
Read more about how they learn in this 2025 article: How Do Young Cowbirds Learn To Be Cowbirds?
p.s. See Meredith Lombard’s photo of a chipping sparrow foster parent feeding a cowbird fledgling and a Louisiana waterthrush with its baby cowbird. Notice that the foster parent is smaller than the baby. 🙁
It’s such a shame that they are a parasitic species (I think that’s the term) … their song is so pretty
I was dismayed to see a song sparrow feeding a cowbird chick in my yard this spring. When I first discovered these birds years ago, I tried to learn as much as I could about them. One thing still puzzles me: “City” cowbirds don’t have to follow a herd of cows to eat the insects the cows kick up, so why hasn’t their behavior changed – why don’t they stay and raise their own chicks?
It turns out that cowbirds couldn’t raise their own chicks if they wanted to. They don’t form a brood patch — the bare skin area that allows direct (heated) contact with the eggs — even though they have normal levels of the hormone that induces a brood patch in related species. (factlet from Birds of North America Online)
Thanks for the answer, Kate.
how large are they? I think I had a cowbird on my balcony just a half an hour ago, but it took off before I could take a picture. (July 4 2012)
They are larger than sparrows, smaller than robins. Their head shape & beaks look more like sparrows’ than robins’.