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Molothrus Ater - Blog Posts
Brown-headed Cowbird (Molothrus ater), juvenile, being fed by a Song Sparrow (Melospiza melodia), taken May 9, 2025, in Georgia, US
A fat cowbird chick being fed by its song sparrow foster parent! It seems as though our only song sparrow pair were chosen by the cowbirds as fosters this spring. Luckily, song sparrows are known to attempt to nest up to four times in a season, so they have plenty of chances left to raise their own brood! Once this baby cowbird becomes independent, it will meet with other baby cowbirds and begin its life as a young adult! For now, though, it's content to take handouts from mom and dad!
I feel as though the concept is much more common knowledge now, but to those who come across this and don't know: cowbirds are nest parasites, meaning they lay their eggs in the nests of other birds so they don't have to raise their babies themselves. They do this because building a nest and caring for young is extremely costly for females and may result in a lower chick yield than creating more eggs (up to 40) and laying them in an array of host nests does. The cowbird chick often hatches before the host nest's chicks, grows faster, becomes larger, and is louder, leading to the host chicks being neglected and often dying before fledging. While this is sad, bird parents have evolved to account for the possibility of being parasitized and will often nest multiple times in a season to ensure they have at least one healthy brood of their own chicks! Many bird species are also extremely good at recognizing cowbird eggs and can either eject them from the nest or destroy them before they hatch. Nest parasites are one of many natural population control agents that ensure native bird populations remain stable, so they are not a bad thing if the parasite is native, which cowbirds are in the US!
Brown-headed Cowbird (Molothrus ater), juvenile, taken May 27, 2024, in Georgia, US
Fledgeling season is so fun when there's a bird bath because you get to see baby birds have pool parties! This particular individual injured its leg in some way and lived exclusively at our feeders for weeks, eating seeds off the ground and begging for handouts from any adult bird who got close lol. Surprisingly, it didn't get picked off and its leg ended up healing, so we got to see it reach adulthood with its siblings!