This bird is a brood parasite which means it lays its eggs in the nests of other small passerines (perching birds), particularly those that build cup-like nests. The Brown-headed Cowbird eggs have been documented in nests of at least 220 host species, including hummingbirds and raptors.
So basically, the young cowbird is fed by the host parents at the expense of their own young. Brown-headed Cowbird females can lay 36 eggs in a season. More than 140 different species of birds are known to have raised young cowbirds.
So this is what happens…
A cowbird drops its eggs off in another bird’s nest and once the egg has hatched with the other eggs, the mother bird feeds all the hatchlings. The cowbird chick then eats more than its share, which in turn makes the chick grow faster. Eventually, the chick dominates the nest and takes over as the host. It puzzles scientists that the bird doesn’t just kill their nest mates eventually, because genetically, they don’t benefit from growing up with a species that isn’t their own.
Same story with the Common Cuckoo who is also a brood parasite; it lays its eggs in the nests of other birds. At the appropriate moment, the cuckoo flies down to the host’s nest, pushes one egg out of the nest, lays an egg and flies off. The whole process takes about 10 seconds. A female may visit up to 50 nests during a breeding season. Common Cuckoos first breed at two years old.
Just thought this was interesting and wanted to share!