These birds are what they call parasitic. They lay their eggs in other birds nests. l have a little song sparrow that has raised baby cowbirds 2 years in a row. Size difference is incredible. But the song sparrow treats them like there own. At least this year although she had 2 BHC, she did manage to keep and raise one of her own as well. One of the more less popular birds, l still find them quite pretty. And hey,that is how they were made to be. Who are we to judge.