Cukoo Birds, look it up!
Because it's to hard to fly when you have a bunch of babies kicking around in your gut. They can also jump from side to side and cause a bad in air collision.
Cowbirds lay eggs in nests built by other birds. They are left to be hatched by the other birds.
In North America, cowbirds do this. In Europe, it is a type of Cuckoo that does this.
A Crow???
mostly