Cowbirds are brood parasites. They are unable to make their own nests so they lay eggs in other birds nests. They tend to hatch earlier than the hosts, grow faster and so get the lions share of the food. They are very detrimental to endangered warblers. We try to keep and eye on our nests to see what is going on. This is inside the bluebird house where a cowbird egg is clearly visible. Needless to say That egg is history!
Cowbirds are like our British cuckoos. They have the same habit of laying their eggs in other birds nests - usually warblers. When the young hatch they push out all the other eggs/chicks so that the 'parent' birds feed only them.
Yep that's the cuckoo's behaviour alright. Never heard of Cowbirds before Bethie, I've dug up a slideshow: [flickr]cowbird[/flickr]
