I found a songbird nest with two different types of eggs in it. What is going on?

If you are in the U.S. or Canada, there is a good chance you’ve discovered a nest with Brown-headed Cowbird eggs in it. Cowbirds don’t build their own nest; instead they lay their eggs in other birds’ nests and their chicks are raised by the host species—a behavior known as brood parasitism. This can be detrimental to the host bird, but like other native birds, cowbirds and their eggs are protected by the Migratory Bird Treaty Act and it is illegal to disturb them. Read more about this interesting species in our online bird guide.