Last month, I removed an old nest from a box and a few weeks later an egg appeared. Could this be an optimistic cowbird?

Kenn and Kimberly:

lots of brown dots, could have been laid by a brown-headed cowbird, but other kinds of birds have similar eggs. Cowbirds are brood parasites that always lay their eggs in the nests of other species. But usually the female cowbird carefully chooses an active, occupied nest where the egg is sure to be incubated. It’s very unusual for an egg to appear in a vacant nest like this. However, sometimes a female bird is ready to lay an egg and doesn’t have a nest available, so she’ll just dump it somewhere. That could