Once they followed Bison eating insects kicked up by the herd. Because they were always on the move, they had to lay their eggs in other birds’ nests and hope for the best. Today the herds are gone and they are called Cowbirds and are quite stationary. It’s a fortunate nest in this area that doesn’t sport a Cowbird egg among its own. The problem is so great that an organization exists to make rounds of Bluebird nesting boxes and throw out the offending eggs.
They are handsome. Cowbird pair. Female. This is a House Finch nest. Care to guess which egg was deposited by a Cowbird interloper? Another clue, besides color, is that House Finches, like Robins, almost always lay just four eggs.