This it the first time I've photographed a cowbird.
Here's some info about them from the Cornell Lad of Ornithology which will explain their nastiness if you're interested. They're aggressive birds who don't bother to build their own nests, rather they just lay their eggs in the nests of other birds and abandon them, leaving them for the host birds to raise their young. If the host birds do not recognize the cowbird eggs or are too small to get rid of them, the cowbird eggs usually hatch first and develop faster, jeopardizing the hatching and growth of the rightful babies. Cowbirds have different mates over the course of the summer and can lay up to 3 dozen eggs a season. They are known to lay eggs in 220 different species of birds' nests! Usually an individual female with stick with the same species when she chooses her foster parents.
