A recent post by Jeffrey M Harris described a black-capped chickadee feeding a nest of robins. There has been some follow-up discussion. While not as unusual of the chickadee and robins, I posted some photos of a common yellowthroat feeding a brown-headed cowbird here:
http://www.jimblockphoto.com/2012/05/yellowthroat-feeding-cowbird/
Jim Block
Etna, NH