We were in Quakertown, PA on June 21st when I saw an unusual sighting (for me, anyway). In preparing to make this post, I may have answered my own question! I saw a bird moving around and saw that it was a chipping sparrow. It was being followed by a considerably larger bird that was very nondescript and gray in colour. (It was a cloudy day and the setting was in a heavily-treed trailer park with lots of hills and valleys.) I sensed that there were light bars on the wings perhaps, the bird walked (as opposed to hopping) and there were faint stripes on the breast. I could not really see an eye ring but something seemed light in the eye area. If the chipping sparrow flew onto a rock, the other bird did as well. It seemed to keep it's head low as it walked. In my mind it was about the size of a cowbird (so I just now checked in Sibley's - earlier having thought some sort of a thrush) and realized that a juvie cowbird looks very much like the bird I saw. Then I remembered that cowbirds lay their eggs in other birds' nests. Would I have been witnessing a young cowbird hatched in a chipping bird nest? Or is there some other explanation for this unusual behavior?
Also, just wanted to say that I was surprised how many different birds I saw in that backyard: tufted titmouse (3), lots of downys, a catbird, chickadees and a bluebird pair (amongst the regular stuff). That one surprised me because I didn't expect bluebirds in that setting, although there are open areas nearby.
