In early August 2009 I came across three young Brown-headed Cowbirds foraging in a hawthorn tree at the Terra Nova Wildlife Area in Richmond, and I mused about whether or not they could have been reared in the same nest. I remarked that I had previously never seen more than one at a time. In almost exactly the same spot last Friday (Aug. 12, 2011) we found a flock of at least six young cowbirds. They alternated between foraging in the hawthorns and on the gravel path.
Anybody out there know anything about juvenile cowbird flocking behaviour? Are they so habitat-specific that all would inevitably end up in the same place? Or do they find each other through vocalizing or some other means? Cowbird bat-signal?