I photographed these vultures during an after-lunch walk about a week ago near College park, Maryland. When I first saw them circling in the air, I thought there was probably a dead animal nearby that had attracted them. They were near the railroad tracks and so my initial guess was that there was perhaps a dear hit by a train. But a quick look up and down the tracks did not reveal anything resembling a carcass. Nor were there any vultures along the tracks.
Eventually, the birds perched on a pipe of the nearby defunct factory. This was the closest I could get with the small digital camera I had with me.
They are either black vultures (Coragyps atratus) or juvenile turkey vultures (Cathartes aura). I understand the 2 species can be distinguished from their wing patterns seen from below. If I see them again I will try to photograph them flying.