Offered as an unusual observation: sixteen Red-tailed Hawks roosting (roosting in the sense that they were together, not in the overnight sense: the photo was taken at 11 in the morning) together in two trees. More Red-tails were flying in and out. There were a whole whack of American Crows (Corvus brachyrhynchos) just beyond the crest of the hill; you could tell that they were there because as a Red-tail would fly over, some of them would fly off.
Dad was excited in part because he had not seen so many Red-tails together at one time. So, just what were they doing there? In doing the lightest of lit reviews, I found one reference to communal roosting in winter. Charles R. Preston, in the book Red-tailed Hawk, writes that "although red-tails do not usually participate in the large, communal winter roosts typical of Bald Eagles, I have frequently found four to six red-tails roosting together in a small cluster of trees." (p.67)
I also managed to find one peer-reviewed article: Competition between American Crows and Red-Tailed Hawks for a Carcass: Flock Advantage (link) which suggests that Crows have an advantage at a carcass over Red-tails when they’re in large numbers. Since we’re talking a large number of Crows and Red-tails, perhaps the explanation lies in some unseen carcass.
