When Dunbar arrives at Ft. Sedgwick, he finds it abandoned and begins looking for signs or clues of its former inhabitants. At one point a bird flies up--apparently to illustrate that the fort has reverted to wilderness. The bird is a Ringed Turtle Dove, a native of North Africa. Today there are a few small populations of the doves in North America formed in the last few decades by escaped cage birds, but you can be sure this would not be the case in the Wild West in the 1860's--unless it was western Libya!