the chimney swift has large, deep set eyes. these are protected by small patches of coarse, black, bristly feathers, which are located in front of each eye. the swift can change the angle of these feathers, which may help to reduce glare. it is far-sighted and, like some birds of prey, this swift is bifoveal: each eye having both a temporal and a central fovea. these are small depressions in the retina where visual acuity is highest, and help to make its vision especially acute. like most vertebrates, it is able to focus both eyes at once; however, it is also able to focus a single eye independently.