The Perdido Key beach mouse has a small body, haired tail, relatively large ears, and protuberant eyes. Its head and body length is 2.7 to 3.3 inches; the tail length is 1.7 to 2.5 inches. The upper parts are colored grayish fawn to wood brown with a very pale yellow hue and an indistinct middorsal stripe. The white of the underparts reaches to the lower border of the eyes and ears, and the tail is white to pale grayish brown with no dorsal stripe. This species is a nocturnal herbivore. Beach mice feed primarily on the seeds of sea oats (Panicum repens) and beach grass (Panicum amarums). When these seeds are scarce, especially in the late winter or early spring, beach mice may consume invertebrates (Ehrhart in Layne, 1978) or fruiting bodies of sea rocket (Cakile) sp. (U.S. Fish and Wildlife Service, 1987).