It lives solely on Cerralvo, a small island in the Gulf of California, where it has evolved isolated from the rest of its mainland congeners over thousands of generations. As with many island mammals, this geographic confinement has made Dickey's Deermouse an extremely vulnerable species: its entire global population fits within the boundaries of a single desert island off the coast of Baja California Sur. It takes refuge among the arid scrub vegetation and rocks of this island, an ecosystem so small that any local disturbance could impact the whole species at once. Its name honours an American naturalist who documented much of the fauna of the Gulf of California islands in the early 20th century.
A small rodent with greyish-brown fur on the upperparts and white on the belly, large eyes and well-developed ears, like the rest of the mice in its genus. It is distinguished from other *Peromyscus* species in the Gulf of California by its exclusive distribution on Cerralvo Island, with no overlap with any other island or mainland population.
Small track, 1.3-1.8 cm, showing 4 fore toes and 5 hind toes. Small, elongated droppings 3-5 mm long, left scattered along surface runways through the island's arid scrub vegetation. It digs shallow burrows under rocks or roots, with the entrance semi-concealed among the dense vegetation typical of the island's arid scrub where Dickey's Deermouse lives.
Arid desert island scrub, in lowlands. Endemic to Cerralvo Island, in the Gulf of California, Mexico, with no natural presence outside this island.
Omnivorous, it feeds on seeds, leaves and invertebrates from the arid scrubland of the island it inhabits.
Solitary and nocturnal, with a home range centred on shelters among rocks and dense vegetation on the island where it lives.
Its restriction to a single small island, together with the constant risk of predator introductions, leaves its populations extremely vulnerable, a situation aggravated in recent years by assessments indicating a continued decline.
Risk of introducing cats, rats or other predators to Cerralvo Island, alongside the extreme geographical restriction of Dickey's Deermouse to a very small island territory.
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