It lives solely on San Esteban Island, an arid volcanic rock in the Gulf of California virtually devoid of permanent fresh water, where it has developed a remarkable tolerance to scarcity of moisture, deriving almost all the water it needs from its food. It shares this tiny island with an exceptionally large endemic lizard, the only member of its genus on the island, turning San Esteban into another of the small laboratories of island evolution so characteristic of the Gulf of California. Its entire population is confined to the few square kilometres of this desert island, with no other known locality in the world. It is yet another example of how island isolation in the Gulf of California has produced, island by island, its own exclusive version of field mouse.
Small rodent with greyish-brown to sandy fur on the back and white on the belly, adapted to the extreme arid conditions of its island. It differs from other Peromyscus species in the Gulf of California by its exclusive distribution on San Esteban Island, with no overlap with any other island or mainland population.
Tracks and signs: small track, 1.3-1.8 cm, showing 4 front toes and 5 hind toes. Small, elongated droppings, 3-5 mm long, left scattered along paths among the island's sparse vegetation. Digs shallow burrows beneath volcanic rocks or roots, with the entrance semi-hidden among the scarce island cover.
Arid scrub on a volcanic desert island, virtually without permanent sources of fresh water, in lowlands. Endemic to San Esteban Island in the Gulf of California, Mexico, with no natural presence outside this island.
Omnivorous, feeding on seeds, leaves and invertebrates from the island's sparse vegetation, obtaining most of its required water directly from its food.
Solitary and nocturnal, with a home range centered on refuges among volcanic rocks and the sparse island vegetation.
Its restriction to a single tiny, arid island, alongside the constant risk of predator introductions, leaves its populations extremely vulnerable.
Risk of introduction of cats, rats or other predators to San Esteban Island, together with the species' extreme geographic restriction to a very small and arid island territory.
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