The Zempoaltepec Deermouse lives on the slopes of a single mountain massif, Zempoaltépec, in the heart of the Sierra Mixe of Oaxaca, from which it takes its common name. No other population is known anywhere in the world. Like the rest of its genus, it is an essentially arboreal rodent that moves through the dense undergrowth of cloud forest, aided by a long, prehensile tail much longer than its body. Its discovery and description as a distinct species, separate from other similar-looking Mesoamerican climbing mice, is relatively recent. Much of its basic biology is still to be documented in detail. Its extreme restriction to a single mountain places it among Mexican rodents with the most restricted geographical distribution in the entire country.
A small rodent with greyish-brown fur on the back, paler on the belly, large prominent eyes, well-developed ears, and a long prehensile tail that exceeds its body length. It can be confused with other arboreal mouse species of the same genus from the Oaxaca mountains. Reliable separation requires genetic or cranial analysis; its exclusive origin from the Zempoaltépec massif is the most useful reference for identification.
Small track, 1.5-2 cm, with 4 fore toes and 5 hind toes, rarely visible given its climbing habit. Small, elongated droppings, 4-6 mm long, left scattered through low vegetation and the elevated leaf litter of the undergrowth. It builds spherical nests of grass and moss among dense vegetation or in tree hollows, above ground level. These are typical of the cloud forest where it lives.
Mountain cloud forest, with dense undergrowth and abundant epiphytic vegetation, generally above 2500 m altitude. Endemic to the Zempoaltépec massif, in the Sierra Mixe of Oaxaca, southern Mexico, with no known presence on any other mountain.
Omnivorous, it feeds on seeds, fruits, fungi, and invertebrates from the undergrowth, also utilising resources available among elevated epiphytic vegetation.
The Zempoaltepec Deermouse is arboreal and scansorial, moving with the aid of its prehensile tail among low and high undergrowth vegetation. It is probably nocturnal, and its solitary behaviour is poorly documented due to the scarcity of studies on the species.
Restricted to a single mountain, and facing continued loss of the cloud forest that covers it, Zempoaltepec Deermouse populations are in continuous decline with very limited recovery prospects.
Deforestation and fragmentation of the cloud forest of the Zempoaltepec massif due to agricultural and livestock expansion, and the extreme geographical restriction of the species to a single mountain.
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