For decades it was confused with the widespread Western Harvest Mouse (R. megalotis), with which it shares a large part of its range in north-western Mexico, until chromosomal and genetic studies confirmed that it is a separate species, tied to high-altitude grasslands in the Sierra Madre Occidental. It lives in a very specific habitat type: open grassland clearings within pine-oak forest, between 1800 and 2600 m, a mosaic that depends on the natural fire regime of these mountains.
A medium-sized harvest mouse, with head-body 61-70 mm, tail 67-87 mm (longer than the body) and weighing 9-13 g. The back is reddish-brown, with a dark line along the spine. Easily confused with R. megalotis, with which it coexists in part of its range; reliable separation between the two species relies on chromosomal or genetic studies, not on external appearance.
Like the rest of the genus, it is too small to leave recognisable tracks and signs in the field; it builds spherical nests of plant fibre in the grassland clearings it occupies within pine-oak forest.
Open grassland clearings within pine-oak forests of the Sierra Madre Occidental, between 1800 and 2600 m, from western Chihuahua to central-western Michoacán (Mexico).
Feeds on grass seeds and insects, similarly to other species of the genus in grassland habitats.
Nocturnal; its reproductive pattern and activity are presumed to be similar to those of R. megalotis, although not specifically documented for the Zacatecan Harvest Mouse.
Species with a range restricted to the Sierra Madre Occidental, but with no evidence of a documented overall decline.
Loss of mountain grassland clearings through natural fire suppression or land-use change in the mountains.
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