Mexican Spiny Pocket Mouse
Order Rodentia : Family Heteromyidae : Liomys irroratus (Gray)

Description. A medium-sized mouse with extremely harsh pelage over entire upperparts (the hairs flattened, sharp-pointed and grooved); external, furlined cheek pouches; and relatively long tail. Similar in general appearance to the spiny-haired pocket mice (Chaetodipus), but upper incisors lack the longitudinal groove on the outer face and the pelage is much more spiny and harsh. Tail about as long as head and body, sparsely haired and distinctly bicolor, brownish above, whitish below; upperparts dark gray, grizzled with orange; underparts pure white; sole of proximal half of hind foot hairy, blackish. External measurements average: total length, 237 mm; tail, 122 mm; hind foot, 30 mm. Weight: males, 50-60 g; females, 35-50 g. Dental formula as in Perognathus flavescens.

Distribution in Texas. A Mexican form reaching the United States in extreme South Texas.

Habits. In southern Texas they live in the densest brush on the ridges forming the old banks of the Rio Grande, along oxbows, and in the scattered remnants of the subtropical palm forests of the Rio Grande near Brownsville (Cameron County). They are often closely associated with thickets of prickly pear. In northern Mexico, they may be trapped among dense chaparral but in the valley of Mexico they occurred around stone fences and among rocks on the sides of mountain slopes. They live in burrows and sometimes throw up small mounds to close the entrances. Usually the openings are covered by vegetation or dead leaves. They are strictly nocturnal.

In southern Texas, they feed on the seeds of hackberry, mesquite, and various other shrubs. In addition, seeds of various weeds may be found in their cheek pouches.

Very little is known about their breeding habits. In Mexico, half-grown young have been found in June and nearly full-grown young in August. None of the females captured in summer was pregnant or lactating. Based on the study of a large number of Mexican records, Theodore Fleming reported immature individuals of Liomys irroratus from all months except May; he believed that breeding occurs throughout the year but with most of it concentrated in the winter period from November to February. Litter size is two to eight, averaging about four.

Photo credit: John L. Tveten.