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  The Mammals of Texas - Online Edition

Nelson's Pocket Mouse
Order Rodentia : Family Heteromyidae : Chaetodipus nelsoni Merriam

Nelson's Pocket Mouse (Chaetodipus nelsoni).  Photo by R.D. Porter.Description. A medium-sized pocket mouse with harsh pelage and numerous black-tipped spines on rump; tail longer than head and body, sparsely haired on basal half, the terminal half crested, penicillate, and indistinctly bicolor, darker above than below; upperparts drab gray, heavily lined with black; underparts pure white; soles of hind feet blackish. External measurements average: total length, 187 mm; tail, 104 mm; hind foot, 22 mm. Weight, 14-17 g. Dental formula as in Perognathus flavescens.

Species distribution mapDistribution in Texas. A Mexican form that occurs in Texas in the southern and central Trans-Pecos region and just east of the Pecos and Rio Grande Rivers.

Habits. This is a rock-loving species. In the Big Bend section of Texas, it occurs most commonly at the base of the Chisos Mountains at altitudes ranging from 700 to 1,450 m. There it is found in rocky areas supporting sparse stands of Chino grass, sotol, bear grass (Nolina), and candelilla; sandy washes seem to be avoided.

In the Big Bend region, Richard Porter found that the breeding season begins in February, the peak of pregnancy among females is reached in March, and juveniles entered his live traps in April. By inference, therefore, the gestation period is about 1 month and the young leave the nest when about 4 weeks of age. Pregnant females were captured in each month from March through July. The number of embryos per litter averaged 3.2 with extremes of two and four.

The annual turnover in the population he studied was about 86%; that is, only 14 of each 100 individuals survived from one year to the next. Keith Dixon, working on the Black Gap in the Big Bend, recorded two individuals marked as juveniles that survived for at least 30 months in the wild — one other for 24 months and two others for about 20 months.

Porter reported that nelsoni was more active in winter (December) than either of the other two pocket mice (Perognathus flavus and C. penicillatus) on his study area. Seemingly, nelsoni does not hibernate.

Photo credit: R.D. Porter.