White-ankled Mouse
Order Rodentia : Family Muridae : Peromyscus pectoralis (Osgood)

Description. A small-eared, long-tailed, white-footed mouse with tarsal joint of hind foot white; pelage moderately long and lax; tail longer than head and body, scantily haired, not sharply bicolor, but darker above than below, and annulations 20-24 per cm; upperparts grayish to wood brown; underparts and feet white; young, bluish gray. External measurements average: total length, 187 mm; tail, 95 mm; hind foot, 22 mm; ear, 16 mm. Weight, 24-39 g. Most easily confused with P. eremicus, P. attwateri, and P. boylii. Distinguished from P. eremicus by having proximal part of sole of hind foot hairy rather than naked; mammae in three pairs rather than in two. Differs from P. boylii and P. attwateri in smaller scales on the tail, and in white, rather than dusky, tarsal joints and in shorter maxillary tooth row (often less than 4 mm).

Distribution in Texas. Recorded from most of Trans-Pecos region and northeastward through central part of state to Oklahoma (eastern limits of range along Balcones Escarpment from Bexar County northward to McLennan County).

Habits. This is another rock-dwelling species, and it often is taken in the same habitat occupied by P. boylii. In the Chisos Mountains and again in the Delaware Mountains in Trans-Pecos Texas, they have been caught in the oak-juniper belt in traps set among jumbled boulders, near rock walls, in talus slopes, along rocky outcroppings, and in buildings. Near Austin, white-ankled mice are common in the rocky outcropping where the Colorado River cuts through the Balcones Escarpment; in Kerr County they prefer rocky bluffs along the rivers and creeks. In the Davis Mountains region of Trans-Pecos Texas, they usually are found in the grama-bluestem association. Elsewhere, in our experience, they are associated with rocks in oak-juniper woodlands.

They feed on a variety of seeds, including juniper berries, acorns, and hackberries. Although their diet has not been studied in detail, other seeds, some fruits, and insects probably are taken when available. They readily come to traps baited with rolled oats.

Their breeding habits are not well-known, but the breeding season extends at least from March to October. Pregnant females have been captured in March, April, May, July, August, September, and October, which suggests that several litters may be reared each year. The average litter size is three, ranging from two to five. The gestation period has not been determined, but it is probably about 23 days as in closely related species. Growth and development of the young is not well known.

These mice are abundant in certain localities and may become troublesome in cabins and ranch buildings. They usually can be controlled easily by the use of traps or poisoned grains.

Photo credit: John L. Tveten.