Texas Mouse
Order Rodentia : Family Muridae : Peromyscus attwateri J.A. Allen

Description. A medium-sized Peromyscus with the tail about as long as (or slightly longer than) the head and body, moderately haired, darker above than below (but not sharply bicolor) and usually with a terminal tuft; hind foot large (24-27 mm); ankles usually dark or dusky; dorsal color near sayal brown, darker and mixed with blackish along midline; sides pinkish cinnamon; ventral color pure white, the bases of the hairs plumbeous; length of maxillary tooth row 4 mm or more; each large upper and lower molar has an accessory loph (see Figure 6). External measurements average: total length, 198 mm; tail, 103 mm; hind foot, 25 mm. Weight of adults, 25-35 g.

Distribution in Texas. Occurs in central part of state southward to Uvalde, Medina, and Bexar counties.

Habits. P. attwateri inhabits the cliffs and rocky outcrops of the Edwards Plateau, the West Cross Timbers, the Rolling Plains, and the escarpment of the Llano Estacado in Texas. Vernon Bailey recorded that in the vicinity of Kerrville he caught many of them in traps set in crevices along the cliffs, under logs in the woods, and under fallen grass and weeds on a creek bank in the bottom of a gulch, as well as under heaps of driftwood. They seem to prefer rocky areas where the dominant vegetation is juniper. They are adept at climbing. Charles Long recorded that, when compared with other species of Peromyscus, P. attwateri is a superior and more cautious climber, seldom jumps from high places when under stress, and is more capable of finding its way in darkness. Recent studies using tagged P. attwateri have shown that this mouse, at least in some areas, is semi-arboreal and travels frequently in trees.

Where P. attwateri and P. pectoralis co-exist, P. pectoralis specializes in areas of rock ledges and leaf litter, whereas P. attwateri is more of a habitat generalist and may be found not only in areas of rock ledges and leaf litter but also more open, grassy areas with only scattered rock cover.

Their main diet is plant material, especially seeds. In southern Missouri, Larry Brown found that about 70% (by volume) of the stomach contents he examined consisted of plant material, including fragments of seeds, berries, bulbs, and green plants. The balance consisted of insects, chiefly camel crickets and beetles.

In an ecological study of this mouse in Lynn County, Texas, Herschel Garner found that reproductive activity began in late September and continued throughout the winter. He found no evidence of their breeding during late spring and summer. The number of young per litter varies from one to six and averages about four. Based on data derived from the retrapping of marked animals, Larry Brown estimated the average lifespan to be 6.8 months with a maximum of 18 months.

Remarks. Peromyscus attwateri was formerly treated as a subspecies of P. boylii until one of us (Schmidly) removed attwateri and returned it to its original status as a full species. This taxonomic change was based primarily on characteristics of the karyotype (attwateri has six large biarmed autosomal chromosomes compared to only two in boylii from west Texas). In addition to chromosomal differences, the most useful morphological features available in the field, and to those not trained in cytogenetics, that separate P. attwateri from P. boylii are: (1) larger hind foot (24-27 mm in attwateri and 20-23 mm in Texas-taken boylii) and (2) the structure of the molar teeth. In attwateri an accessory loph is present in both the upper and lower molars, but that structure is absent from the lower molars of boylii (see Figure 6).