|The Mammals of Texas -
Desert Pocket Mouse
Rodentia : Family Heteromyidae
: Chaetodipus penicillatus Woodhouse
Description. A medium-sized pocket mouse
with long, heavily crested, and tufted tail; pelage
coarse, but lacking spines on rump; sole of hind foot
naked to heel; upperparts vinaceous buff finely sprinkled
with black, imparting a grayish tone; sides like back; no
lateral line; underparts and tail to tuft, white.
External measurements average: total length, 205 mm;
tail, 109 mm; hind foot, 25 mm. Weight, 15-23 g. Dental
formula as in Perognathus flavescens.
Distribution in Texas. A southwestern
pocket mouse that, in Texas, occurs mainly in the
Trans-Pecos eastward to Val Verde and Crane counties.
Habits. This species in general
occurs on sandy or soft alluvial soils along stream
bottoms, desert washes, and valleys. In the Big Bend of
Texas, large numbers of them have been trapped in loose
sand along the Rio Grande where the dominant vegetation
was Baccharis and mesquite and also in a brushy
draw where the soil was hard-packed silt. We never found
them on gravelly soils or among rocks, a habitat
preferred by the externally similar Chaetodipus
intermedius. Their burrows,
from which the sand has been thrown well out to one side,
are usually found near the bases of bushes and are closed
in the daytime.
Their habits are not well-known. Like
other pocket mice, they are strictly nocturnal. Their
food consists of seeds; those of mesquite, creosote bush,
and broomweed have been found in their cheek pouches.
Richard Porter found that in the Big
Bend area the breeding season of this pocket mouse began
in late February, the peak of pregnancies among females
was in April, and the peak of juveniles in the population
occurred in May. Lesser peaks of pregnancy occurred in
June and August. The number of embryos per litter
averaged 3.6 with extremes of two and six. Many of the
young females reached sexual maturity early and became
pregnant while still in their juvenile pelage.
The annual population turnover in this
species is high nearly 95%, according to
Porters studies. Consequently, only 5% of the
individuals present at the seasons peak survived 12
months in the wild. Only two juveniles of the 89
live-trapped animals he handled survived more than one
penicillatus is difficult to distinguish from C.
intermedius and C. nelsoni.
Table 3 gives some of the external features useful in
identifying these species. In addition, the size and
position of the interparietal bone in relation to the
mastoid bullae is a most useful character in separating
two of the species. Note in Figure 5 that in penicillatus the interparietal
is separated from the bullae by straplike projections of
the parietals and the supraoccipital, whereas in intermedius
the interparietal is in contact with the bullae or nearly
so. In addition, intermedius has a slightly
narrower rostrum and the dorsal profile of the cranium is
more highly arched.
TABLE 3. External
features used in initial identification of Trans-Pecos Chaetodipus.
ends usually darkly
entire spine lightly
entire spine usually
both dorsally and
but less numerous;
length about same
as rump spines
|Total length of
than 180 mm
than 180 mm
than 180 mm
|Soles of hind feet
Photo credit: R.D.