||The Mammals of Texas -
Northern Pygmy Mouse
Rodentia : Family Muridae : Baiomys
Description. Smallest of the muroid mice
in Texas, with the exception of two harvest mice, Reithrodontomys
humulis and Reithrodontomys
montanus, both of which
differ in having grooved upper incisors and longer tail.
Upperparts grizzled grayish in adults, blackish in
juveniles; underparts smoke gray; tail about three times
as long as hind foot, sparsely haired and decidedly
shorter than head and body. They have a strong, musky
odor similar to that of house mice, Mus
musculus. External measurements average: total
length, 98 mm; tail, 38 mm; hind foot, 14.5 mm. Weight,
7-10 g, averaging 8 g.
Distribution in Texas. Distributed over
the central portions of the state; range excludes
Trans-Pecos and eastern Texas. This species is extending
its range northward and westward.
Habits. This is a southern
species, characteristic of the tropical lowlands of
Mexico, that reaches its northern distributional limits
in Texas. Early records indicate that B. taylori
was restricted to the coastal region of eastern Texas and
the mesquite-chaparral regions of southern Texas. Since
the early twentieth century, the species has consistently
extended its range northward and eastward by invading the
oak-hickory association, the blackland prairies, the
cross-timbers, rolling plains, and the high plains.
These mice have a preference for grassy
areas, and they are commonly found in old fields,
pastures, and along railroad and highway rights-of-way,
where they usually live in close association with cotton rats (Sigmodon hispidus) and harvest mice (Reithrodontomys spp.). If other types
of ground cover such as rocks, cactus, and fallen logs
are available, the pygmy mouse may be found in areas
where grass is relatively sparse.
Pygmy mice live in nests placed in
burrows in the ground, beneath fallen logs, among cactus
pads, or in thick clumps of grass. The nest is typically
a ball of finely shredded grass or cactus fibers with a
central cavity and one or two openings. A network of
runways or beaten paths leads away from the nest sites
beneath the thick mat of dead grass.
The mice feed chiefly on vegetation;
seeds are especially well-liked. They are active the year
round and do not hibernate; neither do they store food
for winter use. Although they are chiefly nocturnal, they
have been caught in traps on several occasions in the
daytime. They can swim well when necessary, but water is
avoided whenever possible because their short fur is
The breeding season is nearly year-long
gravid females have been taken from January to
October. In captivity, one female gave birth to nine
litters in 195 days; another, to eight litters in 221
days. The gestation period is about 20 days. The litters
vary in size from one to five, averaging about three. At
birth the young are naked, blind, and helpless and weigh
about 1 g each. The eyes open in 12-15 days; the mice are
weaned in 18-22 days; and sexual maturity is attained at
the age of about 60 days.
Photo credit: R.D.