OCTOBER 1989 - City of Boulder

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MEXICAN WOODRAT
~istribution-The Mexican woodrat is a species of the Mexican
Plateau and southwestern United States. 1t.reaches its northern
limits in Larimer County, Colorado. In the Boulder area it occurs in
the foothills, in suitable habitat throughout the Boulder Mountain
Parks. Specimens have been reported from the following localities:
Skunk Canyon; base of Flagstaff Mountain; Gregory Canyon; Boulder
Canyon; Bluebell Canyon. The type locality of the local subspecies,
Neotma rneacana fallax, is Gold Hill.
Description--Mexican woodrats are dirty grayish brovn above and
whitish below. The long, slender tail is obviously bicolored. They
are smaller in size than the bushy-tailed woodrat, and the tail is not
so fully haired.
Mean (and extreme) external measurements of eight males, followed
by those of six females, from Larimer and Boulder counties, are: total
length, 337.9 (313-361),.321.4 (303-334); length of tail, 153.8 (144-
167), 141.7 (132-150); length of hind foot, 34.2 (33-36), 32 (20-24).
A male weighed about 150 gr. Condylobasal length of 10 males and eight
females was 42 -68 (41., 7-45-31. 41.83 (40.5-4.3.6) ; zygomatic breadth was
23.42 (22.3-24,6), 22.67 (21.8-23.5).
Natural History-The Mexican woodrat is a fairly common resident of
the broken, rocky areas of the foothills. The character of the rock
outcrops is a mre important feature of habitat than is vegetation.
Mostly these rats -1ive'i.n and among boulders and beneath shelves of
sedimentary rock. There they build characteristic stick dens, festooned
with whatever other material is at hand, including castoffs from
civilization: paper, woodscraps, tin cans, bottle caps, and so forth.
Within the den is a nest, usually linedwith soft plant fibers, and
nearby there will be a food supply.
The diet consists mostly of foliage of forbs and shrubs. Vegeta-
tion is stored in and around the den. Some cactus is eaten, although
less in this species than some more southern kinds. Typical food plants
in our area are skunkbush and mountain mahogany, although needles of
conifers may be eaten. The animals are active throughout the year,
feeding on food stored up in autumn.
The breeding season begins in March. Two to five young are born
in April after a gestation period of about 30 days. Apparently, there
is a postpartum estrus. Most females produce two litters per year..
By autumn the young disperse to set up housekeeping on their own.
Probably, most individuals are able to take over and rennovate some
abandoned den. Uoodrats without proper den sites are vulnerable to
both predators ad to physical extremes.
Predators include coyotes, bobcats, snakes and owls. Woodrats
harbor a variety of parasites, including fleas and parasitic worms
of various kinds.
Selected references-Armstrong (1982) ; Brown (1969); Finley (1958).
D.M.A.