Life History of the Kangaroo Rat | Page 4

blackish about halfway between base and tip, and with two lateral side
stripes of white to a point about halfway back; tail tipped with pure
white for about 40 millimeters (Pl. I). Underparts white, hairs white to
bases, with some plumbeous and buffy hairs about base of tail; fore
legs and fore feet white all around; hind legs like back, brown above,
hairs with gray bases, becoming blackish (fuscous-black or
chætura-black) about ankles, hairs on under side white to bases; hind
feet white above, dark-brown or blackish (near fuscous) below.
Color variations in a series of 12 specimens from the type locality and
points widely scattered through the range of spectabilis consist in
minor modifications of the degree of coloration, length of white tip of
tail, and length of white lateral tail stripes. In general the color pattern
and characters are remarkably uniform. Young specimens, while
exhibiting the color pattern and general color of adults, are
conspicuously less brown, and more grayish.
There appears to be little variation in color with season. In the series at
hand, most specimens taken during the fall, winter, and spring are very
slightly browner than those of summer, suggesting that the fresh pelage
following the fall molt is a little brighter than is the pelage after being
worn all winter and into the following summer. But at most the
difference is slight.
OIL GLAND.
Upon separating the hairs of the middle region of the back about a third
of the distance between the ears and the rump, one uncovers a
prominent gland, elliptical in outline, with long axis longitudinal and
about 9 millimeters in length. The gland presents a roughened and
granular appearance, and fewer hairs grow upon it than elsewhere on
the back. The hairs in the vicinity are frequently matted, as if with a
secretion. In worn stage of pelage the gland may be visible from above

without separating the hairs. Bailey has suggested that this functions as
an oil gland for dressing the fur, and our observations bear out this
view. Kangaroo rats kept in captivity without earth or sand soon come
to have a bedraggled appearance, as if the pelage were moist. When
supplied with fine, dusty sand, they soon recover their normal sleek
appearance. Apparently the former condition is due to an excess of oil,
the latter to the absorption of the excess in a dust bath. The oil is
doubtless an important adjunct to the preservation of the skin and hair
amid the dusty surroundings in which the animal lives.
MEASUREMENTS AND WEIGHTS.
External measurements include: Total length, from tip of nose to tip of
tail without hairs, measured before skinning; tail vertebræ, length of
tail from point in angle when tail is bent at right angles to body to tip of
tail without hairs; and hind foot, from heel to tip of longest claw.
The following are measurements of a series from the U. S. Range
Reserve:
[Transcriber note: Next line was corrected per erratum. The original
text was of the following paragraph (_Averages for 17 adult females:
Total length, 326.4 millimeters_).]
Average measurements of 30 adult specimens of both sexes: Total
length, 326.2 millimeters (349-310); tail vertebræ, 188.4 (208-180);
hind foot, 49.5 (51-47); the average weight of 29 adult specimens of
both sexes was 114.5 grams (131.9-98.0).
Averages for 17 adult females: Total length, 326.4 millimeters
(349-310); tail vertebræ, 188.8 (208-179); weight (16 individuals),
113.7 (131.9-98.0); excluding pregnant females, 13 individuals
averaged 112.9 grams (131.9-98.0).
Averages for 13 adult males: Total length, 326 millimeters (345-311);
tail vertebræ, 187.8 (202-168); weight, 116.8 grams (129-100).
There appears to be no significant difference in the measurements and

weights of males and females, with the possible exception of the
comparison of adult males and adult nonpregnant females.

OCCURRENCE.
GENERAL DISTRIBUTION.
Dipodomys spectabilis spectabilis is found in southeastern Arizona, in
northwestern, central, and southern New Mexico, in extreme western
Texas, in northern Sonora, and in northern and central Chihuahua (Fig.
1). A subspecies, D. s. cratodon Merriam, has been described from
Chicalote, Aguas Calientes, Mexico, the geographic range of which lies
in central Mexico in portions of the States of Zacatecas, San Luis
Potosi, and Aguas Calientes.
HABITAT.
In the Tucson region spectabilis is typically a resident of the Lower
Sonoran Zone. This is perhaps the principal zone inhabited over its
entire range, but the animal is often found in the Upper Sonoran also,
and in the Gallina Mountains of New Mexico Hollister found it
invading the yellow pine Transition where the soil was dry and sandy
and the pine woods of open character. The same observer found it
common in grassy and weed-grown parks among the large junipers,
pinyons, and scattering yellow pines of the Bear Spring Mountains, N.
Mex. Bailey calls attention to the fact that the animal apparently does