Life History of the Kangaroo Rat | Page 3

lies principally to the west of that of spectabilis,
and the two do not, so far as known, overlap. On the other hand,
merriami and ordii, and subspecies, occur over a large part of the range
of spectabilis, living in very close proximity to its burrows; merriami is
even suspected of pillaging the stores of spectabilis. The range of
merriami, however, is much more extensive than that of spectabilis
(Fig. 1), which argues against a definite ecological dependence or
relationship. Separation of the four forms mentioned may be easily
accomplished by the following key:
Key to Species of Dipodomys in Arizona.
a^1. Size much larger (hind foot and greatest length of skull more than
42 millimeters); tail tipped with white.
b^1. Upper parts dark brownish buffy; tail dark brownish or blackish
with more sharply contrasted white tip; interparietal broader, distinctly
separating mastoids (range in Arizona mainly southeastern part)
=Dipodomys spectabilis.=
b^2. Upper parts light ochraceous-buffy; tail pale brownish with less
sharply contrasted white tip; interparietal narrower, reduced to mere
spicule between mastoids (range in Arizona mainly southwestern part)
=Dipodomys deserti.=
a^2. Size much smaller (hind foot and greatest length of skull less than
42 millimeters); tail not tipped with white.

b^1. Hind foot with four toes =Dipodomys merriami.=
b^2. Hind foot with five toes =Dipodomys ordii.=
On account of the small size, merriami and ordii do not require detailed
color comparison with the other two. The general color of the
upperparts of spectabilis is much darker than that of deserti; whereas
spectabilis is ochraceous-buff or light ochraceous-buff grizzled with
blackish, deserti is near pale ochraceous-buff and lacks the blackish.
The color of the upperparts alone amply suffices to distinguish
spectabilis and deserti; but the different coloration of the tail is the
most obvious diagnostic feature. The near black of the middle portion
of the tail, the conspicuous white side stripes, and the pure white tip
make the tail of spectabilis stand in rather vivid contrast to the
pale-brown and whitish tail of deserti.
The dens of the two larger species of Dipodomys--spectabilis and
deserti--can be distinguished at a glance from those of the two
smaller--merriami and ordii--by the fact that the mounds of the former
are usually of considerable size and the burrow mouths are of greater
diameter. On the Range Reserve merriami erects no mounds, but
excavates its burrows in the open or at the base of Prosopis, Lycium, or
other brush. The mounds of spectabilis are higher than those of deserti,
the entrances are larger, and they are located in harder soil (Pl. III, Fig.
1). The dens of deserti are usually more extensive in surface area than
those of spectabilis, and have a greater number of openings (Pl. III, Fig.
2).
[Illustration: PLATE II. FIG. 1.--WINTER VIEW OF AREA
INHABITED BY KANGAROO RATS.
A water-hole scene on the U. S. Range Reserve at the base of the Santa
Rita Mountains, Ariz., where cooperative investigations are being
conducted to ascertain the relation of rodents to forage. This is typical
of a large section of country occupied by _Dipodomys spectabilis
spectabilis and Dipodomys merriami_. The brush is mesquite
(Prosopis), cat's-claw (Acacia), and paloverde (Cercidium).]

[Illustration: PLATE II. FIG. 2.--KANGAROO RAT COUNTRY
FOLLOWING SUMMER DROUGHT.
An area of the U. S. Range Reserve in the autumn of 1918, showing the
result of failure of summer rains. Such a condition is critical not only
for the stockmen but also for kangaroo rats and other desert rodents,
and results in competition between them as to which shall benefit by
what the range has to offer.]
[Illustration: PLATE III. FIG. 1.--KANGAROO RAT MOUND
(DIPODOMYS S. SPECTABILIS).
Typical Dipodomys s. spectabilis mound on the Range Reserve, under
shelter of desert hackberry (Celtis pallida). Most dens on the reserve
are located in the shelter of brush plants, the more important being
mesquite (Prosopis velutina), cat's-claw (Acacia spp.), and the desert
hackberry. (See also Pl. VIII Fig. 2.)]
[Illustration: PLATE III. FIG. 2.--KANGAROO RAT MOUND
(DIPODOMYS DESERTI).
Den of Dipodomys deserti deserti, showing typical wide, low mound
with numerous entrance holes. This species excavates its den in soft,
sandy soil. The tree is a species of Dalea.]

DESCRIPTION.
GENERAL CHARACTERS.
Size large; ears moderate, ear from crown (taken in dry skin) 9 or 10
millimeters; eyes prominent; whiskers long and sensitive; fore feet
short and weak; hind feet long and powerful, provided with four
well-developed toes; tail very long, usually 30 to 40 per cent longer
than the body. Cranium triangular, the occiput forming the base and the
point of the nose the apex of the triangle, much flattened, auditory and
particularly mastoid bullae conspicuously inflated.

COLOR.
General color above, brownish buffy, varying in some specimens to
lighter buffy tints, grizzled with black; oblique hip stripes white; tail
with dark-brown or blackish stripes above and below, running into