on the Range Reserve, the rodents are widely distributed
over a considerable area. Occasionally, as in the vicinity of Rio
Alamosa, N. Mex., as reported by Goldman, they occur only in small
colonies.
[Illustration: PLATE IV. FIG. 1.--RANGE CONDITIONS
FAVORING KANGAROO RATS.
View on higher portion of Range Reserve, showing type of country
where Dipodomys s. spectabilis is most abundant. Good growth of
grama and needle grasses in October, following summer growth and
before grazing off by cattle and rodents.]
[Illustration: PLATE IV. FIG. 2.--RANGE CONDITIONS LESS
FAVORABLE TO KANGAROO RATS.
View on lower portion of Range Reserve, where Dipodomys s.
spectabilis is less abundant. Vegetation consists principally of Lycium,
mesquite, rabbit brush, and cactus, there being very little grass.]
HABITS.
EVIDENCE OF PRESENCE.
MOUNDS.
One traveling over territory thickly occupied by the banner-tailed
kangaroo rat is certain to note the numerous and conspicuous mounds
so characteristic of the species, particularly if the region is of the
savannah type, grassy rather than brushy. These low, rounded mounds
occupy an area of several feet in diameter, and rise to varying heights
above the general surface of the surrounding soil, the height depending
rather more upon the character of the soil and the location of the mound
as to exposure or protection than upon the area occupied by the burrow
system which lies within and is the reason for the mound.
A den in sandy soil in the open may be of maximum size in area
occupied and yet scarcely present the appearance of a mound in any
sense, due probably both to the fact that the sandy soil will not heap up
to such a height over a honeycomb of tunnels as will a firmer or rocky
soil, and also to its greater exposure to the leveling action of rains and
the trampling of animals. These mounds are in themselves large enough
to attract some attention, but their conspicuousness is enhanced by the
fact that they are more or less completely denuded of vegetation and
are the centers of cleared areas often as much as 30 feet in diameter (Pl.
V, Fig. 1); and further that from 3 to 12 large dark openings loom up in
every mound. The larger openings are of such size as to suggest the
presence of a much larger animal than actually inhabits the mound.
Add to the above the fact that the traveler by day never sees the mound
builder, and we have the chief reasons why curiosity is so often aroused
by these habitations.
On the Range Reserve the mounds are usually rendered conspicuous by
the absence of small vegetation, but Nelson writes that in the vicinity of
Gallego, Chihuahua, they can be readily distinguished at a distance
because of a growth of weeds and small bushes over their summits,
which overtop the grass. In the vicinity of Albuquerque, N. Mex.,
Bailey reports (and this was recently confirmed by Vorhies) that the
mounds about the holes of spectabilis are often hardly noticeable.
Hollister writes that in the yellow-pine forests of the Gallina Mountains
the burrows are usually under the trunk of some fallen pine, both sides
of it in some cases being taken up with holes, there being some eight or
ten entrances along each side, the burrows extending into the ground
beneath the log. In the vicinity of Blanco, N. Mex., Birdseye says that
occasionally spectabilis makes typical dens but more often lives in old
prairie-dog holes (Cynomys), or in holes which look more like those of
D. ordii.
RUNWAYS AND TRACKS.
Still other features add to the interest in the dwelling places of
spectabilis. Radiating in various directions from some of the openings
of the mounds well-used runways are to be seen, some of them fading
out in the surrounding vegetation, but others extending 30, 40, or even
50 or more yards to neighboring burrows or mounds (Pl. V, Fig. 2; Pl.
VI, Fig. 1). These runways and the entrances to the mounds are well
worn, showing that the inhabitants are at home and are at some time of
day very active. The worn paths become most conspicuous in the
autumnal harvest season, when they stand out in strong contrast to
surrounding grass. One usually finds not far distant from the main
habitation one or more smaller burrows, each with from one to three
typical openings, connected by the trail or runway system with the
central den, and these we have called "subsidiary burrows" (Pl. VI, Fig.
2). These will be again referred to in discussing the detailed plan of the
entire shelter system.
Examination of the runways and of the denuded area about a mound
discloses an abundance of almost indecipherable tracks. The dust or
sand is ordinarily much too dry and shifting to record clear footprints,
and there are no opportunities to
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