Arizona \ 
Exp. Sta. / 
LIFE HISTORY OF THE KANGAROO RAT. 
33 
abundant, as on the Range Reserve, may well be a factor in in- 
creasing soil porosity and fertility; for in the course of time they 
probably have succeeded in plowing and cultivating the whole sur- 
face layer of the soil. They may thus be a factor in ecologic suc- 
cession, tending to improve the character of the soil and adapt it 
to another stage. 
Doubtless their own workings afford the only shelter the animals 
know. In the course of our digging in one mound, the occupant, 
an adult male, did not forsake the den until the excavation was 
three-fourths completed; and even then it did not leave by a bur- 
row leading away from our operations, but came toward us, escaped 
the active efforts of four individuals bent on its capture, and ran 
speedily along a used runway toward another burrow several me- 
ters distant. A sack had been stuffed in the mouth of this, how- 
ever, and, baffled, the rat then returned to the original burrow and 
was captured. Observations on other rats thus driven from the home 
mound indicate that they are very familiar with the runways of 
the vicinity^ of the mound and the various subsidiary burrows, and 
it is a question whether they need to see clearly to follow these runs. 
Apparently they never attempt to escape by forsaking their well- 
traveled runways. Tests of the maze-running ability of these ani- 
mals by animal-behavior experts would be of extraordinary interest, 
in view of the character of the homes which they always inhabit 
and the network of runs on the outside. 
COMMENSALS AND ENEMIES. 
COMMENSALS. 
It is doubtful whether any animals live in a truly commensal re- 
lationship with spectdbilis, but of not unfriendly associates there 
are a great number. It is the experience of Bailey, corroborated 
by observations of Vorhies on living animals, that these kangaroo 
rats are active in defending their caches of food, and will even fight 
individuals of the same species savagely and to the death. One 
moonlight night a strange individual was liberated on a mound. 
It deliberately entered one of the openings, but after about two 
minutes' time made an exceedingly rapid exit, running rapidly out 
of sight as if pursued, though the owner of the home did not ap- 
pear outside of the burrow. There can be little doubt that the 
stranger was precipitately ejected by the owner. We suspect, though 
this is a point difficult to prove satisfactorily, that merriami does 
not always store food supplies for itself, but visits the burrows of 
spectabilis regularly to pilfer the seed stored therein. The observed 
facts thus far recorded which suggest this are that in no merriami 
burrow examined has a store of food been found, and also that in 
