l4^p!^s"a.} LIFE HISTORY OF THE KANGAROO RAT. 33 



abundant, as on the Eange Reserve, may well be a factor in in- 

 creasing soil porositj" 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 runwaj^ 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 subsidiarj^ 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 spectabilis^ 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 vierHajini does 

 not always store food supplies for itself, but visits the burrows of 

 spectahilis regularly to pilfer the seed stored therein. The observed 

 facts thus far recorded which suggest this are that in no inernami 

 burrow examined has a store of food been found, and also that in 



