Exp^'ste } LIFE HISTORY OF THE KANGAROO RAT. 11 



are at some time of day very active. The worn patlis 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" (PI. 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 see footprints of this 

 species recorded in good impressionable soil. Ver\^ characteristic 

 traces of kangaroo rats may be readily observed in the dust about the 

 mounds, however, and these are long, narrow, sometimes curving, 

 furrows made by the long tails as the animals whisk about their work 



or play, 



Signals. 



If a scratching or tapping sound be made at the mouth of a bur- 

 row, even in the daytime, one is likely to hear a muffled tapping in 

 response, and this may at times be heard while one is engaged in 

 excavating a mound. It has a chirring or fluttering quality, de- 

 scribed by Fisher as resembling the noise of a quail flying. Bailey 

 (1905, 148) is of the opinion that it is used as a signal of alarm, call 

 note, or challenge, a view which the present authors believe to be cor- 

 rect. During the winter of 1920-21, however, both Bailey and 

 Vorhies discovered that this sound, or a very similar one, is made 

 by the rapid action of the forefeet in digging. On one occasion 

 in the laboratory the sound was given by one of a pair and was 

 responded to at once by the other, the two being in separate but con- 

 tiguous cages. This observation, however, could not be repeated. 

 (Vorhies MS.) 



One evening, while working in the vicinity of the Burro Moun- 

 tains, N. Mex., Goldman heard a kangaroo rat near camp making 

 this thumping noise. Taking a lantern, he approached the den, very 

 cautiously, until within 10 feet. The kangaroo rat was just outside 

 the entrance of one of its burrows, and though moving about more or 

 less restlessly at first showed little fear, and kept up the thumping 

 or drumming at intervals. When making the noise the animal was 

 standing with the forefeet on the ground and the tail lying extended. 

 The noise seemed to be made with the hind feet only, and the vibra- 

 tion of the feet could be seen. The tapping was kept up for a second 

 or two at a time, the sounds coming close together and being repeated 



