1-4 BULLETIN 1091, U. S. DEPARTMENT OE AGRICULTURE. {bSlnS, 
nacity toward each other. While three or four individuals may 
sometimes be trapped at a single mound, more than two are seldom 
so caught, and most often only one in one night. Trapping on suc- 
cessive nights at one mound often yields the larger number, yet in 
some cases the number is explained by the fact that two or three 
nearly mature young are taken, and the capture of several individ- 
uals at a single mound can not be taken to indicate that all are from 
the one den. Our investigations tend strongly to the conclusion that 
only one adult occupies a mound, except during the period when the 
young are in the parental (or maternal) den. In the gassing and 
excavating of 3'5 or more mounds we have never found more than one 
animal in a den. except in one instance, and then the two present 
were obviously young animals. 
SENSE DEVELOPMENTS. 
Without making special investigations through a study of behavior 
or other special methods, one can speak in only general terms re- 
garding what appear to be the special sense developments of kangaroo 
rats. The eyes are large, as is very often the case in nocturnal ani- 
mals, and when brought out into the bright light of day the rats 
perhaps do not see well. Yet. if an animal leaves a den which is in 
process of excavation, and follows one runway, even in bright sun- 
light, it makes excellent speed to the next opening, often a distance of 
several yards. Whether this is accomplished chiefly by the aid of 
sight or in large measure by a maze- following ability, such as ex- 
periments have shown some rodents to have, can not be stated without 
precise experimentation. Marked ability to follow a maze would 
not be at all surprising in view of the labyrinthine character of the 
underground passages which make up the normal habitation. 
When watching beside a mound by moonlight one is impressed with 
the fact that the rats possess either a very keen sense of hearing or 
of sight, probably both. The very slightest movement or noise on 
the part of the observer results, with a timid individual, in an in- 
stantaneous leax^ for safety, a disappearance into the burrow so 
sudden as to be almost startling. All attempts to obtain flashlight 
photographs at the mounds were failures, the animal either having 
gotten completely out of the field before the light flashed following 
the pull of the trigger, or leaving merely an indistinguishable blur 
on the plate as it went, and this in spite of carefully hiding the trigger 
chain behind a screen. A slight noise accompanying the trigger 
action gave the alarm in one case, and in another the length of time 
of the flash was sufficient for the get-away. The marvelous quick- 
ness of the animal clearly indicates a remarkably short reaction time. 
