Without making special investigations through a study of behavior or
other special methods, one can speak in only general terms regarding
what appear to be the special sense developments of kangaroo rats. The
eyes are large, as is very often the case in nocturnal animals, 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 sunlight, 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 experiments 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 instantaneous leap 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 quickness of the animal clearly indicates a
remarkably short reaction time. Occasionally a bold individual is
found, as in the case of one which came out repeatedly, even after being
flashed twice in the same night.
Certain peculiar physical characteristics suggest a relationship to
sense reactions. On these, however, the authors are not prepared to do
more than offer suggestions for future work. The extremely large
mastoids found in kangaroo rats suggest a connection in some way with
special developments of the sense of hearing or of balance. It may be
noted that an intermediate condition between the kangaroo rats and the
majority of rodents in respect to this character is to be found in the
pocket mice (_Perognathus_), which belong to the same family. Herein
lies a field for some interesting experimentation and discovery.
The small, pointed nose might suggest a not overkeen sense of smell, and
there appears no reason to believe that this sense is particularly well
developed. However, the turbinals are very complex. The vibrissæ are
long and sensitive, and may indicate a special development of the sense
of touch as an adaptation to nocturnal habits and to life in an
underground labyrinth. The long, well-haired tail doubtless serves as an
important tactile organ as well as a balance.