ANIMAL BEHAVIOR—ERNEST P. WALKER 269 
CLEANLINESS 
Almost all animals are fastidiously cleanly about their persons and 
their homes. Because of the fact that many animals live on or in 
the ground or on trees or other surfaces that frequently are dirty 
according to our standards, we often erroneously consider the animals 
to be uncleanly. As a matter of fact, practically every animal takes 
great pains to avoid soiling its coat, and when it does unavoidably 
become soiled, the animal at the first opportunity painstakingly cleans 
itself by shaking, rolling in the sand, washing in water, or licking itself. 
Even those pests, the common Norway rat, roof rat, and house mouse, 
which have found that they can obtain food and shelter in man’s 
filthy surroundings, endeavor to keep themselves clean. If they are 
observed when not alarmed, it will be seen that they carefully pick 
their way through their surroundings in an effort to avoid soiling 
themselves, and after they have finished their exploration they will 
invariably be seen to groom carefully. If one will part the fur of 
small mammals it will be seen that the skin is generally immaculately 
clean. 
A star-nosed mole (Condylura cristata) that I am keeping as a pet 
comes out of the ground, goes into a dish of water and at once begins 
grooming. In a few minutes it has washed thoroughly. 
Animals have developed many ways for keeping themselves and 
their nests clean. Apparently flying squirrels rarely void excreta 
during their entire sleeping period, which may be as much as 16 hours. 
Obviously they wish to keep the inside of the tree or other nest loca- 
tion clean, so wait until they go out at night when they can see 
clearly and there is a minimum of danger from outside enemies. 
Many of the burrowing mammals have little toilet rooms that open 
off of the main burrow where they deposit their excrement, thus keep- 
ing the main burrow clean. Young North American opossums 
(Didelphis virginiana) of an age to be in the pouch or still be clinging 
to their mother apparently do not release their excretion unless they 
are stroked on the lower abdominal region. This is probably a pro- 
vision for keeping the pouch clean until such time as the mother is 
ready to clean the little ones. 
POSTURES 
The new-born babies of many of the small mammals naturally lie on 
their backs. This leaves them in the proper position for nursing 
when the mother hovers over them, protecting them, hiding them, 
and keeping them warm. 
Most hoofed animals do not voluntarily sit on their haunches. A 
horse assumes this position briefly when getting up, but this does not 
constitute true sitting. The exceptions to the rule are the tapirs, 
