ANIMAL BEHAVIOR — WALKER 283 



DRINKIKG 



We usually think of water as being fully as important as food to 

 living creatures. Such, however, is not true in many instances. 

 Animals that live in desert regions have, through long periods of 

 evolution, developed ways of surviving with a minimum of moisture 

 obtained from their food. The most specialized of these are some 

 of the rodents such as the pocket mice and kangaroo rats of the 

 southwestern United States, the jerboas {Jaculus) of Asia and north- 

 ern Africa, and many others. These mammals live in regions 

 where the rainfall is very scant over much of their range and where 

 water is practically unobtainable. They have, theretofore, become 

 adapted to living with almost no water to drink. During the very 

 short time when there may be green vegetation they may eat some 

 of it. At other times they obtain no moisture except perhaps an 

 occasional drop of dew; but their needs are adequately supplied 

 by chemical processes that take place vv'ithin their own bodies, where 

 the constituents of dry seeds and other vegetable food are converted 

 into moisture by oxidation. 



Vernon Bailey, for many years Chief Field Naturalist of the 

 United States Biological Survey, has taken unusual interest in the 

 desert animals and has discussed in an admirable manner their 

 problem of obtaining moisture.^ He has found that many animals of 

 arid regions eat roots, tubers, and fleshy stems of plants such as 

 cacti and others that contain a high proportion of moisture even 

 during periods of drought, in this way probably obtaining all the 

 water they need without having to manufacture it by oxidation. 



I have often offered water to pocket mice, kangaroo rats, grass- 

 hopper mice, and other desert animals to make certain that they 

 did not suffer from lack of moisture. Almost invariably they refuse 

 it, though occasionally they may sip a little and then not touch 

 water again for months. 



One pocket mouse, however, a very old male, took to using water 

 rather regularly. He lived in captivity 8 years and was apparently 

 adult when captured. It may be that as he became older his normal 

 ability of converting dry food into moisture became impaired so 

 that he required moisture in order to survive. It is possible that the 

 unusual care that I gave liim enabled him to live to a greater age 

 than he could have reached in a wild state. Another animal of 

 the same kind seemed greatly offended when I offered her water. 

 On a few occasions I dropped a single small drop of water on her 

 and was much amused by her violent antics of rolling in the sand 

 to remove the offending substance from her coat. I am convinced 



* Bailey, Vernon, Sources of water supply for desert animals. Scl. Monthly, vol. 17, No. 1, 

 pp. 16-86, 1923. 



