ANIMAL BEHAVIOR — WALKER 273 



probably the least regular. 1 have observed that each of my pet pocket 

 mice {Perognathus), kangaroo rats {Dipodomys), and grasshopper 

 mice {Onychomys) had its own very definite time to wake up and to 

 go to bed. One little pocket mouse would come out of his nest about 

 4 o'clock in the afternoon during the winter. With the approach of 

 spring and the lengthening of the days he did not get up quite so 

 early ^ and during the longest days of summer he did not appear until 

 about 7 o'clock. Another individual of the same species, "Bitty," 

 regularly stayed in bed until about an hour or an hour and a half later 

 in the evening. In the morning I found that both were almost 

 invariably in bed by daylight. 



SELF-PRESERVATION 



"He who fights and runs away, may live to fight another day" gen- 

 erally holds true throughout the animal kingdom, for animals do not 

 ordinarily seek encounters with others unless it be to obtain food, 

 shelter, or mates. Combats to the death are rare. By the elimination 

 process that nature has followed so successfully, the individuals that 

 are strong and vigorous in searching for food, in capturing their prey, 

 in fighting for their homes or in gaining mates are enabled to per- 

 petuate their characteristics, while those that are weaklings in these 

 contests are not. 



The methods of avoiding detection or of being caught in dangerous 

 situations are, like the methods of escaping from enemies, even more 

 numerous than are the species of animals, for each species has many 

 problems of this kind to solve. 



Many human beings are definitely opposed to any new proposal, 

 particularly if they do not fully understand it. This is merely a 

 remnant of a trait that is essential to the preservation of an animal 

 species. For animals must be suspicious of anything they do not under- 

 stand, such as strangers, unaccustomed food, or new surroundings. 

 The stranger animal may be dangerous, the food may be poisonous, 

 or the surroundings may conceal a trap ; hence the animals that are 

 not suspicious and do not convince themselves of the safety of a new 

 thing before they try it may be eliminated. 



Since self-preservation is the first impulse of the individual and is 

 essential to the perpetuation of every species, all animals must have 

 some means of defense. All too frequently we think of animals in 

 the terms of whether or not they are dangerous or vicious. In general, 

 they are not dangerous except when they find it necessary to put up a 

 show of force to stop aggression. On this subject, it may be said that 

 when animals appear to us to be vicious, savage, or ill-tempered, this 

 is almost invariably their way of warning us to leave them alone, of 

 letting us know that they do not want trouble and that they are cour- 



