434 



REPORT OP STATE GEOLOGIST. 



the larger animals having a vegetarian diet and has been an impor- 

 tant factor in their rapid extermination. For instance, a bison 

 could always find an abundance of grass unless in case of events 

 entirely beyond its control, such as extensive fires or prolonged and 

 deep snows. The strength of the individual, together with the 

 strength of the herd of which it was always a part, rendered each 

 animal practically secure from attacks of all enemies. While there 

 was some fighting for mates among the old males, the habit of asso- 

 ciating in herds of great size made this struggle of secondary im- 

 portance and the only way in which individuals were compelled 

 to adapt themselves to the environment was by migrating to new 

 feeding grounds as pastures were exhausted. 



On the other hand, a carnivorous animal is always compelled 

 to seek prey that is often nearly its equal in strength and speed. 

 Here cunning is at a premium, and mental capacity may determine 

 which individuals shall live and which shall perish. 



The construction of a den or nest is also, to a large degree, an 

 adaptation to the biological environment. The larger species of 

 grass-eaters trust to speed and strength to escape enemies; their 

 young are born in such a highly developed condition that they are 

 able to walk and run about almost immediately, and no nest or den 

 is ever constructed. 



But the young of most other mammals are born in a naked and 

 helpless condition. For their protection most animals construct 

 some kind of a nest, sometimes first making a den or burrow in 

 which to place it. This may be in part, for protection from the 

 physical elements, but is more largely for protection from enemies. 

 Nest-l)uilding is almost universal among the smaller rodents that 

 are sul)j(^cted to attacks from many enemies. However, bats that 

 are equally helpleSvS, spend most of the time on the wing or sus- 

 pended from the roofs of caves or the sides of hollow trees where 

 they are comparatively free from danger. Consequently they never 

 construct any sort of nest or home, but carry their helpless young 

 about from place to i)lace or leave them clinging to the most con- 

 venient resting place. 



The effects of home constructing upon an animal are of far- 

 reaching c()nse(ju(;nce. The instinct and intelligcnice of the animal 

 ar(; })r()ught into ])]i\y in selecting the site and material, and the sense 

 of ownership is devel(){)ed and combative ability maintained in the 

 defense of its home. The ownership of a home limits the range of 

 an animal and gives it a base from which to extend its activities, 

 just as llic j)oss('ssion of a liome gives a, man stability and responsi- 



