THE BURROWING RODENTS OF CALIFORNIA AS 

 AGENTS IN SOIL FORMATION 1 



By Joseph Grinnell 



[With 3 plates] 



The interrelations between vertebrate animals and their environ- 

 ments are exceedingly variable and far-reaching. To base any con- 

 clusion upon a contrary assumption has proven dangerous, for in 

 specific cases such procedure has led people to expend effort and sub- 

 stance not only needlessly but definitely against their own best inter- 

 ests. An inference as to the relationships between some certain wild 

 mammal and human affairs may at first thought look to be perfectly 

 obvious and unquestionable. Extended examination, however, may 

 show that many factors previously overlooked are concerned, and 

 the comprehension of these may lead to an entirely different view. 



The species and subspecies of mammals occurring in California, so 

 far as known at the present moment, number 410 ; 227 of these belong 

 to the order Rodentia. Of these, 109 are essentially burrowing ro- 

 dents; that is, they have their breeding quarters, at least, beneath 

 the surface of the ground, this circumstance entailing more or less 

 digging, and some of them spend practically all of their time within 

 their subterranean tunnels. These rodents of essentially burrowing 

 habit include the following groups: The ground squirrels, with 18 

 species ; the kangaroo mice, with 2 species ; the pocket mice, with 23 

 species; the kangaroo rats, with 33 species; and the pocket gophers, 

 with 33 species. 



To express the above facts in more general terms: Of the total 

 number of species of mammals living within the confines of the 

 State, more than one-half are rodents, and of the rodents alone, just 

 one-half are of the burrowing category ; rodents that burrow consti- 

 tute, by species, one-fourth of all the mammals in California. It 

 may further be observed that rodents which burrow are more or less 

 plentiful throughout the West. And here is another surprising fact, 

 namely, that only one of the seven genera of mammals to which our 

 burro wers belong is represented in the United States east of the 



1 Contribution from the Museum of Vertebrate Zoology of the University of California. 

 Read at meeting of California Chapter of Sigma Xi, Oct. 12. 1921. Reprinted by permis- 

 sion from Journal of Mammalogy, vol. 4, No. 3, August, 1923. 



339 



