11.4 ANIMAL COMPETITORS 



dian plains. "West of the Rockies occur a large 

 number of species, some very difficult to dis- 

 tinguish from one another, of which the reddish 

 Thomomys douglasi of the Columbia River 

 valley, and T. bottcc (chestnut above, reddish 

 brown below) of central and southern Cali- 

 fornia, are most notable. In many regions 

 they have increased rather than diminished 

 with civilization, owing to the destruction of 

 their natural enemies, to the loosening of the 

 soil by plowing and to the vast increase of food 

 afforded them by orchards, gardens and crops. 

 Though several genera and species are sepa- 

 rated by zoologists, from the farmer's point of 

 view there is a substantial likeness, not only in 

 their yellowish-gray or brownish, unmarked 

 coats ; their big, thick heads ; their short strong 

 legs ; their almost invisible ears and eyes ; the 

 massive incisors and capacious furry cheek- 

 pouches, opening outside the mouth; but in 

 the constant and fearful damage they work in 

 the field, orchard and nursery. 



Burrowing powers. The pocket-gopher digs 

 as long as he lives, and generally all winter, for 

 he does not hibernate, even at the coldest. All 



