114 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 7’. botte (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 zodlogists, 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 
