8 



NOETH AMEEICAN FAUNA. 



[ NO. 39. 



farmers each year, and it is necessary in farming areas to use every 

 possible means of restraining their increase and checking their depre- 

 dations. In ^vild land, on the other hand, their presence is highly 

 beneficial, not only because they stir the soil and enrich it by burymg 

 vegetation under their mounds, but also because they form a net- 

 work of underground channels which aid materially in retaining 

 water and carrying it deeper into the ground. Such of their beneficial 

 habits as have operated for ages in enriching the western soils are 

 far overbalanced in agricultural lands by their destructive habits. 

 On lands newly brought under cultivation it is often necessary to 

 wage an active campaign against gophers, in order to render the 

 crops fairly safe. (See footnote, p. 14.) 



The present paper describes the recognizable species and sub- 

 species and defines their geographic distribution so far as at present 

 known. 



GENERAL HABITS. 



BURROWS. 



Pocket gophers of the genus Thomomys are burrowing animals 

 which spend most of their lives underground. The several species 

 have practically the same habits except as modified by environment. 

 They are sturdy little miners, drifting their tunnels on and on in 

 search of food, throwing out little heaps of earth along the lines of 

 excavation, and then quickly closing the doorway. The tunnels vary 

 from about 6 inches to a foot below the surface, and from about 1^ 

 to 3 inches in diameter, according to the size of the gopher. The 

 length of the tunnels is practically interminable and their course 

 varies from a winding network to long direct lines. 



The character of the burrows is determined by the food supply. 

 A row of potatoes may be followed across a field, or the spreading 

 roots of an apple tree may hold the attention of the gopher for some 

 time. If food is scarce the rows of mounds reach in direct lines for 

 long distances, but when it is abundant they wind back and forth 

 withm a limited area. While the males move about more freely at 

 the beginning of the breeding season and there are indications of rare 

 migrations, pocket gophers are evidently the most restricted in their 

 habitat of any of our native mammals. Even moles, which live more 

 completely underground, burrow more rapidly and travel more 

 widely. The whole summer's line of hills of one gopher can often 

 be seen at a glance. The animals rarely leave an alfalfa or potato 

 field, but hurry across waste places. Under ordinary circumstances, 

 however, a gopher often spends a year on a single acre, and perhaps 

 the next year on an adjoining one. Most gophers probably never 

 get 40 rods from where they were born, but where environment is less 

 favorable and the gopher is more active, he may extend his tunnels 

 for haK a mile or possibly a mile during his career. 



