12 BULLETIN 1227, U. S. DEPARTMENT OF AGRICULTURE . 



many modifying conditions in different localities which may operate 

 to increase or diminish the amount of damage. Accurate generaliza- 

 tion covering an entire forage type can only be based on quantitative 

 experiments carried over a period of years in several representative 

 localities. But at the rate of damage indicated by the measured 

 results here given, the grazing capacity of the range would almost 

 inevitably be reduced even in a favorable year, and in a drought 

 year the effect of rodent grazing would be critical. 



Prairie dogs tend to congregate into " towns " or communities, 

 which are occupied continuously until the vegetation is used up. 

 The range in and around the town is severely grazed at all times, and 

 sometimes, particularly in dry years, the grasses are grazed not only 

 to the ground, but all the buds and even the tops of the roots are 

 eaten, the grasses being thereby utterly destroyed. When the dam- 

 age reaches this point it is spectacular and impressive. 



In many localities through the Western States there exist great 

 areas of choice range land on which the vegetation has been com- 

 pletely destroyed by these rodents, and usually the margin of the 

 affected area shows a series of prairie-dog towns gradually en- 

 croaching toward the untouched grassland. The animals do not 

 readily abandon their burrows, not in fact until the distance to the 

 grazing area becomes too great for safety. In consequence the heavily 

 overgrazed tracts are gone over again and again, so that by the time 

 they are deserted there is often not one small shoot left to form the 

 nucleus from which the range can be reseeded. 



The denuded areas are sometimes wholly bare in dry season, but 

 are usually occupied by stands of weeds altogether unfit for grazing 

 either by stock or by prairie dogs. With the slow movement of 

 plant succession in desert or semiarid regions, particularly under 

 present range-control conditions, recovery from prairie-dog grazing 

 must necessarily be slow. Complete eradication of the entire rodent 

 population and proper grazing management does, however, give the 

 grasses a chance to move back into the denuded area, and gradually 

 to restore the range. It is obvious that quantitative determination 

 of present damage to the range must be based on experiments con- 

 ducted in the grassland border of an occupied prairie-dog town or in 

 some colony where the grass has not been entirely destroyed. 



It is not improbable that, under original conditions prevailing 

 within the geographic range of the prairie dog, a practical equilib- 

 rium between the grass and the rodents had been established, so 

 that the prairie dogs and the grasses rather constantly maintained 

 their ranges, subject, of course, to fluctuations in climate and certain 

 other possibly modifying factors. The coming on the scene of man, 

 with his herds of grazing domestic animals, has completely upset 

 this original balance and has turned the tide toward destruction of 

 the forage plants. The killing of coyotes and other predatory ani- 

 mals, fully justified on certain areas where they do more damage to 

 species of wild game and to livestock than they do good in destroying 

 rodents, has removed one of the normal checks upon the prairie 

 dogs and has tended still further to upset the balance. As an offset 

 for these two modes of interference with the natural equilibrium, the 

 Biological Survey and various cooperating agencies have undertaken 

 systematic campaigns for the extirpation of the rodents. If utter 



