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 
