2 BULLETIN 1227, U. S. DEPARTMENT OF AGRICULTURE 
mates of damage will be more accurate and convincing when based 
on controlled field tests. The difficulties include lack of information 
regarding the life histories of the animals concerned; necessity for 
evolving new methods of fencing, organization, and administration; 
expense of adequate fencing and inspection; and remoteness of the 
field of operations from headquarters. . 
The most important of the species of rodents which narrow the 
margin of profit of the farmer and stockman in the Western States 
are prairie dogs, ground squirrels, pocket gophers, and jack rabbits. 
Among these, none does greater damage to range grasses than the 
prairie dog, referred to more than 20 years ago as “ one of the most 
pernicious enemies to agriculture ” (Merriam, 1902, p. 263). Hollis- 
ter (1916, p. 7) writes: “ Prairie dogs are unquestionably responsible 
for great annual damage to crops and pasturage. In certain areas the 
destruction amounts to virtually the entire forage. Crops of grain 
and cultivated hay are often entirely ruined unless drastic pre- 
ventive measures are taken.” But “in other out-of-the-way places 
the animals do not interfere in the least with the operations of man.” 
Almost anyone who has had opportunity for observation will have 
been impressed with the destructive effect of the prairie dog on the 
forage grasses in the vicinity of its “ towns,” especially during dry 
years. Charles Springer, who, during the World War, was chairman 
of the executive committee of the New Mexico council of defense, 
writes (letter of January 6, 1919): 
Regarding the extent of damage done to the range by prairie dogs, opinions 
differ, and, of course, it depends upon the degree of infestation. In the 50,000- 
acre unit now being investigated and treated in the Moreno Valley, in Colfax 
County, the prairie dogs destroyed nearly all the grama grass, and I believe the 
damage to that range amounted to 75 per cent. Generally the damage done 
by prairie dogs in the infested areas with which I am familiar ranges from 
40 or 50 per cent to 100 per cent. I have seen in Rio Arriba and Sandoval 
Counties, and in some of the other counties, large areas rendered practically 
worthless for grazing purposes by these pests. It is safe to estimate that the 
annual damage to ranges in New Mexico has amounted to destroying the grass 
on more than 6,000,000 acres of the very choice grazing land of the State, the 
areas selected and infested by prairie dogs being generally the best grama- 
grass flats and draws. 
In order to determine quantitatively the damage done by prairie 
dogs to forage grasses under different conditions, three sets of ex- 
perimental areas were established during the year 1918 in northern 
Arizona (at Coconino, near Grand Canyon; at Williams; and at 
Seligman) by the Bureau of Biological Survey, the Carnegie Institu- 
tion of Washington, and the Forest Service. Some of the results thus 
far obtained are discussed here. 
The prairie dog found in northern Arizona and concerned in the 
experiments here reported is the Zuni prairie dog (Cynomys gun- 
nisont zuniensis Hollister). This subspecies is of wide distribution 
being found in central, northern, and eastern Arizona, in central 
and northwestern New Mexico, and in southwestern Colorado. Its 
destruction of forage grasses may be regarded as fairly typical of the 
activities of prairie dogs in general. 
The procedure in the conduct of the experiments was either to 
fence in the prairie dogs on a particular infested tract, or (as at 
Seligman) to permit free entry of prairie dogs while excluding 
cattle; to inclose also a contiguous area of similar size, so that it 
