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. T) 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 clog 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- 

 nisoni 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 



