316 GRAZING INDICATORS. 



Rodent eradication. — Smith (1899: 15) was apparently the first to emphasize 

 the damage done by rodents to the range and to urge the systematic extermi- 

 nation of prairie-dogs and jack-rabbits. While much has been said and 

 written on the control and extermination of prairie-dogs in particular since 

 1900, effective campaigns against these and other rodents are recent develop- 

 ments. During the last five years especially, the Biological Survey has 

 carried on systematic and effective work in the eradication of both prairie- 

 dogs and ground-squirrels, in cooperation with various States, as well as with 

 the Forest Service and with private individuals (Bell, 1917; Lantz, 1918). 

 In addition, California has organized an extensive campaign through its 

 Rodent Control Section. It has also come to be recognized that jack-rabbits 

 are often exceedingly destructive to the range, and the work of Vorhies (1919) 

 has shown that the kangaroo-rats of the Southwest must also be included 

 among the major pests. While various methods have been used to extermi- 

 nate or control rodents, that of poisoning has become the standard, because of 

 its economy and efficiency. However, it has become clear that complete 

 eradication is possible only through poisoning for two or three successive 

 seasons, and that re-immigration can be controlled only by dealing with large 

 and more or less natural areas and by the extermination of invading colonies 

 from time to time. 



The absence of accurate knowledge as to the amount and kind of damage 

 done to the range by rodents, and especially of the rate and degree of recovery 

 in various types after eradication, led the writer to suggest the desirability of 

 cooperative studies to the Biological Survey, the Forest Service, and the Uni- 

 versity of Arizona. As a consequence, fenced areas for such investigations 

 were established in 1918 in the Bouteloua-Aristida grassland of the Santa Rita 

 range reserve and in the Bouteloua gracilis climax of northern Arizona near 

 Seligmann and Williams. The latter were designed to study the recovery 

 after the eradication of prairie-dogs, while the former were to permit a more 

 intensive study with reference to jack-rabbits, and especially kangaroo-rats, 

 which had just been shown by Vorhies to cause even more serious damage. 

 A series of three exclosures was installed in the Bouteloua rothrockii-Aristida 

 calif ornica type of the reserve (plate 82). The first was fenced against both 

 rodents and cattle, and the second and third against cattle alone, but differing 

 in that the rodents were killed out of one. A second exclosure was established 

 in the Bouteloua eriopoda-Aristida divaricata type, which was also fenced 

 against rodents and cattle. For the sake of a direct determination of the 

 amount of forage consumed by jack-rabbits and kangaroo-rats, two inclosures 

 were located in one of the best areas of Bouteloua roihrockii. In one of these 

 were placed two rabbits, in the other two kangaroo-rats. Permanent quad- 

 rats were located for measuring the effects in the various inclosures as well as 

 in the pastures by means of charting and clipping. The critically dry sum- 

 mer of 1918 almost completely prevented the growth of grass and summer 

 annuals, and practically all quadrats contained less growth in the fall than in 

 the spring. The winter rains were nearly normal and so well distributed that 

 the growth of winter annuals was exceptional. As a consequence, the various 

 fenced areas showed striking improvement in total production over the 

 pastures. This was not only true of the cattle-proof exclosures, but of the 

 rodent ones likewise, proving that the rodents also take heavy toll from the 

 winter annuals as well (plate 82, b). 



