2 BULLETIN 1091, U. S. DEPARTMENT OF AGRICULTURE, {^l'no?! 
been found that such rodents as prairie dogs, pocket gophers, mar- 
mots, ground squirrels, and rabbits take appreciable and serious toll 
of the forage on the open grazing range; in fact, that they reduce 
the carrying capacity of the range to such an extent that expenditures 
for control measures are amply justified. Current estimates place 
the loss of goods due to rats and mice in warehouses and stores 
throughout the United States at no less than $200,000,000 annually, 
and damage to the carrying capacity of the open range and to culti- 
yated crops generally by natiye rodents in the AVestern States at 
$300,000,000 additional; added together, we haye an impressiye total 
from depredations of rodents. 
The distribution and life habits of rodents and the general con- 
sideration of their relation to agriculture, forestry, and grazing, with 
special reference to the carrying capacity of stock ranges, is a subject 
that has receiyed attention for many years from the Biological Sur- 
yey of the United States Department of Agriculture. As a result 
of the inyestigations conducted much has been learned concerning 
the economic status of most of the more important groups, and the 
knowledge already gained forms the basis of the extensive rodent- 
control work already in progress, and in which many States are co- 
operating with the bureau. If the work is to be prosecuted intelli- 
gently and the fullest measure of success achieved, it is essential that 
the consideration largely of groups as a whole be supplemented by 
more exhaustiye treatment of the life histories of individual species 
and of their place in the biological complex. The present report is 
based upon inyestigations. chiefly in Arizona, of the life history, 
habits, and economic status of the banner-tailed kangaroo rat. Dipo- 
domys spectabilis spectabilis Merriam (PI. I). 
INVESTIGATIONAL METHODS. 
Some 18 years ago (in 1903) a tract of land 49.2 square miles in 
area on the Coronado National Forest near the Santa Eita Mountains. 
Pima County, southern Arizona, was closed to grazing by arrange- 
ment between the Forest Service and the Agricultural Experiment 
Station of the Uniyersity of Arizona.- Since that time another small 
tract of nearly a section has been inclosed (Griffiths, 1910. 7 1 ) . This 
total area of approximately 50 square miles is known as the United 
States Eange Reserve, and is being devoted to a study of grazing con- 
ditions in this section and to working out the best methods of adminis- 
tering the range (PI. II. Fig. 1). 
1 References in parentheses are to the Bibliography, p. 40 (the last figure being t<> the 
page of the publication). References to auUiorities where no citation of literature is 
appended relate for the most part to manuscript notes in the files of the Biological Survey 
or the University of Arizona Agricultural Experiment Station. 
