ch rodents as prairie dogs, pocket gophers, marmots, 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 cultivated crops generally by native rodents in the
Western States at $300,000,000 additional; added together, we have an
impressive total from depredations of rodents.

The distribution and life habits of rodents and the general
consideration of their relation to agriculture, forestry, and grazing,
with special reference to the carrying capacity of stock ranges, is a
subject that has received attention for many years from the Biological
Survey of the United States Department of Agriculture. As a result of
the investigations 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 cooperating with the
bureau. If the work is to be prosecuted intelligently and the fullest
measure of success achieved, it is essential that the consideration
largely of groups as a whole be supplemented by more exhaustive
treatment of the life histories of individual species and of their place
in the biological complex. The present report is based upon
investigations, chiefly in Arizona, of the life history, habits, and
economic status of the banner-tailed kangaroo rat, _Dipodomys
spectabilis spectabilis_ Merriam (Pl. 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 Rita Mountains, Pima County,
southern Arizona, was closed to grazing by arrangement between the
Forest Service and the Agricultural Experiment Station of the University
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 Range Reserve, and is
being devoted to a study of grazing conditions in this section and to
working out the best methods of administering the ran