Exp. Sta. \ 
Arizona / 
LIFE HISTORY OF THE KANGAROO EAT. 
19 
on stored materials. Xot infrequently a season of severe drought pre- 
cludes the possibility of any storage. The summer and fall of 1918 
was such a season on the Range Reserve (PI. II, Fig. 2). If food 
stores are inadequate at such a time the kangaroo rats must perish 
in considerable numbers. Fisher found many deserted mounds in 
the vicinity of Dos Cabezos, Ariz., in June, 1894, which may be 
accounted for in this way. In 1921 Vorhies found all mounds within 
4 or 5 miles of Albuquerque, N. Mex., deserted by spectahilis. result- 
ing probably from overgrazing by sheep and goats during a succes- 
sion of dry years. In the arid Southwest natural selection probably 
favors the animals with the largest food stores, and it is not surpris- 
ing that the storing habit has been developed to a remarkable degree. 
Some stored material is likely to be found at any time of year in 
any mound examined, the largest quantity usually in fall and winter, 
the smallest in July or August (Table 1, dens 1, 2, 14. and 24). 
Amounts found by different observers var}^ from a few ounces to 
several quarts or pecks, and stored materials taken from 22 mounds 
on the Range Reserve vary in weight from 5 to 4.127 grams 
(more than 9 pounds). This is exceeded by one lot from New 
Mexico, which totaled 5,750 grams (12.67 pounds). It is fairly 
evident that in seasons of scanty forage for stock the appropriation 
of such quantities of grass seeds and crowns and other grazing ma- 
terials by numerous kangaroo rats may appreciably reduce the carry- 
ing capacity of the range. Studies of cheek-pouch contents and food 
stores taken from dens show that the natural food of spectabilh 
consists principally of various seeds and fruits, particularly the seeds 
of certain grasses. The study of burrow contents has been especially 
illuminating and valuable. 
All of the stored material from 22 dens on the Range Reserve 
and from 2 near Albuquerque, N. Mex., has been saved and an- 
alyzed as to species as carefully as the conditions of storage would 
permit. Within the mound the food stored is usually more or less 
segregated by plant species, though the stores of material of any 
one kind may be found in several places through the mound, and 
often the material is mixed. In the latter case the quantities of 
the various species can only be estimated, but in the former the 
species may be kept separate by the use of several bags for 
collecting the seeds, and a fairly accurate laboratory weighing can 
be made later. Very frequently, the explanation of this separation 
of species lies in the different seasons of ripening, but sometimes 
where two species are ripe at the same time near the mound, one 
is worked upon for a time to the exclusion of the other. The one 
kind is often packed in tightly against the other, but with a very 
abrupt change in the character of the material. 
