In May, 1894, Fisher found a ranchman at Willcox, Ariz., who complained
more bitterly of the depredations of _spectabilis_ than of those of any
other mammal.
On the United States Range Reserve the food material appropriated by the
kangaroo rat during good years is inappreciable. There is such an excess
of forage grass produced that all the rodents together make very little
difference. But with the periodic recurrence of lean years, when drought
conditions are such that little or no grass grows, the effects of rodent
damage not only become apparent, but may be a critical factor
determining whether a given number of domestic animals can be grazed on
the area (Pl. VIII, Fig. 2).
With two kangaroo rats to the acre (1,280 per square mile), there would
be 64,000 animals on the 50 square miles of the Range Reserve. If each
rat stores 4 pounds of grass seeds and crowns and other edible forage
during the season (and in severe seasons we find that more crowns are
stored than under ordinary conditions), a total of 256,000 pounds, or
128 tons, of edible forage are rendered unavailable to stock. In dry
years it is probable that this amount of forage would be of critical
importance. Allowing 50 pounds of food a day for each steer, the forage
destroyed would be sufficient to provide for the needs of one steer for
5,120 days, or for the needs of 14 steers for one year. On a stock ranch
the size of the Range Reserve this might mean the difference between
success and failure.
It seems not unlikely, therefore, that during seasons of drought the
banner-tailed kangaroo rat, where it is abundant on the grazing ranges
of the Southwest, may be a factor of critical importance in relation to
forage production and carrying capacity. It must be remembered,
moreover, that the stored material consists largely of seeds, so that
this loss is of greater importance than would be the case were it
ordinary forage. Some of the range grasses of this region found in
greatest quantity in the stored material depend in large part, under
certain conditions, upon seed reproduction. Rehabilitation of a depleted
range after severe drought and consequent close grazing and trampling is
retarded by the heavy toll of seed taken by the kangaroo rats.