SUMMARY OF POINTS OF SPECIAL IMPORTANCE FROM THE STANDPOINT OF GROUND SQUIRREL CONTROL.
From the foregoing account of the natural history of the ground squirrels of California the following facts and inferences stand out as seemingly of special importance in connection with the determination and application of methods of ground squirrel control.
1. Of the eighteen kinds of ground squirrels occurring within the limits of the state, there appear to be only four meriting any particular consideration from an economic standpoint. These four are the California (or Beechey), the Oregon, the Fisher and the Douglas ground squirrels, here named in the estimated order of importance (see fig. 30). All the other fourteen kinds are, for the present at least, negligible, in most of the cases because they inhabit areas not cultivated by man.
2. The Oregon Ground Squirrel is less than half the size of a "digger" squirrel, but it is ordinarily present in much greater numbers per given area within its range (most of Siskiyou, Modoc and Lassen counties) than is any one of the "digger" squirrels in its range. The Oregon inhabits open grass lands and hence comes into sharp competition with cattle interests.
3. The Oregon Ground Squirrel is more of a grass eater than a seed or grain eater, and the most successful method of poisoning should involve the selection of an appropriate bait accordingly. It does not store up food to the extent that the "digger" squirrels do. The Oregon Ground Squirrel, more than any of the "digger" category, is subject to a sharply defined period of hibernation, and this involves all the individuals, of whatever age.
4. The California Ground Squirrel is our species of greatest aggregate numbers and is the one which is most widely distributed over the cultivated parts of the state. Its close relatives, the Fisher and Douglas ground squirrels, are known along with the California as "digger" squirrels; regarding most of the following considerations the three may be classed together.
5. Because of relatively large size the individuals of the "digger" category are able to inflict serious loss. Adults average 1¼ to 1½ pounds in weight, and are easily able to consume ½ ounce of dry grain or 2 ounces of green forage at a meal.
6. On open range and pasture lands these squirrels feed largely on alfilaria and bur clover, two of the most valuable forage plants in the state. The squirrels are then serious competitors for subsistence against the flocks and herds upon which man depends for his own support. On cultivated ground these squirrels feed upon or destroy in other ways grain and fruit crops to a very large extent where present even in numbers not above those reached on wild land. The tendency seems to be to increase to extraordinary numbers on cultivated lands unless effectively checked by man. This is due both to improvements of food conditions from the standpoint of the squirrel, and to removal of its natural enemies by man either purposefully or thoughtlessly.
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