THE GROUND SQUIRRELS OF CALIFORNIA. ' 635 



uncultivated land where they are least molested through human agency, 

 and from this they spread out and invade nearby cultivated fields. 

 The process is most conspicuously in evidence during late summer con- 

 sequent upon the emigration of the young of the year, this being in 

 compensation for the tendency to congestion of population brought on 

 during the breeding season. 



Reduction in the food supply locally causes the squirrels to spread 

 out in search of new pastures. Such movements are usually less than 

 a mile in extent, and of course come particularly to notice in the vicinity 

 of grain fields and orchards to which the squirrels drift at the time the 

 crops begin to ripen. Some idea of the rate with which ground squirrels 

 reinfest cultivated fields which are adjacent to wild land may be had 

 from the following instance. Mr. 0. N. Garrison of Earlimart, Tulare 

 County, stated in an intervicAV that during the spring of 1918 thirty-six 

 ground squirrels were drowned out on a five-acre field of alfalfa at the 

 first irrigation and this in spite of the fact that the field had been free 

 from squirrels at the end of the previous irrigation season in the fall 

 of 1917. 



From the earliest times of which we have record to the present day 

 the California Ground Squirrels have given the impression of abun- 

 dance. Changes in the status of the species within history have only 

 concerned local occurrence. There is nothing to show that there has 

 been any extension of the general range of the species, or any retraction 

 in it either. As already set forth, the arrival of the white man and the 

 institution of agriculture has undoubtedly had the effect locally of 

 increasing the ground squirrel population. On the other hand, where 

 man has been aroused by the seriousness of their depredations to the 

 point of adopting and putting into force effective means of control the 

 numbers of the squirrels have been conspicuously reduced. Thus at 

 Earlimart on May 16, 1918, ground squirrel burrows were found to be 

 abundant over a large acreage of "hog wallow" land. Live squirrels, 

 however, were exceedingly scarce, only five being found on one tract of 

 forty acres which had been thoroughly poisoned the previous season. 

 A count taken on this tract showed that there was an average of fifty 

 empty burrows to each squirrel present. 



A very few localities have been reported in which the squirrels are, 

 for the time being at least, things of the past; but the possibility of 

 re-invasion presents itself, and this, as already shown, may be a very 

 rapid process. It would seem that ground squirrels, like weeds or 

 scale bugs, will have to be watched continually, and proper measures 

 taken whenever necessary to prevent the reinfestation of land which is 

 thought to have been freed. 



The difficulties in arriving at a fair estimate of the damage done by 

 the California Ground Squirrel, which is by far the most injurious 

 species in the state, are many and various. We have tried to get at 

 a satisfactory estimate (not a guess) in terms of dollars per annum, 

 but have not succeeded. It may be of some interest, however, to give 

 some other figures, indicative in partial degree of the loss that may be 

 occasioned by this ground squirrel. 



In order to ascertain the bearing of squirrels upon grazing interests 

 we have found some basis for estimating squirrels in terms of live- 

 stock. We have weighed and examined the stomach contents of a series 



