THE GROUND SQUIRRELS OF CALIFORNIA. 



705 



7. The food preferences of ground squirrels are strongly in evidence 

 and vary from species to species, and sometimes within the same species, 

 from place to place and season to season. It is common testimony of 

 those who have practical experience in poisoning ground squirrels that 

 the Douglas is much more easily handled than the California ; in other 

 words, the former takes the strychnine-coated barley more readily. It 

 is obvious that the success of any method of control by the use of poison 

 must -depend importantly on the nature of the bait employed. The fact 

 that in some places the California Ground Squirrel has been found to 

 pass up barley altogether for the seeds of bur clover suggests a likely 

 way of improving poisoning methods locally. 



8. In the ' ' digger ' ' category of ground squirrels there is evidence that 

 a greater or less proportion of the population hibernates each winter. 

 In the Douglas this feature of the annual activity of the animal is 

 clearly evident, in that the majority, or at the higher altitudes all, of 

 the individuals disappear for weeks or months together during the 

 winter season. In the case of the California Ground Squirrel, however, 

 numerous individuals are to be seen aboveground in the lower country 

 in favorable weather at any time during the winter. But evidence at 

 hand goes to show that these active individuals are chiefly young of the 

 year and that most of the older squirrels are then lying dormant below- 

 ground, in some extreme cases for as long a period as from August to 

 February. During this interval, therefore, any method of poisoning, 

 and probably also of gassing, will obviously be ineffective upon a portion 

 of the population, and this portion which escapes will reappear at the 

 beginning of the next breeding season to reinfest the area concerned. 



9. Some obstacles to the success of control by the method of gassing 

 arise through the unequal extent and irregular course of the burrows 

 of the squirrels. It was found that although the volumetric content 

 of the burrows of the California Ground Squirrel excavated averaged 

 5.2 cubic feet, in one case an extreme of 17.8 cubic feet was reached. 

 This obtained in one of the ' ' colonial ' ' types of burrows in which several 

 establishments supposed to have been originally separate had come to 

 be intercommunicating. It was found that the usual dosage was ineffec- 

 tual in this case. There is no definite way of distinguishing such 

 4 'colonial" burrows, from surface appearances alone. Then, again, in 

 some burrows there is an abrupt rise in the underground course of the 

 burrow, which prevents the onward flow of a gas heavier than air, such 

 as carbon bisulphid, and the squirrel is not overtaken. In either of the 

 above circumstances we find a reason for the partial failure of extensive 

 gassing campaigns with current methods. 



10. Ground squirrels reproduce rapidly. In the California the 

 average number of young in a litter is 7.2, with 4 and 11 as extremes. 

 There is but one litter reared each year, and the young begin to appear 

 aboveground about the first of May. The sexes are equally divided in 

 a given population, and it is believed that each female breeds the first 

 season of her life, that is, when she is slightly less than a year old, and 

 that she has an "expectation" of rearing four more litters in case she 

 lives to die of old age. Thus a population of 10 per acre in March may 

 be expected to increase to 50 per acre by the last of May. Postponement 

 of attention by the farmer is a losing proposition. A stitch in time 

 actually saves nine. 



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