598 



THE MONTHLY BULLETIN. 



so successful when applied to the Oregon Ground Squirrel, which animal 

 apparently does not habitually gather and store seeds and grain to a 

 large extent, but is active chiefly during the spring and early summer 

 when green vegetation, upon which it depends for food, is to be had. 

 Some sort of green baits might be expected to be more effective with 

 this species. - 



It is very desirable at this time that we know more about the extent 

 of aestivation and hibernation among our ground squirrels. We know 

 little or nothing of the effect of gases upon squirrels in this condition; 

 and it is obvious that such part of a squirrel population as is dormant 

 at the time of a poison campaign will escape destruction and become 

 a nucleus of reinfestation. 



During the past spring and summer our work of excavating squirrel 

 burrows after the occupants had been gassed, has shown that one fre- 

 quent cause of failure in the ordinary waste-ball method of applying 

 carbon bisulphid is due to the fact that sudden elevation in the course 

 of the burrow, of as much as two feet in some cases, prevents the heavy 

 gas from reaching the animal. This condition was found to occur 

 much more frequently than is generally supposed. 



The instances just cited all suggest that the present knowledge of 

 our ground squirrels is far from complete, and they serve to emphasize 

 the above contention that a more thorough knowledge of this subject 

 is essential to securing the most intelligent and efficient methods of 

 control of these our chief rodent pests. It is the purpose of the present 

 paper to supply the information available from all sources in as much 

 detail as it has proven feasible for the authors to secure it at this time. 

 The facts and inferences are given just as they came, irrespective of 

 whether or not they show obvious and immediate economic bearing. 

 They are here available to everyone who is concerned with methods of 

 control. 



ACKNOWLEDGMENTS. 



The present paper has been prepared at the suggestion of Mr. G. H. 

 Hecke, California State Commissioner of Horticulture, and Mr. W. C. 

 Jacobsen, Superintendent of Rodent Control under this commission. 

 Both these men have rendered many valuable helps during the progress 

 of our work and have co-operated to facilitate its final publication. 

 Their emphasis all along has been upon the need of a summary of the 

 facts relative to rodent natural history at this particular time, when 

 efforts from every direction are being concentrated upon the problem of 

 increased crop production. j 



Upon the facilities and auspices of the Museum of Vertebrate Zoology 

 of the University of California the writers have been dependent for 

 the opportunity of carrying through their undertaking ; and behind this 

 has been the continual financial and moral support of the founder and 

 constant patron of the Museum, Miss Annie M. Alexander. The col- 

 lections of specimens and the field records contained in this Museum, 

 gathered during the past ten years, have been absolutely indispensable 



6 



