BUKEAU OF BIOLOGICAL SURVEY. 661 



of poisoned grain, by which a majority of a colony are killed while 

 feeding outside the burrows. As, however, in every colony there are 

 a certain number which for one reason or another escape it is neces- 

 sary, after poisoning operations, to treat with carbon bisulphid or 

 pintsch oil the burrows still occupied. The efficiency of these two 

 agents is about equal, but our experiments have shown that when 

 pintsch oil is obtainable it is probably the cheaper of the two agents. 

 It is worth noting that early in the spring snow can be employed 

 effectively to stop up the burrows during the bisulphid or pintsch 

 oil operations. These experiments have demonstrated also that oats 

 are the best vehicle for carrying poison, as they are readily eaten 

 by prairie dogs and are rarely eaten by birds, 



THE CALIFORNIA GROUND SQUIRREL. 



Smaller than the prairie dog, this rodent ranges over much of 

 California, and thrives equally in mountain, foothill, and valley. It 

 is a voracious feeder; and as its aggregate numbers are enormous, 

 its capacity for destroying forage and crops is almost unlimited. 

 AVhile the complete extermination of the animal within the State 

 may be long deferred by reason of the cost, a very material reduction 

 vi its numbers, at least in cultivated districts, can be effected at an 

 expense which would be justifiable on purely economic grounds. The 

 fact that this animal has been infected with plague by fleas from 

 rats and that this dread disease is hence likely to become endemic in 

 California furnishes a vastly more important reason for the destruc- 

 tion and one that bears directly on national health problems. Under 

 the present State law requiring citizens to clear their holdings of 

 squirrels, and through cooperation wdth the Public Health Service, 

 much has been effected by State authorities, but the public domain 

 within the National Forests remains practically untouched. A small 

 fund having been made available, the Survey will begin the work of 

 reducing the number of these rodents within the California National 

 Forests. Meantime, during the past year experiments have been con- 

 ducted with poisoned baits, so that it is believed a maximum amount 

 of good can be accomplished with the funds placed at the disposal 

 of the Survey at a minimum of cost. 



GOPHERS, 



Though comparatively small, the several species of gophers are 

 difficult to destroy, owing to the fact that they live almost entirely 

 underground. Numerous experiments have shown that these ani- 

 mals are not difficult to trap, but when employed on a large scale 

 this method, though effective, is attended with considerable expense. 

 Hitherto it has been found difficult to poison pocket gophers; but 

 during the past winter many poisoning experiments were carried on 

 with very promising results in California, where the animals are par- 

 ticularly destructive in truck farms and orchards. In many locali- 

 ties these animals were almost exterminated over considerable areas 

 by the use of sweet potatoes covered with the strychnine-starch solu- 

 tion which has proved .so effective in destroying prairie dogs. 



