GROUND SQUIRRELS 105 



ground to a greater or less degree, as indicated by the fact that when 

 hurriedly seeking safety squirrels will pitch down into any one of a 

 number of holes in the vicinity of the one about which they were first seen, 

 to reappear later somewhere else. Also, squirrel exterminators, when using 

 gases or smoke in their work, find it necessary to stop up a number of holes 

 adjacent to the one into which they introduce the fumes in order to force 

 them into the lower reaches of the tunnels. 



The burrows of the squirrels are often inhabited by species of animals 

 other than the rightful owners. The so-called Burrowing Owls habitually 

 make their homes in squirrel holes, probably deserted ones; and, to a 

 less extent, the holes are frequented by California Toads, Western Gopher 

 Snakes, and Pacific Rattlesnakes. It is likely that the presence of the 

 latter two animals is not particularly congenial to the squirrels, as both 

 of these snakes are known to eat ground squirrels when chance offers. 



The burroAving activities of the California Ground Squirrel constitute 

 a matter of considerable economic importance. The Yosemite Valley Rail- 

 road Company has found it necessary to reduce the numbers of the ground 

 squirrels along its right of way through the lowlands ; for the burrows of 

 the animals weaken the grade embankments and, especially in wet weather, 

 cause them to give way. The company has learned that the results obtained 

 by their anti-squirrel campaigns fully justified the expenditure entailed. 

 Also, ranchers in the irrigated districts near Snelling patrol their ditches 

 so as to discover and promptly plug up any and all squirrel burrows made 

 in the banks, thereby preventing breaks, with consequent loss of the 

 precious water. 



Some years ago it was discovered that the ground squirrels in California 

 were harboring fleas which carried the bacillus of bubonic plague. A 

 vigorous campaign of extermination was waged against the animals and 

 they were practically eliminated from many extensive areas. As soon as 

 the efforts against the squirrels were relaxed, however, they began to 'spill 

 in' from adjacent areas until now in most places they are as numerous 

 as ever. 



Ranchers living in the mountains find difficulty in keeping their 

 meadowlands rid of squirrels. Mr. W. H. McCarthy, whose ranch is 3 

 miles east of Coulterville, told us that a regular patrol was necessary to 

 keep his fields even approximately free. On the floor of Yosemite Valley 

 attempts at poisoning ground squirrels have been made at various times 

 during the past decade, but no appreciable diminution in their population 

 was observable as a result of this work. In May, 1919, the squirrel popu- 

 lation of the Valley appeared to be the largest of any of the years for which 

 we have record. 



