THE GROUND SQUIRRELS OP CALIFORNIA. 



711 



proposed to designate the yards and cabins in which the genus Citellus 

 was to be studied (Fig. 31). 



Fig. 31. The Citellary, comprising yards enclosing' natural, wild squirrel dens. 

 One of these yards is 50 by 90 feet in extent. Associated with the yards are 

 cabins in which brooding and hibernating squirrels were studied. Here squirrels 

 lived almost in freedom. 



THE CITELLARY. 



In the construction of these yards five adjoining squirrel dens were 

 selected. These were located on a warm sunny southwest slope, and 

 were covered with an abundant wild vegetation of bunch grass, balsam- 

 root and rose brush. Here fences were sunk in the ground to a depth 

 of six feet and arranged to enclose yards of ample size (50' by 90' in 

 one case). Two small cabins were constructed, one for the close study 

 of breeding squirrels (Fig. 32) and one for the observation of those in 



Fig. 32. The breeding cabin. In this building were brood nest boxes, con- 

 nected with yards enclosed with wire netting. During all their confinement in 

 these small yards, the developing squirrels could be observed by simply lifting 

 the hinged lid to the brood-nest-box. 



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