714 



THE MONTHLY BULLETIN. 



The seasonal breeding season is dependent especially upon the 

 elevation ; they appearing from hibernation and breeding early at low 

 altitude (Wawawai, Washington, elevation 600 feet), and later at high 

 altitudes (Cedar Mountains, Idaho, elevation 4,000 to 5,000 feet), 

 although these elevations were not over 30 or 40 miles apart. What is 

 more remarkable is the fact that on the north and south slopes of the 

 hills about Pullman the dates for these activities varied by about seven 

 to ten days, although the hills are not much over 300 feet in elevation 



Fig. 35. Six days old. In the interval the squirrels shown in Figure 34 have 

 doubled their original weight. 



Fig, 36. Twelve days old. At this age they have become quite dark on the dorsal 

 side owing to the developing of hair roots. 



122 



