712 



THE MONTHLY BULLETIN. 



hibernation. In these yards wild squirrels were turned, after first 

 having been weighed, branded, and recorded. Here they lived in semi- 

 freedom, yet largely subject to the will of the investigator, giving to 

 the study many facts otherwise unobtainable, verifying, too, many of 

 the observations made in the fields. With these preparations com- 

 pleted, work was begun in earnest. 



ACTIVITIES. 



Both in the field and in the citellary it was learned that the animals 

 were very markedly diurnal, very responsive to sunlight and warmth, 

 and avoided the effects of cloudy days, cold winds and wet weather. 

 In the matter of their daily activities, they appeared about an hour 

 after sunrise, and were all in their dens at sunset or shortly thereafter. 

 During the day they were most abundant about 9 to 10 o'clock in the 

 morning and avoided the intense heat of the midday sun. 



THE DEN. 



A little careful observation in the field soon showed that the squirrels 

 were living in a definite series of radiating burrows called a den 

 (Fig. 33). These proved to be units and though long, careful exam- 

 inations were carried on, in which more than 150 dens were excavated, 

 in no case were these dens found to communicate underground. That 

 they were visited freely by squirrels above ground, at certain seasons, 

 was apparent from the fact that well-worn paths were observed leading 

 from one den to another. 



Hijh Side. oj/Jten. 



Fig. 33. A typical squirrel den. The total length of open burrow in this den 

 is 63 feet 8 inches. The average depth of the burrows is 2 feet. The greatest 

 depth is 2 feet 6 inches. The average diameter of the burrow is 3.5 inches. 

 (From Popular Bulletin No. 99, Washington Experiment Station.) 



The den itself was made of a series of radiating burrows from a 

 common center as shown in figure 33. These burrows were about 

 three and one-half inches in diameter except at their intersections, where 

 they were slightly larger, and were on an average of two feet below 

 the surface. Some burrows in. deep soil were found as deep as five feet. 



120 



