ANIMAL BEHAVIOR — WALKER 289 



the animals to survive in rigorous climates through periods when 

 food is generally very scarce. 



In the northern portion of their range, the prairie dogs (Cynomys) 

 make a complete and long hibernation, that is to say, they go to sleep 

 in the fall and do not come out until spring. Farther south they 

 come out during the winter if the weather is unusually mild ; and in 

 the southern portion of their range they scarcely hibernate at all. 

 Prairie dogs, it must be remembered, are not dogs at all. They are 

 burrowing squirrels closely related to marmots (Marmota). 



Woodchucks {Marmota) are, of course, noted for their habit of 

 sleeping through the winter. While their movements on February 

 2 are of absolutely no importance in indicating the kind of weather 

 to be expected during the following 6 weeks, much popular interest 

 is taken in the springtime emergence of these animals. 



Skunks in the north remain in their dens all winter and are fre- 

 quently not to be seen for days or even weeks during the worst 

 winter weather. During these periods they are almost in hiberna- 

 tion. However, a slight moderation of the weather will bring them 

 out ; so theirs is only an incomplete hibernation. 



Many rodents not only hibernate but go into estivation in mid- 

 summer or late in the summer. In many cases it continues into the 

 winter sleep. Notable among these estivating rodents are a number of 

 species of Spermophiles or ground squirrels {Citellus and Sperm- 

 ophilus) of the western United States that put on fat during the early 

 summer when food is abundant and temperatures are favorable. In 

 the hottest portion of the summer when food in some cases has be- 

 come scarce they go to sleep in burrows deep enough in the ground 

 so that the temperature does not affect them and they do not have 

 to worry about the drought or the food supply. Some individuals 

 emerge for a short time in the late summer or early fall but many 

 of them continue their summer sleep into that of winter. 



The pocket mice and kangeroo rats go into hibernation as soon 

 as the weather is a little chilly in the fall and remain curled up in 

 little furry balls for months at a time. Tliey do not emerge until 

 the weather has become warm. Apparently a temperature of about 

 50" to 60° will cause some of them to hibernate. 



The common chipmunks {Tamias and Euta/mias) that are so con- 

 spicuous during the summer do not truly hibernate through most of 

 their range. They merely stay under shelters and in their homes. 

 When the weather is severe or inclement they must feel like many 

 people, sleepy and loath to go out. 



In the 1910 edition of the Encyclopedia Britannica it is stated that 

 in some of the northern Provinces of Russia where food is very scarce 

 and the winter climate severe, the people have adopted a mode of 



