6 



NORTH AMERICAN FAUNA. 



[No. 40. 



The habits of the black-tailed species and, to a slightly less degree, 

 those of the more mountain-loving white-tailed forms, are decidedly- 

 social. The great size of the ''dog-towns'^ on the plains has indeed 

 been one of the principal subjects of comment by early travelers. 

 The villages sometimes extend for many miles and the number of 

 individuals inhabiting a big town is enormous. While in certain 

 localities the white-tailed species are almost as . gregarious as the 

 black-tailed forms, in others their dens are much more scattered 

 and the animals live in solitary families. These differences in habit 

 are due mainly to variations in local habitat. In certain parts of 

 the mountainous ranges of Cynomys gunnisoni and of C. leucurus, 

 the country is broken and otherwise unsuited to sustain large num- 

 bers of the animals, and the creatures necessarily live much as do 

 certain rock squirrels ,of the genus Citellus, in isolated pairs or widely 

 separated families. 



The prairie-dog is not strictly a hibernating animal except at high 

 altitudes or in the more northern regions where the great depth 

 of snow and the extreme severity of winter make hibernation a 

 virtual necessity. In the more southerly parts of the Great Plains 

 there is actually no period of hibernation. In the central Plains 

 States hibernation is partial and irregular, and even in the extreme 

 north the animals are not infrequently seen out on fine winter days, 

 though they hibernate for long periods during severe* weather. In 

 the higher mountainous habitat of the white-tailed forms the villages 

 are often covered for many weeks with a great depth of snow, and 

 activity on the part of the prairie-dogs is, therefore, out of the 

 question. In such regions the animals are rarely seen after November 

 or they may retire even by middle October. In the higher parts of 

 the New Mexican range prairie-dogs cease to appear above ground 

 by approximately the first of December, although, if conditions are 

 favorable, they are out on fine days throughout the winter. In the 

 Green River Basin, Wyoming, Vernon Bailey saw Cynomys leucurus 

 eating sage-brush tips on snow a foot deep in zero (Fahrenheit) 

 weather, and also after a night when the temperature had fallen to 

 22° below zero. 



The burrows vary greatly according to local necessities. In some 

 regions the mounds heaped up around entrances to dens are enormous, 

 while in others they are smaller or almost wanting. Much rainfall 

 necessitates high mounds, constant care, and incessant work by the 

 industrious animals until the safety of the home is insured. The 

 mounds in such cases are often especially well made and the earth 

 is very hard packed. Each double armful of wet dirt which is 

 pushed into position by the animal is rammed and packed into a firm 

 condition by repeated drives with the nose; the body, in curved 



