258 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 
The prairie dog loves sunshine and a dry atmosphere, and in ranging 
easterly from the arid plains toward the humid prairies of the Missis- 
sippi Valley becomes less and less numerous, till between the ninety- 
seventh and ninety-eighth meridians he disappears altogether. Not 
even the luxurious vegetation of the prairies is sufficiently attractive 
to lure him into the humid belt adjoining his chosen home. That he 
is fond of rich vegetation and prefers it to the dry bunch grass of the 
plains is shown by his great destructiveness to alfalfa, grain, and 
other crops grown on irrigated lands within his range. This is an 
important illustration of the law that in lixing the limits of distribu- 
tion of animals climatic factors are even more potent than food. 
The prairie dog is preeminently a social animal, living in colonies 
which vary in extent from a few acres to thousands of square miles 
and inhabited by thousands, and in some cases millions, of animals. 
Colonies 20 to 30 miles in length are not rare, and in Texas one is 
known which measures about 250 miles one way by 100 to 150 the 
other, covering an area of about 25,000 square miles. The number of 
holes in use on each acre varies from a few to upward of a hundred, and 
probably averages at least 25. At Alma, Nebr., W. H. Osgood found 
the number ranging from 35 to 64, and on an alfalfa held near Carls- 
bad, N. Mex., Vei-non Bailey found 1,009 on 20 acres, or 50 to the 
acre. In old towns many holes are abandoned, or used only as refuges, 
so that it is difficult to ascertain how many animals live in a stated 
number of holes. Another difficulty lies in the varying number of 
animals in the occupied holes, for in winter and early spring the usual 
number is two (a pair), while after the birth of the young the number 
is at least quadrupled, and then decreases with the advance of the sea- 
son, as the young are killed by enemies. It is certainly a conservative 
estimate to assume the average number of animals per acre to be 25. 
On this assumption, the number of prairie dogs in the great Texas 
colony must be at least 400,000,000. 
According to the formula for determining the relative quantities of 
food consumed by animals of different sizes (kindly given me b}^ Prof. 
W. W. Cooke), 32 prairie dogs consume as much grass as 1 sheep, and 
256 prairie dogs as much as 1 cow. On this basis the grass annually 
eaten by these pests in the great Texas colon}^ would support 1,562,500 
head of cattle. Hence, it is no wonder that the annual loss from 
prairie dogs is said to range from 50 to 75 per cent of the producing 
capacity of the land and to aggregate millions of dollars. 
GENERAL HABITS OF PRAIRIE DOGS. 
When a person approaches a dog town the animals see him a long way 
off and keep a close watch on his movements. As he comes nearer an 
alarm note is sounded, at which those awav from their burrows rush to 
the entrance mounds, where they sit or stand erect, nervously twitching 
