REPORT OF THE SECRETARY. 81 



rental to the trappers is usually for half the fur, leaving the meat 

 as an additional source of gain to them. Only one other animal in 

 the world, the European rabbit, exceeds the muskrat in the number of 

 skins marketed. 



RODENTS IN RELATION TO AGRICULTURE. 



Prairie dogs, ground squirrels, and gophers are very destructive 

 rodents, inflicting large damage and levying a heavy tax upon the 

 tillers of the soil; therefore the Biological Survey conducts experi- 

 ments with poison baits, traps, and other methods of extermination. 



The daily forage consumed by 32 adult prairie dogs equals the 

 amount required by a sheep, and 250 eat approximately as much as a 

 cow. The ground squirrel, though smaller, is a voracious feeder, and 

 the gophers, comparatively small, are not abstemious. As the region 

 infested by these pests includes a number of Eocky Mountain States, 

 California, and other Western States, and as some of the colonies 

 occupy many thousand acres and aggregate millions of rodents, the 

 extent of the damage they do to forage and other farm crops can be 

 readily comprehended. 



Besides, it has been definitely ascertained by the investigations of 

 the past two years that the spotted-fever ticks, in the two younger 

 stages, live almost wholly on small native rodents, and that the 

 California ground squirrel has been infected with bubonic plague 

 by fleas from rats, hence that these dread diseases are likely to become 

 endemic. Therefore there are two important reasons for attempting 

 the extermination of the animals. The chief reliance for this is 

 placed on the use of poisoned grain and other poisoned baits, but 

 the use of traps, and, in some cases, the use of carbon bisulphid or 

 pintsch oil in the burrows, supplements the poison. In these ex- 

 periments oats have been found to be the best vehicle for carrying 

 poison, as it is readily eaten by the rodents and rarely by birds. 



THE ECONOMIC RELATIONS OF BIRDS TO FARMING. 



Investigations by the bureau, in cooperation with the Bureau of 

 Entomology, as to the relations of birds to the insect to determine 

 what aid, if any, birds are likely to lend in checking the increase of 

 the alfalfa weevil and retarding its spread, show that although the 

 weevil has been established in this country only five or six years 31 

 species of birds have already learned to eat it. It is an interesting 

 discovery that the English sparrow heads the list as a determined foe 

 of the weevil, and that, if it is possible to utilize the services of the 

 English sparrow against the formidable insect foe, the alfalfa weevil, 

 it will be part compensation for the damage done by that bird in other 

 sections. 



704S1°— AGB 1912 



