240 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



or 6 drops of carbon bisulphide into each burrow by means of a 

 long-nozzled oil can and closing the opening by pressure of the foot. 



SEED-EAIING RODENTS. 



Extermination of rodents which destroy seeds and nursery stock 

 on areas that are being reforested has been completed on the Black 

 Hills National Forest of South Dakota and the Florida National 

 Forest of Florida, and experiments have been conducted on the above 

 planting areas and on the Converse Experiment Station of Califor- 

 nia. Improved methods for controlling pine mice, wood rats, and 

 other seed-eating rodents have been discovered. 



FUR-BEARING ANIMALS. 



Investigations of the behavior and requirements of minks and 

 martens in confinement have been continued at Linden, Md., and 

 the National Zoological Park, D. C. Inexpensive types of pens have 

 been devised which are proving very satisfactory. Effects of rations 

 differing in composition and amount have been studied in relation to 

 breeding, fur production, and general health. An understanding of 

 the symptoms and causes of the common ailments of these animals 

 has been gained, and remedial or preventive measures have been 

 adopted. The results attained with these animals and the numerous 

 requests for advice about fur farming have prompted the establish- 

 ment of an experimental fur farm in northern New York, under 

 conditions favorable to the production of high-grade fur and to the 

 development of practical fur farming. Here experiments may be 

 undertaken on a much larger scale than has hitherto been attempted. 

 It is expected that, ultimately, many kinds of fur animals, foreign 

 as well as native, will be tested as to their adaptability to domestica- 

 tion. One of the most important lines of work to be taken up will 

 be that of developing improved strains by selective breeding. Yards, 

 pens, an ice house, and a storehouse are being erected and soon will 

 be ready for use. 



An assistant spent the summer of 1915 in Alaska investigating 

 the present status there of fur farming, and the special needs of 

 those engaged in it. It appears that upward of 100 Alaskans are 

 directely interested in the domestication of fur animals. In 35 lo- 

 calities there are silver-fox yards, and on an equal number of islands 

 blue foxes are farmed. The silver-fox farms are not yet producing 

 fiir, but pelts sent to market this season from the older blue-fox farms 

 brought gratifying returns. 



During the year two bulletins concerning fur-bearing animals 

 were published, one being a summary of laws in the United States 

 and Canada relating to trapping, protection, propagation, and boun- 

 ties; and the other a bulletin on silver-fox farming. 



FOOD HABITS OF THE THRUSHES. 



A report on the thrushes, completed and published during the year, 

 shows that the economic tendencies of these birds are in keeping with 

 their other desirable qualities. The 6 species discussed are found to 

 commit no depredations on crops, but to destroy large numbers of 

 insects, including some that are very injurious. 



