42 AN ECONOMIC STUDY OF FIELD MICE. 



row or shock. While they seldom eat rats or house mice, they some- 

 times become very fond of field mice and learn to hunt them inde- 

 pendently. A good rat dog is undoubtedly a valuable asset of the 

 farm, and I have known one to keep premises clear of brown rats 

 {Mns norvegicns) when adjoining farms were overrun with them. 



Many cats are good mousers, both in house and field. Some live 

 largely upon pocket gophers, ground squirrels, and field mice. Un- 

 fortunately, however, when cats roam afield they learn to destroy 

 song birds, young poultry, and game. The ordinary farm cat is 

 exceedingly destructive to small birds and game, and the number that 

 cats annually kill is immense. 



House cats usually are too well fed to make good mousers, and 

 are believed to aid in the spread of infectious diseases among human 

 beings. In spite of the usefulness of individual cats in destroying 

 mice, every community would be better off for a large reduction in 

 its feline population. 



Birds that Destroy Field Mice. 



Many species of birds destroy rodents. Among those that eat field 

 mice are shrikes, cuckoos, crows, herons, bitterns, storks, ibises, 

 gulls, hawks, and owls. Unlike the mammals already named, some 

 of these birds live almost exclusively upon field mice, and hence are 

 of great assistance in reducing their numbers. 



BIRDS OF PREY. 



At the head of the list of bird enemies of field mice stand the 

 hawks and owls. Most of the species habitually feed upon rodents, 

 a feAY of them almost entirely. Moreover, the species that feed least 

 upon harmful rodents feed largely upon insects. Thus the beneficial 

 character of hawks and owls as a group is beyond question. 



Fortunately the economic status of American hawks and owls 

 does not rest upon mere theory or general assertions without proof. 

 Bulletin No. 3 of the Biological Survey a deals with the food habits 

 of hawks and owls of the United Staters, and is based upon examina- 

 tions of nearly 2,700 stomachs. Such large series of the more com- 

 mon species were examined that further investigations can but con- 

 firm and emphasize the present verdict — that American hawks and 

 owls, as a whole, are among the best friends of the farmer and that 

 only a few species are more harmful than beneficial. 6 



a The Hawks and Owls of the United States in their Relation to Agriculture, 

 by A. K. Fisher, M. D., Washington, 1S93. 



6 Doctor Fisher's report on the food of hawks and owls has long been out of 

 print. For this reason some of the more important summaries of results, 

 especially those relating to the mammal food, are given in this paper. Circular 

 61, Bureau of Biological Survey, Hawks and Owls from the Standpoint of the 

 Farmer, gives a brief summary of the original report by Doctor Fisher, and 

 may be had on application. 



