50 AN ECONOMIC STUDY OF FIELD MICE. 



100, insects; 5, spiders; 9, crayfish; 11, miscellaneous; and 43 were 

 empty. A good proportion of the " other birds " were English spar- 

 rows. About a third of the mice were identified as meadow mice, 

 while 24 were house mice. The large proportion of insects eaten is 

 remarkable. 



The burrowing owl (Speotyto cunicularia hypogcea) is a small 

 species, common on western plains, and noted for its abundance dur- 

 ing summer in prairie-dog " towns," where it occupies the deserted 

 burrows of that rodent. Of 32 stomachs of this owl examined by 

 Doctor Fisher, 2 contained mice; 1, a prairie dog; 3, lizards; 3, scor- 

 pions; 1, a centiped; 30, insects, and 1 was empty. The species is 

 largely insectivorous and undoubtedly highly beneficial. 



Several other species of owls occur in the United States, but at no 

 season are they abundant over any considerable area. Probably all 

 feed largely upon meadow mice. Doctor Fisher's report covered only 

 a small series; but 6 out of 9 great gray owl stomachs, 4 out of 22 

 sawwhet owl stomachs, 10 out of 38 snowy owl stomachs, and the 

 single hawk owl stomach examined contained the remains of field 

 mice. 



From the testimony of Doctors Fisher, Altum, Jackel, and Rorig, 

 and careful observations by others, the great value of owls for reduc- 

 ing the number of meadow mice is established beyond doubt, and the 

 various species should everywhere be protected by legal enactments. 



Among the most formidable bird enemies of field mice are the larger 

 members of the crow family (Corvidce). The fact that ravens, 

 hooded crows, and rooks in the Old World feed upon voles and lem- 

 mings has often been noted. American crows have similar habits 

 and feed upon field mice wheneA T er occasion offers. Besides the 

 common crow (Oorvus brachyrliynchos) the list of mouse-eating 

 crows includes the fish crow (Corvus ossifragus) , the northwest crow 

 (Oorvus b. caurinus), the raven (Corpus corax sinuatus), and the 

 white-necked raven (Core us cryptoleucus). Magpies and the larger 

 jays also destroy mice to some extent. 



The food habits of the common crow form the subject of Bulletin 

 No. 6 of the Biological Survey. The results of examinations of 

 909 stomachs of crows are tabulated in the report. Of this number, 

 78 contained mice, they being fourth in order of importance on the 

 list of animal food for the year. Professor Barrows says : " There 

 is abundant proof from several sources that crows often capture 

 living mice, particularly the short-tailed field mice, which build their 

 nests usually on the surface of the ground among the roots of grass. 

 Here the crows discover them, and, tearing the nest to pieces, cle- 



o The Common Crow of the United States, Walter B. Barrows and E. A. 

 Schwartz, 1895. 



