48 



AN ECONOMIC STUDY OF FIELD MICE. 



Essex, in 1581, by saying: "Which vermin by policie of man could 

 not be destroyed, till at the last there flocked together such a number 

 of owles as all the shire was not able to yield, whereby the marsh 

 holders were shortly delivered from the vexation of the said mice." 

 Similar testimony as to the efficiency of owls as destroyers of voles 

 is contained in other chronicles, and in the account of later out- 

 breaks the species is definitely stated to be the short-eared owl. 



The short-eared owl inhabits the temperate parts of both conti- 

 nents. In each its range extends northward well beyond the Arctic 

 Circle. It is an irregular migrant and always appears in large num- 

 bers where voles, lemmings, or other mice become unusually abun- 

 dant. It nests on the ground in tall grass, usually in moist meadows, 

 a habitat peculiarly fitted for the operations of this consumer of 

 meadow mice. Doctor Fisher reports the results of examinations of 

 101 stomachs of this species. Of these, 11 contained small birds; 

 77, mice; 7, insects: and 14 were empty. In the 77 stomachs that 

 contained mice fully a hundred field mice Avere identified. Doctor 

 Rorig examined 51 stomachs of this species and found in them re- 

 mains of 1)0 injurious rodents, of which 76 were Microtus. He ex- 

 amined also 480 pellets of this owl, finding remains of 3 beetles, 9 

 small birds. 7 bank voles, 22 Microtus agresth^ and 842 M. anxilis. 



For purposes of comparison, tlie results of the examinations of owl 

 pellets are here presented in tabular form. The figures, disregarding 

 fractions, represent the average number of individual mammals and 

 birds found in 100 pellets of each species of owl. 



Kind of mammal or bird found 

 in owl pellets. 



Harmful rodents : 



Mus (rats and mice i 



Microtus (field mice; 



Other rodents 



Insectivorous mammals (shrews 



moles, and bat«) 



Small birds (sparrows, etc. ) 



10 



182 



a 8 



1 



be 



o 



2 

 168 

 a2 



3 

 1 





la 



5 ^ 



o 



QD 







180 

 al 





 •) 



"Bank voles (Evotomyg). 



b Not given . 



The barred owl {Syrnium carium) is larger than the species 

 already considered. It resides throughout eastern North America 

 from Nova vScotia to the Gulf and westward to the treeless plains. 

 It usually lives in rather dense forests and swamps and nests in hoi- 



