284 ECONOMIC MAMMALOGY 



grain. When abundant about orchards or ornamental shrubbery it some- 

 times does damage by girdling. 10 



The field or meadow mice, genus Microtus, are the most abundant 

 mammals of North America, except the white-footed mice (genus 

 Peromyscus). They are very prolific, having from 2 to 6 litters of 

 from 6 to 13 young, per annum. 11 Consequently they are a constant 

 menace to agriculture as they may increase very rapidly when condi- 

 tions are favorable, and overrun large areas, destroying all crops and 

 forage. During an outbreak of field mice in Nevada in 1907 it was 

 estimated that there were 12,000 mice to the acre, and in some fields 

 they completely destroyed the alfalfa, roots and all. 12 In a meadow, 

 1000 mice require 12 tons of grass or other vegetation in a year. 13 



Mouse outbreaks may to some extent be avoided by constant watch- 

 fulness and prompt measures for suppression as soon as an increase 

 in their numbers is noticed, and damage from the girdling of trees may 

 be minimized by keeping orchards and land adjacent thereto clean and 

 free from weeds, grass and other shelter, especially in winter, when 

 they are more likely to attack trees. 14 As these mice feed mostly above 

 ground, mechanical and chemical protection, such as wire screens and 

 repellent washes, aid in preventing damage to trees. 15 Among the 

 natural enemies that habitually destroy mice are wolves, lynxes, coy- 

 otes, foxes, badgers, raccoons, opossums, skunks, weasels, shrews, cats, 

 dogs, hogs, hawks, owls, shrikes, cuckoos, crows, herons, bitterns, 

 storks, ibises, gulls and snakes, 16 yet many farmers and hunters kill 

 those bird and mammal enemies of mice at every opportunity. Snakes 

 are cold-blooded, their digestion is slow and they require but little food, 

 hence are not of great value as mousers. 17 



The fluctuations in the field mouse population affects other human 

 interests besides agriculture and horticulture. When they are abundant 



10 Bailey, N. Amer. Fauna, No. 49, p. 88, 1926. 



11 Piper, The Nevada mouse plague of 1907-08, Farmers' Bull., No. 352, 1909; 

 Mouse plagues : Their control and prevention, Yearbook U. S. Dept. Agric. for 1908, 

 p. 303. Hatt, The biology of the voles of New York, Roosevelt Wild Life Bull, v, 

 513-623, 1930; discusses food stored, enemies, damage to crops, trees, destruction 

 of insects by, mouse plagues, protection of trees from. 



12 Bailey, Farmers' Bull. No. 335, p. n, 1909. Piper, Farmers' Bull., No. 352, 1909; 

 Yearbook for 1908, pp. 301-310. 



13 Lantz, An economic study of field mice, U. S. Biol. Surv. Bull. 31, 1907. 



14 Birdseye, Farmers' Bull. No. 484, 1912. 



15 Silver, Mouse control in field and orchard, Farmers' Bull., No. 1397, 1924. 

 16 Lantz, An economic study of field mice, U. S. Biol. Surv. Bull. No. 31, pp. 



38-53, 1909. 



"Burnett, Office Colorado State Entom., Circular No. 25, p. 31, 1918; No. 18, 

 p. 7, 1916. 



