38 ECONOMIC MAMMALOGY 



wise destroying rats, fumigating ships, rat-proofing buildings and in 

 various other ways seeking to prevent damage by rats, fires caused by 

 rats and the relation of these rodents to public health. Fisher says that 

 rats "kill more young chickens than any other animal." 5 Following 

 this indictment we may add that the house rat has no redeeming 

 feature. Unlike rabbits, for example, its destructiveness is not to any 

 real extent recompensed by its value as food. 



Wood rats are not as a rule abundant enough to do much damage, 

 but some species in certain localities become very abundant and do 

 much damage to gardens and along the edges of grain fields. In Ore- 

 gon they have been known to damage fruit trees by gnawing the bark. 6 



In districts where they occur, pocket gophers are considered among 

 the most injurious of our native mammals, the annual loss caused by 

 them to farmers and fruit-growers of the United States having been 

 estimated at over $i2,ooo,ooo, 7 $1,000,000 for Nebraska alone. 8 



The house mouse, already mentioned in connection with the house 

 rat, is a great pest and does a large amount of damage by the destruc- 

 tion of grain and other foodstuffs in granaries, stores, warehouses and 

 dwellings, as well as by injury to many other commodities. It is also 

 a potential menace as a field pest. This is well illustrated by a recent 

 house mouse plague in California, when they swarmed over the fields 

 of Kern County at an estimated frequency of 82,000 to the acre, do- 

 ing great damage to crops. 9 Because of their fecundity, various other 

 species of mice, under conditions favorable to high birth and low death 

 rates, overpopulate their native habitat, destroy their natural food sup- 

 ply and swarm out over adjacent territory. There are many reports 

 of vole and lemming plagues in Europe and Asia. In Scandinavia, 

 lemmings are said to indulge in somewhat periodic migrations from 

 the highlands to the valleys in vast droves, destroying the crops and 

 other vegetation in their paths. 10 As serious as such occasional inva- 

 sions are locally, on the whole the steady drain of normal mouse popu- 



G Fisher, Yearbook U. S. Dept. Agric. for 1908, p. 193. 



6 Bailey, Farmers' Bull., No. 335, p. 17, 1908. Dice, Journ. Mammalogy, vi, 282, 



1925- 



7 Bailey, Farmers' Bull., No. 335, 1908; N. Amer. Fauna, No. 49, p. 125, 1926. Lantz, 

 Yearbook for 1909, pp. 209-218. 



8 Bruner, Nebraska Agric. Exper. Sta., Press Bull, No. 29, 1908. 



9 Hall, An outbreak of the house mouse in Kern County, California, Univ. Cali- 

 fornia Pub. in ZooL, xxx, 189-203, 1927. 



10 Lantz, U. S. Biol. Surv. Bull. No. 31, pp. 6-7, 1907. Cabot, Labrador, 1921, quoted 

 by Allen, Jour. Mammalogy, in, 56-57, 1922. 



