RODENTIA 249 



by mice. On one estate near Breslau 200,000 were caught in 7 weeks 

 and sold to a fertilizer factory. In 1861 the authorities paid $1,000 

 for the capture of 409,524 field mice near Alsheim, in Rhenish Hesse. 

 In 1816 and 1817 "whole districts were reduced to destitution" by these 

 mice, the department of Vendee suffering a loss of $600,000. In a 

 meadow 1000 field mice require 12 tons of grass or other vegetation 

 each year. In France it was estimated that there were from 1500 to 

 4000 to the acre. 10 In special invasions the number runs much higher. 



The first serious plague of field mice on record in the United States 

 was in 1907-1908, when Microtus montanus was estimated to have 

 reached an abundance of from 8000 to 12,000 an acre in Humboldt 

 Valley, Nevada, where the destruction of alfalfa resulted in a loss of 

 $300,000." A more serious outbreak occurred in Kern County, Cali- 

 fornia, in 1926-1927. About 15 per cent of the infestation consisted 

 of field mice (Microtus calif or nicus), the balance mostly the imported 

 house mouse (Mus muscidus). White-footed or deer mice (Peromys- 

 cus), kangaroo rats (Dipodomys) and pocket mice (Perognathus) 

 were present in only about their usual numbers. It was estimated that 

 there were 82,280 mice to the acre, and it was computed that there 

 were in one grain bin 20 feet square 3520 mice in sight at one time, 

 besides those hidden among the grain bags. Two tons of them were 

 killed in one day about one granary. Poison was placed in miles of 

 trenches, and it was estimated that there were 85,000 dead mice to the 

 mile in trenches. 12 Mice killed a sheep. "Penned in a small enclosure 

 it was unable to escape, and the mice swarmed over it, pulled it down 

 and stripped the bones of flesh/' 13 



This outbreak followed a very effective wholesale poisoning cam- 

 paign against coyotes, in which many skunks, foxes and probably other 

 enemies of the mice were destroyed. Had these predacious mammals 

 been allowed to live, they would undoubtedly have killed thousands 

 of mice during the weeks and months immediately preceding the 



10 Lantz, U. S. Biol. Sun,. Bull. No. 31, p. 12, 1907. 



11 Piper, The Nevada mouse plague of 1907-08, Farmers' Bull, No. 352, 1007 ; 

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

 1908, pp. 301-310. Bailey, Harmful and beneficial mammals of the Interior Basin, 

 with special reference to the Carson and Humboldt Valleys, Nevada, Farmers' Bull.. 

 No. 335, 1908. Taylor, Methods of determining rodent pressure on the range, Ecol- 

 ogy, xi, 523-542, 1930. 



12 Hall, An outbreak of house mice in Kern County, California, Univ. California 

 Pub. Zool, xxx, 189-203, 1927. Piper, The mouse infestation of Buena Vista Lake 

 Basin, Kern County, California, September, 1926, to February, 1927, Monthly Bull. 

 California Dept. Agric., xvn, 538-560, 1029. 



13 Humphrey, A serious plague of mice in California, Scientific American, May, 

 1927, PP. 330-33L 



