26 AN ECONOMIC STUDY OF FIELD MICE. 



a small orchard of apple and pear trees near Washington, D, C, was 

 under observation from October to April Attacks by meadow mice 

 began in the early fall, iDossibly in August. They were continued 

 during every succeeding month, being greatest during two short 

 periods of snow. Independent of snowfall, they were greatest in mild 

 and least in cold Aveather. A few trees had no weeds or grass near 

 the trunks, and these escaped injury. The neglected condition of 

 this orchard appears from a photograph (PI. IV) taken January 24, 

 1906. Adjoining the orchard was a tangled thicket on low, moist 

 ground, in which meadow mice were abundant. 



. On March 16, 1906, I found that of 380 apple trees, 164, or over 43 

 percent, were ruined, being completely girdled, some to a height of 

 8 to 10 inches above the ground. Thirty-six others, nearly 10 per- 

 cent, were less badly injured, Avhile 180, or 47 percent, apparently, 

 were uninjured.® 



Of 200 pear trees in the orchard 50 were more or less seriously 

 damaged. The injury to these was inflicted early in the fall. 



The nature of the damage to individual trees in the orchard is 

 well shown in Plate V. 



y 



INJURY TO FOREST TRKKS. 



As an example of the danger from field mice to which planta- 

 tions of forest trees are exposed, the following is cited : In 1813 

 and 1814 young plantations of trees in Dean and New forests, Eng- 

 land, were greatly damaged by mice, probably J/, agrestis. The 

 damage was to planted acorns, tAvo-thirds of which were destroyed, 

 and to holly, oak, and chestnut trees, some of which were 5 years 

 old. Not only were the trees girdled above the surface of the 

 ground, but often the roots also were gnawed through. The land 

 was covered .with long grass, ferns, etc., which furnished abundant 

 shelter for voles.^ During the winter of 1813-14 more than 30,000 

 mice by actual count were destroyed in Dean Forest and 11,500 in 

 New Forest. It was calculated that the total killed by all the 

 agencies employed was probably double these numbers. The total 

 number of voles killed in both forests during the outbreak was esti- 

 mated at 200,000.'- 



In the past, American forestry has concerned itself chiefly with 

 efforts at conservation, but forest extension has progressed far 



a Oil .June 22. 1907, the nuniber of apple trees alive in this orchard was 22(;. 

 The (lead trees numbered 154, niaiiy of which had su(cunil)ed to their injuries 

 duriiii; the spring of 1907. The trees were thorouglily sprayed with lime-and- 

 sulphur wash in November, 1906, and although many meadow mice :uid some 

 rabbits were present, none of the trees were Mttacla'd duriiii.' tlip succeeding 

 winter. 



6 Lord Gleubervie's Account, Zool. .Journ.,- vol. I, pp. 433-444, .January, 1825, 



c Bell's History of British Quadrujwds, p. 325, 1874. 



