28 AN ECONOMIC STUDY OF FIELD MICE. 



inches. The majority were headed low, their outer drooping branches 

 touching the ground (PL VI, fig. 1). In the spring of 1903 corn had 

 been planted by listing it in the open spaces between the rows of 

 trees; but owing to an unusually wet summer, the crop had been 

 abandoned, and sunflowers and other weeds and grasses had made a 

 luxuriant growth throughout the orchard. Over much of the area, 

 apparently, no attempt had been made to cut down the weeds; and 

 where they had been mowed they had been raked into piles and not 

 burned or removed. 



In this neglected orchard field mice — the prairie vole — had found 

 a congenial home. Already abundant in 1902, they bred plentifully 

 in the open fall of that year and in the early warm spring of 1903. 

 The ensuing moist summer also was favorable for continued repro- 

 duction, and by the fall of 1903 the}^ were present in hordes. All the 

 orchards of the neighborhood — a comparatively level upland prai- 

 rie — had been neglected and all were invaded by mice; but the one 

 above mentioned was the largest and most neglected, and therefore it 

 suffered most severely. By December 18, the date of my first visit, 

 mice had wholly or partially girdled at the surface of the ground 

 fully 5,000 apple trees and had denuded of bark many of the low 

 branches. The owners of the orchard, thinking that none of the trees 

 could survive the injuries, then estimated their loss at from $25,000 

 to $30,000. 



Examination showed that the ground everywhere was honeycombed 

 by mouse burrows and tunnels to a depth of 3 or 4 inches, and that the 

 surface was almost covered by a network of runways of the prairie 

 vole. Upon digging into the burrows at the base of apple trees I 

 found many twigs, -1 to 6 inches long, that had been entirely stripped 

 of bark and left lying in little piles. I had no difficulty in finding 

 where the twigs had been severed from low-growing branches and the 

 tips of sprouts, and in distinguishing, by the smaller tooth marks, the 

 cutting done by mice from that done by rabbits. TVhether the twigs 

 had been first stored and afterwards fed upon in cold weather I was 

 unable to determine, for I found none with bark remaining upon 

 them. Probably they Avere carried to the burrows merely for leisurely 

 but immediate consumption. 



Contrary to the usual habits of voles in our Northern States, this 

 injury had been done during mild weather. Up to December 18 the 

 season had been warm and open. Xo snow lay on the ground for 

 more than twenty-four hours. Ordinary food, such as grass, seeds, 

 and grain, was abundant, so that the only explanation for the injury 

 to trees seems to be the vast numbers of voles present and their pref- 

 erence for a partial diet of bark. 



Voles, however, were not the only animals abundant in the orchard. 

 Rabbits, both cottontails and jacks, were there in great numbers, and 



