14 AN ECONOMIC STUDY OF FIELD MICE. 



That a thousand of these small annuals often inhabit a single 

 meadow is not an extravagant estimate. Indeed, that number is 

 often exceeded. Careful estimates made in France during- 1893 placed 

 the number in one district (Bar-suf-Seine) at 10,000 per hectare (about 

 4,000 per acre). In 1904, in the Department of Charente, the average 

 number per hectare (2.47 acres) was estimated at 1,350 (540 per 

 acre). Fortunately, conditions in America appear to be less favor- 

 able to their increase, and the natural enemies of mice have not 

 yet been exterminated to such an extent that they fail to check the 

 excessive multiplication of the rodents. 



Storing Food. 



European naturalists nearly all agree in stating that field mice 

 store food for winter use and that the animals hibernate during cold 

 weather. Brehm says that the common species in Germany [Murotvs 

 arvalis) collects fallen haws, juniper berries, beech mast, acorns, and 

 nuts into its biirows. During the coldest weather thej^ fall into 

 uninterrupted hibernation, but Avhen mild weather returns they rouse 

 up and feed on their stores." Similar statements are made of other 

 species and confirmed by other writers. 



The most noted example of provident preparation for Avinter is 

 afforded by the economic vole (J/, oeconornvs) of eastern Siberia, 

 Avhose migrations have already been described. These animals are 

 said to lay up large stores of food during summer — 20 and even 30 

 pounds of fresh roots have been found in one hoard.'' The Kam- 

 chatkans habitually rob these stores of food for their oAvn use — a fact 

 which accounts for the favor with which they look upon the animal. 



American voles, so far as known, do not hibernate, but are active 

 in winter even in the far north. So thoroughly has this fact been 

 proved by observation that it seems possible that European observers 

 may be mistaken as to the hibernation of Old AVorld species. The 

 habit of storing food seems to be less common in this countrv than 

 with Old World species, but it is far from rare. Caches of food are 

 often found, Avhich show that in times of abundance the animals store 

 away more than is needed for immediate use. 



One American species, the tundra A'ole {M. operarius), exhibits in 

 its provident habits a resemblance to the economic vole. The animal 

 is small, inhabiting mossy tundras of Avestern Alaska, from Cape 

 Vancouver north to Bering Strait and up the Yukon Valley to the 

 boundary of the British possessions. According to E. W. Nelson, it 

 gathers stores of small bulbous roots, sometimes placing a peck or 

 more in a single cavity just beloAV the surface on a mossy knoll or 



a Thierlebeii : Siiusethiere. A. E. Brebm. vol. 2, p. .388. TS77. 



6 History of Qundnipeds. l>.v Tboiuas renniint, vol. 2. p. I!»4. 1793. 



