14 an ECONOMIC STUD* OF FTELD MICK. 
That a thousand of these small animal- 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-sur-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 1.850 (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 (Microtus 
arvalis) collects fallen haws, juniper berries, beech mast, acorns, and 
nuts into its burows. During the coldest weather they fall into 
uninterrupted hibernation, but when 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 winter i^ 
afforded by the economic vole (J/. oBconomus) of eastern Siberia, 
whose migrations have already been described. These animals arc- 
said to lay up large stores of food during summer — 20 and even 30 
pounds of fresh roots have been found in one hoard. 6 The Kam- 
chatkans habitually rob these stores of food for their own 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 World species. The 
habit of storing food seems to be less common in this country than 
with Old World species, but it is far from rare. Caches of food are 
often found, which show that in times of abundance the animals store 
away more than is needed for immediate use. 
One American species, the tundra vole (J/, operarius), exhibits in 
its provident habits a resemblance to the economic vole. The animal 
is small, inhabiting mossy tundras of western 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 peek or 
more in a single cavity just below the surface on a mossy knoll or 
« Tliierlebeu : Saugethiere, A. E. Brehm, vol. 2, p. P>88. 1877. 
& History of Quadrupeds, by Thomas Pennant, vol. 2, p. 194, 1793. 
