Lepus americanus
Occasionally as the mice darted into the open I made a slight squeaking noise and perhaps two or three in sight at the time would instantly turn and dash back into the sheltered road, sometimes not reappearing for a long time. Again and again I saw them come into the open for food, and before securing it suddenly scamper back in a panic without apparent cause for alarm.
Eternal vigilance is the only defense such animals have, and despite their watchfulness myriads of them are devoured daily by a large number of rapacious birds and mammals, including even such huge beasts as the great Alaskan brown and grizzly bears, which dig them from their burrows on grassy northern mountain sides.
Despite their numerous natural enemies field mice are so prolific they continue among the most destructive of agricultural pests. They are so obscure and the damage by a single mouse appears so insignificant, that it requires a knowledge of their habits, their wide distribution, and their enormous numbers to appreciate what a serious drain they are on the farmer’s income, even when in their normal numbers.
In summer they feed on growing grass, clover, alfalfa, and grain, seeds, bulbs, root crops, and garden vegetables. In fall they congregate under shocks to feed on the grain, and in winter often do enormous injury to young or even well-grown fruit and other trees by gnawing off the bark on the base of the trunk and roots, sometimes in this way destroying entire orchards and nurseries.
One species in California destroys large quantities of raisins drying in the field by carrying them off to some shelter, where they cut out the seeds and leave the rest of the fruit. I have seen half a pound of raisins under a piece of board, the result of the night’s work of a single mouse.
While field mice are always destructive, at intervals they have sudden and mysterious accelerations of increase and become so excessively abundant that they are a veritable plague. Many instances of this are on record in the Old World, where they have become so numerous as to call forth governmental intervention.
The most notable recent outbreak of this kind in the United States took place in the Humboldt Valley, Nevada, where, during the winters from 1906 to 1908, they swarmed over the cultivated parts of the valley and completely destroyed 18,000 acres of alfalfa, even devouring the roots of the plants. During this outbreak the mice in the alfalfa fields were estimated to number as high as 12,000 to the acre.
Whenever field mice become over-abundant notice appears to go out among their natural enemies, and in extraordinary numbers hawks, owls, crows, ravens, sea gulls, coyotes, foxes, bobcats, weasels, and other animals appear to prey upon them.
At no season of the year are they free from their foes, for they remain active throughout the winter, and most species apparently lay up no winter store of food. They travel to winter feeding places through series of tunnels under the snow, and it is mainly at this season that they do the most serious damage to orchards and shrubbery.