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[Pl. 69.]][H 107.
Field Vole.
Microtus agrestis.

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In those districts where the over-zealous efforts of the gamekeeper have resulted in the partial extermination of the Weasel and the Owls, the increase of the Field Vole is so enormous and so rapid that they have at times become a plague. Crops are cleared from the fields, young trees in plantations destroyed by thousands, and even newly sown cornfields rendered unproductive by every seed being eaten. In the New Forest and the Forest of Dean great loss has been sustained at various times by their severing the roots of young trees that crossed their runs, and by their gnawing the bark of the young trunks. The most effective of the plans adopted for lessening their numbers was by sinking pits a foot and a half deep, wider at the bottom than at the mouth, into which vast numbers fell and from which they could not escape. More recently the South of Scotland suffered from a plague of "mice" that ate up everything in the fields, inflicting such serious loss to agriculture that a Government Committee was appointed to inquire into it, and it was found that the chief culprit was the Field Vole. Fortunately, when things were at their worst, a vast number of Short-eared Owls appeared upon the scene and feasted royally until there was scarcely a Vole to be found. It was found that the enormous increase in the numbers of the Voles was directly due to the warfare waged by keepers on Weasels and Owls. Matters are better, perhaps, to-day; but there are still too many keepers who destroy as vermin the very agents that keep down the real vermin. We still need a few landowners of the temper of Charles Waterton, who threatened to strangle his keeper if the latter molested a certain pair of Owls.

It was also shown at the Vole Committee of 1893, referred to above, that the Rook destroys great numbers of Field Voles—not only adults that chance to cross the fields where the Rooks are digging cockchafer grubs, but that they systematically search for the nests and eat the young.

As in the case of the Wood Mouse, there are several local races of the Field Vole that have arisen in the islands of the Orkneys and Hebrides, which have been elevated into distinct species by some recent authors. Thus, there are recognised the Hebridean Vole, the Orkney Vole, the Sanday Vole, and the Westray Vole. Mr. Barrett-Hamilton regards the true agrestis of Linnæus as not occurring in this country, where it is represented by several sub-species. The Common Field Vole described above, he says, is a distinct species, the M. hirtus of Bellamy. This, which he describes as "a newer, smaller form," he says "has replaced an older, larger M. agrestis, the latter now confined chiefly to northern regions, and with isolated southern colonies on the mountains." Seeing, however, that most modern authorities agree in retaining the Linnean name, we have considered it advisable to do so also.