THE COMMON FIELD VOLE 
conditions have caused their numbers to increase beyond normal bounds, 
and what is known as a ' Vole plague ' or a ' Vole year ' occurs. 
In such circumstances the animals swarm in masses over agricultural 
lands like a scourge of locusts, eating every green blade and barking the 
stems of young trees. 
On these occasions, it has usually been noticed how speedily this 
concentration of animal life attracts the attention of various birds and beasts 
of prey, such as Owls, Kestrels, Weasels, and Foxes, who decimate the 
hordes, but hardly account for the sudden disappearance of the plague, 
which generally happens from natural causes. These are chiefly the failure 
of the food supply when the fields are eaten bare, and consequent weakness 
and disease. 
In Great Britain 'Vole years' are comparatively rare, but from 1891 
to 1893 a great increase of the species occurred in the border lands of 
Scotland, where many miles of grassland were devastated. 
A succession of mild winters seems to be a contributory cause in the 
abnormal increase of this species, while hard winters with severe frosts help 
to keep their numbers within bounds. 
The Field Vole breeds three or four times in the season, producing 
from two or three to nine young at a time. 
The nest is made of grasses and placed either on the surface or in a hole 
underground, the situation depending on the time of year. Mr. Millais 
observed a pair making their nursery and was struck with the rapidity with 
which they carried out the work. 
In the part of Surrey with which I am best acquainted, I find the Field 
Vole — sometimes called the ' Old Sheep-dog Mouse ' from its short tail — 
to be generally less abundant than the Bank Vole, whose numbers seem less 
liable to fluctuation, and, owing to the almost exclusively vegetarian tastes of 
the former, it is seldom tempted by the ordinary bait in mousetraps. 
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