scarcity of a certain species is by no means proved by the steadfast setting of
traps which will catch with certainty, say, two or three common species. To catch
what are called the ‘ rarer’ kinds is only a matter of procuring the proper cage
and using exactly the right bait. This point most naturalists do not understand
as yet.
‘ It by no means follows,’ says Mr. Pocock,1 ‘ that a species of mammal is
scarce because it is hard to trap or rarely seen. Take, for example, the case of
our two small Voles, M icrotus agrestis and M. glareolus. A few years back it
was the custom to publish the capture of every specimen of the latter, and record
it as “ new to the county.” Yet nothing, I take it, is more certain than that
the species is, and always has been—-sit least since historic times-—abundant
everywhere throughout Great Britain. I myself have caught it night after night
in numbers in the counties of Glamorgan, Gloucester, Somerset, Devon, and
Dorset. It even outdoes Mus sylvaticus in obtrusiveness. But with the Field
Vole it is far otherwise. I have trapped it, it is true, but only at rare intervals,
and so to speak by chance; that is to say, the specimens were found in the traps,
either snapped by the hindquarters or lying in some other position, showing equally
clearly that their capture was due to pure bad luck, like an accidental dart into
the trap, and not to any eagerness after the bait. In fact, at a rough estimate I
should compute that in the case of these two species the percentage of agrestis
captured had not been higher than five; yet this is not attributable to any scarcity
on the part of agrestis, nor to trapping in unfavourable localities.^ Traps have
been set in their runs in the green -fields, and even close to the nest containing
young, but without success. Nevertheless the species is probably abundant
everywhere in meadows and hayfields, not to mention hedges and banks, where I
have myself seen it. The same may be the case with the pigmy.shrew. It may
be as abundant as S . araneus, but harder to trap. The small amount of experience
I have had of the species lends some support to this supposition, for in at least
two cases I clearly recollect that the specimens were caught in the way mentioned
above as characteristic of A . a g restis; that is to say, with their heads nowhere
near the bait. In conclusion, it may be added that in my opinion the difference
with respect to being trapped observable between agrestis and glareolus is partly,
at all events, explicable in connection with an habitual difference of diet between
the two species. At the time when I had the best opportunities of trapping
agrestis I was not aware that baits like bread, cheese, boiled potato, and the
like, which seem to be so attractive to glareolus, have no charm for the other
species.’
White varieties of this species are very rare. An albino, with pink eyes and
a slight sandy tint in the back, was taken at Chelmsford in August 1885,1 and
Mr. F . Bond records a light cream-coloured Bank Vole which was captured some
years previously in Huntingdonshire.2 Mr. Whitaker also has a cream-coloured
specimen.
The enemies of the Bank Vole are very similar to those of the Field Vole.
1 Zoologist, 1885, p. 432. 2 Ibid. 1887, p. 425.