54
THE ESSEX NATURALIST
urban areas (such as the Yellow-necked Mouse) have presumably
lost ground to the expanding towns. Wood Mice are most success-
ful at exploiting arable crops and the increase in arable farming
has presumably favoured them.
These changes are very minor when compared with the rest
of the terrestrial mammals. Of the species which Laver records
as being wild or feral in Essex in the 1890s three are now totally
extinct in the county (Roe Deer, Capreolus capreolus (Linn.), Pine
Marten, Martes martes (Linn.), Polecat, Mustela putorius Linn.)
and others have suffered serious declines and are verging on ex-
tinction. Since Laver's work three new species have become
established as a result of introductions (Grey Squirrel, Sciurus
carolinensis Gmelin, Muntjac, Muntiacus muntjak (Zimmermann)
and American Mink, Mustela vison Schreber), and the Coypu
(Myocaster coypus (Molina)) has come and gone again in the
intervening years. The ten small mammals, by contrast, have not
been affected by introductions: all are natives or introductions of
very long standing. All the species of small mammal found on
mainland Britain are resident in Essex and are likely to remain
so. Eight of the ten species are known to live on at least one of
the Essex Naturalists' Trust reserves. One exception is the
Yellow-necked Mouse (which occurs in the National Nature
Reserve of Hayles Wood) but it is probable that this will be dis-
covered in Shadwell Wood and the Danbury reserves when suffi-
cient trapping is carried out. The other exception is the Pygmy
Shrew but this too is likely to be present on several of the
reserves. Since the species are small, large populations can
live in fairly confined areas and even in the unlikely event of
nature reserves becoming the only suitable habitat it seems that
most species could survive! There are small mammal species
on continental Europe that could possibly be introduced suc-
cessfully. This seems unlikely to happen as chance introductions
are unlikely to become established and there is no reason for
large scale introductions to be made deliberately. It is likely
that the Essex small mammal fauna will remain less affected by
human pressure for much longer than the larger species.
Acknowledgements
We are very grateful to the many people who have contri-
buted records to this survey. Some have been acknowledged
by name in earlier mammal reports but the list is now so long
that space does not permit a personal mention of all the
helpers. Messrs M. Seear and D. R. Scott collated the records
during their terms of office as Essex Mammal Recorders. The
records from the London Natural History Society came via
Messrs J. Burton, I. Beames and M. Towns.
Many of the mammal trappings have been carried out on
private land and our thanks are due to the land-owners for per-
mission to undertake this work. Mr P. Rumsey kindly allowed