The Essex Naturalist
49
The Bats of Essex
John Dobson
16 Westerings, Bicknacre, Danbury, Essex CM3 4ND.
Summary
The bats of Essex have been little studied and the last comprehensive review of
Essex mammals was by Laver (1898). The results of a recent, ongoing survey are
presented with current distribution maps of all species recorded more than once
in the period 1981-1996. The Pipistrelle and Brown long-eared bat are the
commonest species as they were in Laver's time, but both Whiskered bat and
Barbastelle, apparently fairly common in Victorian Essex, were both recorded
just once during the current survey. Two migrant species, Nathusius's Pipistrelle
and Parti-coloured bat were recorded for the first time in Essex during this
period. The species showing the most marked change since Laver is the Leisler's
bat. Unknown in Essex in 1898, it has recently been recorded from seventeen
10km squares; breeding colonies have also been found.
Introduction
Bats are a declining group of mammals yet with 22 species on the British list,
(including vagrants) comprise 31% of our terrestrial mammal fauna. Recent
protection under the Wildlife and Countryside Act, 1981, has created an
opportunity to conserve both the animals and their roosting sites, but because of
the difficulties of identification, the distribution of bat species in the country has
only recently become better understood. Laver (1898) recorded eight species for
Essex, but up to 1980 there were only occasional records of bats reported to the
Essex museums or documented in reports of The Essex Field Club. This account
covers 1981-1996 and reviews those bat species recorded in Essex during the
period. Accepted records are of bats identified in the hand, by using bat detectors
(for distinctive species e.g. Noctule, Serotine) or from droppings, again where they
are distinctive. Sight records of bats made at summer roosts or hibernation sites are
also included. The distribution maps have been produced using DMAP, a software
package devised by Dr Alan Morton. The recording unit is the 5x5 km square
based on the 10 km square system of the Ordnance Survey's National Grid.
Further information can be obtained from the Essex Bat Group Annual Reports,
produced since 1984. Full details of all records can be obtained from the author.
Essex species
Whiskered bat Myotis mystacinus (Kuhl, 1819)
The only record is of an individual found in Chelmsford in October 1987. Laver
describes this bat as "more common than is generally believed" and claims to
have found it regularly in the County. In 1880, a specimen was collected from
the Grays deneholes (TQ67) but since then there have been only four records of
this species which is more often found in northern and western Britain.