The Essex Naturalist 57
However, north of the Thames in East Anglia it is seldom recorded. The very
similar Brandt's bat (Myotis brandtii), which has still to be found in Essex, has
been recorded once in Dartford and at a few other sites in Kent, (many times at
Westerham). At the end of the 19th century there had been just two records of
the Serotine in Essex. This is a large bat, with a preference for buildings, that
emerges soon after dusk, features which, combined with its often low flight,
would make it vulnerable to Victorian collectors. That there were so few
records, suggests that this bat was indeed rare and Laver writes that the two
Essex records "appear to be the most northerly ones recorded for the species."
The present status indicates a range expansion during the last 100 years,
although contemporary changes in the countryside would appear to be reducing
the population of this bat.
The first Essex records of Leisler's bat (then Hairy-armed bat) occurred early
in the 20th century, with few reports before the present survey. It was also rarely
recorded in other south-eastern counties at this time. It is uncertain whether
this species was always present but confused with the Noctule; however it is now
more frequently recorded in Essex than in neighbouring counties. In Kent the
species is rare although a large colony of up to 164 animals was discovered in
north-west Kent in 1989 (about 12km from the Aveley roost) and one breeding
roost is known in Hertfordshire. This species is occasionally recorded in Greater
London but is rarely found in Suffolk other than during bat box surveys in
Thetford Chase. With comparable observer activity in all these areas it would
seem that Essex represents a stronghold for the Leisler's bat.
The Nathusius's Pipistrelle was first identified in Great Britain in 1969
(Stebbings, 1970), 21 records were summarised by Speakman et al. (1991), and
it has been recorded in most years since 1990. It closely resembles the Pipistrelle
and, if occurring in Laver's period, would probably have been identified as the
commoner species.
The Barbastelle was described as fairly common by Laver, yet has been rarely
recorded since. Recent records come most frequently from Norfolk where it is
found in several hibernation sites as well as a recently discovered breeding roost
in a barn. It is also occasionally found in Suffolk, where again, a potential roost
was found in a listed barn. It is possible that this woodland species is undetected
in Essex and may still be present in small numbers in suitable habitat.
Acknowledgements
I am grateful to those people who have sent in records, particularly John Cox
and Andrew Cook. In addition, bat counts at the Grays deneholes have been
facilitated by members of the Kent Underground Research Group and woodland
bunkers have been adapted by Simon Leatherdale. The distribution maps were
produced using DMAP, a mapping programme devised by Dr Alan Morton.
Finally, I would like to thank Phil Richardson, Dr David Corke and an
anonymous referee for their comments on the drafts of this paper.