Seasonal temperature and relative humidity changes are being recorded as part of research into bat swarming behaviour.
Bat lovers in the Dover area are very lucky to have an abundance
of underground workings, and volunteers from the Kent Bat
Group monitor as many of these as possible - particularly
in winter as part of the Bat Conservation Trust's National
Bat Monitoring Programme hibernation counts.
Recently, the Group has begun to realise the importance of some
of these as autumn bat swarming sites. This activity seems to be
about mating but also might have a social function, as young
non-breeding bats are often found in the swarms: 'bat festivals'
The Group has been monitoring autumn swarming bats for
four years at a Palmerston Fort which was built in the
19th Century when the fear of Napoleonic invasion was at its peak.
Last year a ringed Natterer's bat, most likely one
from the fort, was seen flying in a well in Dover Castle, within a
kilometre to the south. It is possible that the same bats were
visiting both sites. It is often considered that bats are
faithful to one swarming site, but this may not always be the
Having obtained the appropriate licences from Natural England,
members of the Group set about ringing as many bats as they could
catch in the swarming area and monitoring their activity. Gemini
Data Loggers supplied two Tinytag Plus 2 TGP-4500
data loggers to monitor temperature and
relative humidity at the castle. Recording this
information is important because bat swarming behaviour is
not well understood and it is vital to have some
idea of the environmental conditions that may trigger or delay
swarming. These robust,
waterproof data loggers are ideally suited to the
environmental conditions in the underground area of the castle, and
can be left for long periods if required to minimise the
impact of human intrusion on the site.
Similar monitoring has been carried out at the nearby fort for
some time. The data is still being analysed but suggests that
swarming takes place during the same time frame each
year, but the focus of activity sometimes varies within
the fort, possibly depending on meteorological conditions.
Temporary light tags were placed on a few Natterer's bats, in
the hope it would help determine their destination. It was intended
to analyse all the data and manual observations from both sites,
however the week planned for this operation was one of the windiest
of the season and this was not as successful as hoped, as the bat
numbers were lower than expected. The Group hopes for better
results in future years, but is now certain that the autumn
swarming activity in the area is significant; yet more research is
needed, through monitoring of these sites, for several more