I completed my first bat survey with the London Bat Group over the weekend in what was also my first experience of a roosting survey.
The site in question, Highgate Tunnels, has been surveyed 3 times a year since 2002 in order to monitor bat roosting activity. Consisting of two, 300m disused railway tunnels, the area is now specially designated for bat conservation. One of the tunnels has been sealed at each end to retain a stable air temperature and both have had bat boxes installed.
Previous site visits have identified up to 27 individual bats in these tunnels with larger number always noted in January. On the day of our survey it was a cool 4 degrees -slightly warmer in the tunnels- and so we were hopeful of a high count.
The tunnels are ideal for roosting bats. Aside from being a cool and stable temperature, the walls are full of crevices and overhangs that have resulted from decades old layers of soot and carbon which have crusted and peeled. Roosting bats can tuck into tiny gaps, often making them all but impossible to spot. As such it is important to be as thorough and methodical as possible in order to get a representative count of these cryptic mammals.
After a slow start, bat observations began to roll in, until after about an hour we had made 22 individual finds. All were of bats belonging to the genus Myotis. 16 were natterer’s, as identified by their shock white ventral fur and ears that stick forward infront of their nose, the rest were daubenton’s which typically have a darker face and coat than the natterer’s.
It is particularly important in roosting surveys such as this, that the bats are not disturbed enough to wake up. As such we only spent around 30 seconds observing each find. It also meant that we were not to use flashes on our cameras and as such I did not manage to take any good pictures.