Our ecologist Martin Roche took part, as a volunteer, in a bat hibernation check in Surrey, with Surrey Bat Group last weekend, with the aim of recording the number and species of hibernating bats in a mine, kiln and bunker.
During the winter, bats hibernate to conserve energy when the insect (i.e. midge, mosquito and moth) availability is low. Bats lower their body temperature and metabolic rate during hibernation, meaning they conserve energy and rely on their fat reserves. Bats need to hibernate in places that have a constant low temperature, below 5 degrees Celsius, with high humidity levels. Hibernating bats can often be found in caves, mines and cellars, but also hibernate in roof voids and barns.
The disused mine was used to extract chalk dating back to the 1880’s. The cracks and fissures in the walls and ceiling provide perfect roosting opportunities for bats. The mine has been used by hibernating Myotis and brown long-eared bats for decades, but in 1964 a greater horseshoe bat was discovered hibernating in the mine, the only record for this species within 25 miles of London. However, there have not been any records of the greater horseshoe bat in the mine since that time,
During Martin's visit, 25 bats were found in total, including, Natterer’s, Daubenton’s, whiskered and serotine. Serotines do not typically hibernate in mines and is the first record for this site!
The disused kiln was used to mine hearthstone in the 1800’s and was closed down in 1925. Throughout the kiln are numerous bat boxes installed by Surrey Bat Group, which are regularly used by summer roosting and hibernating bats. In total, 21 bats were discovered in the kiln, including, Daubenton’s, whiskered, Natterer’s and brown long-eared bats.
The disused World War Two bunker has numerous bat boxes, which are occasionally used by summer roosting and winter hibernating bats. Only three bats were found, a Natterer’s, a brown long-eared and a serotine.
Overall, the number of hibernating bats recorded during Martin's visit, show a reduction in bat numbers. Bats were also recorded to be moving within each hibernation site and between hibernation sites. This is perhaps a worrying sign, that bats are expending energy during the winter, without the availability of prey and low opportunities to replenish their fat reserves. Consistently milder winters could be the reason. With climate change, milder winters for the UK are to be expected. How this will affect our bat populations in the long-term, is yet to be seen.