Bats have a complex ecology. They make use of multiple roosting sites and types of roost throughout the year, and their requirements vary with the seasons. For example, breeding female bats usually congregate in warm, dry spaces in the summer, often in buildings or trees, to raise their young. In winter, bats usually hibernate.
For hibernation in underground structures, bats require an undisturbed site with a constant cool and high-humidity environment. Structures such as caves, mines, tunnels, bridges, church crypts and air raid shelters often provide suitable conditions for hibernating bats. Hibernation sites may also be important for more than one bat species, so it is important that they are identified if they could be affected by development or construction work.
Bats can lower their body temperature and metabolic processes to become torpid at any time of year; hibernation is an extended period of torpidity used to conserve energy during the colder months when there are far fewer flying insects to feed on. Hibernation surveys to assess whether bats are present should only be conducted, therefore, during the winter months: December to February inclusive. Disturbance also needs to be minimal during a hibernation survey because waking a bat means it consumes vital fat reserves, which can lower its chances of survival. Because of this risk, only trained personnel with a Level 2 class licence for surveying bats issued by Natural England can survey a bat hibernation site.
Inside a hibernaculum, some bat species will hang freely from walls and are quite visible, such as the Daubenton’s bat shown covered in condensed water droplets. However, others are more difficult to find and may be hiding in gaps or crevices. At RSK, our ecologists undertake systematic inspections of all apertures that could support a hibernating bat using bright torches, inspection mirrors and endoscopes. Although it can be difficult to find bats in their hibernacula, it can be even more difficult to pin them down to a species, although we always try to do this if possible.
It is possible to create ‘artificial’ hibernation sites for bats, for example, by converting derelict structures such as former World War Two pillboxes or icehouses. Existing sites can also be enhanced for hibernating bats by adding of extra roosting places such behind wooden boards or in bat bricks fixed to walls, or by measures that optimise the temperature and humidity for them. If disturbance by the public is likely, grilles and access gates can also be fitted.
We are currently conducting hibernation surveys for various clients. Please get in touch if you require advice on surveying or enhancing potential hibernation sites.
Contact: Simon Boulter, Email: firstname.lastname@example.org, Tel: +44 (0)1869 336827, Mob: +44 (0)7834 104572