10 Jul Thermal Imaging surveys for bats: practical applications
Since 2014 BSG Ecology has been using thermal imaging cameras in appropriate situations to determine the presence of bats in trees, bat boxes and other structures; and to identify flight lines and foraging behaviour to better inform the assessment of impacts on rare species of bat. We have been particularly interested in how this technique can assist us in the assessment and survey of potential tree roosts, which is always a challenging task.
Thermal imaging cameras are designed to detect heat (infrared radiation) emitted from objects within a defined field of view. The metabolic heat produced by bats and other animals produces a distinct thermal image against a cooler background. In particular circumstances it will produce a thermal plume that escapes from cavities and cracks.
The ability to detect the heat emitted from an object has several advantages as a survey technique. It is not invasive and does not require artificial illumination. It can also detect the presence and behaviour of animals over long distances, depending on the camera and lens used and the size of the animal being observed. The cameras are portable (being little different in size from a large camcorder) and are supported by software that provides image analysis and summary statistics functions.
We are using Thermal Imaging cameras to support some of our bat surveys of trees, bat boxes and buildings.
In 2014 BSG Ecology undertook a suite of ecological surveys at a site in Oxfordshire to inform an Environmental Impact Assessment prepared for a planning application for residential and employment development. As part of the concept Masterplan, a number of roads and a roundabout were proposed that would sever hedgerows and a linear block of woodland with trees with potential to be used by roosting bats. An initial assessment raised concerns about the effectiveness of normal survey methods as a number of the trees were heavily overgrown with ivy or in a condition that made tree climbing inadvisable. As a result thermal imaging was used alongside standard survey methods to provide greater confidence in the survey results.
Thermal Imaging enabled the identification of a small roost of common pipistrelle in a dense tangle of ivy stems.
This small roost of no more than three bats would have been very difficult if not impossible to locate using traditional survey methods of emergence survey, especially as the thermal imaging footage clearly showed bats crawling through the ivy and emerging at a different point to where they were roosting.
Thermal imaging can also be used to determine the use of bat boxes without the need to climb a ladder and open the box, especially when there are several bats huddled together to maintain their body temperatures at the time of survey. The image below is of a Natterer’s bat emerging from a Schwegler 1F bat box (containing a maternity roost) on a tree in an ancient woodland. Heat is clearly escaping from the edges of the door at the front of the box.
In 2015 we have used thermal imaging during internal and external surveys of buildings to identify flight paths and emergence points. In Buckinghamshire thermal imaging was used within a church to locate roosts and exit and entry points. Low level roosting activity was recorded within the church by common and soprano pipistrelles and thermal imaging footage enabled us to follow the bats flying within the knave and chancel to determine roosting locations. It also enabled us to confirm the exit point through a narrow crack in the church door.
In Devon a thermal camera was used confirm entrance and exit points used by lesser horseshoe bats through the walls of former kennels on a country estate.
Thermal Imaging is proving to be a very effective additional survey tool for situations where normal survey methods do not always provide sufficient detailed information to be confident about what bats are doing. It enables accurate counts of bats to be made and flight patterns and pathways to be identified over a range of distances. We are currently trialling the use of pairs of smaller cameras (FLIR A35) to monitor movement of bats along linear features on key commuting routes and at crossing points such as bridges or overhanging trees where new linear infrastructure (roads, railway, pipelines etc) may sever flight paths. We suspect thermal imaging will have limited uses in hibernation sites, but this again will require further trials as opportunities present themselves.
If you would like further information about our thermal imaging capabilities please contact one of our offices.
Image of Natterer’s bat emerging from a Schwegler 1F bat box used with kind permission of Dr. Tom Chapman.