THERMAL IMAGING BIRDLIFE SURVEY
13th-21st July 2021
To capture thermal images of roosting nightjars, helping to assess their nesting locations.
In the summer of 2021, we were contacted by an ecologist in Devon who was looking into the potential applications of thermal imaging drones in detecting nightjar nests. Mostly active before the break of dawn, and very well camouflaged against long grass or shrubbery, nightjars and their nests are notoriously difficult to spot without hours of field observations. After our initial contact and research into a 2021 study, upon which much of our theory was based, we identified a conducive weather window (which ended up being the ten-day July 2021 heat wave that brought about the UK’s first high temperature amber weather warning!) and embarked on a series of dawn surveys.
The theory was that we would pilot the drone in a grid-pattern transect over a number of areas that had been identified by the ecologist as locations where nightjars were known to be nesting, or where they suspected as much. Flying at a low speed and low altitude, the drone would cover the entire area, simultaneously capturing one thermal image and a corresponding RGB ‘visible light’ image every two seconds. The thermal images would then be processed using a thermal imagery analysis tool to pick out any suitably sized, anomalous heat signatures, and paired up with their corresponding RGB image to hopefully provide a clear picture of nesting nightjars.
Throughout the project, our pilot was up early and in position to conduct his first flight at 4:20am, an hour before sunrise as per the study’s methodology. Dawn was suggested as the best time for these flights as any thermal anomalies would be better contrasted against the cooler ambient surface temperature, as opposed to later in the evening when the ground would retain most of its heat from the day (particularly during such a heatwave!). And so, over the course of seven mornings, between the hours of 4:20am and 6am, we conducted 21 half-hour flights, each covering approximately 1Ha, and capturing 400-500 thermal images per flight. With the time-sensitive nature of the imagery (we would need to present any anomalies to the ecologist in time for them to be able to travel to the location and assess whether or not the anomaly was indeed a nest), our pilot would spend the afternoon running each image through thermal analysis software to identify any anomalies, or heat spikes. He recorded any anomalies that were discovered and presented them to the ecologist in the form of the thermal image, superimposed over the corresponding RGB image, orientated north, with the GPS coordinates of the centre of the image. This meant the ecologist would be able enter the coordinates into their portable GPS device, travel to those precise coordinates, face north with our orientated image in front of them either on a portable device or printed out, and know at a glance where the thermal signature was in relation to their position.
Within the thousands of images captured, 155 thermal anomalies were detected and forwarded to the ecologist: an average of 7/Ha.