Calls of the wild – the power of bioacoustics

Understanding the ecological effects of forest management processes in readiness of adaptation to climate change and the associated challenges of wildfires, novel pests and diseases is becoming critical.

I have been working with the forestry sector in the Cranborne Chase Area of Outstanding Natural Beauty, on the Dorset-Wiltshire border, which has some of the most significant tracts of ancient woodland in southern Britain. Traditionally these woods were managed using a coppice system which dates back hundreds if not thousands of years. However, coppicing has significantly declined since the 19th century as an economical way of managing our woods.

Such decline is known to have had a negative impact on some of our woodland wildlife as the woods become increasingly shaded and lacks many of the habitat niches on which many species depend. The introduction of a more viable yet novel method of irregular forestry management within these ancient woodlands provided a unique opportunity to study its effects on various woodland biodiversity.

I undertook the research for my recent PhD with Manchester Metropolitan University. The project called on my passion for recording wildlife sound ‘bioacoustics’ - which featured in my Churchill Fellowship research travels in Hungary - in helping to explain the effects of this new type of forest management on bats.

As invertebrate feeders, bats can be very sensitive to changes in the environment and are an important indicator group on the wider health of our countryside. Bats respond to changes in the structure of a woodland in terms of how dense or how open it is, and the richness of bat species and how active they are will be determined by the degree of variability in this structure.

However, bats are nocturnal which presents its own challenges in how we can best survey them. Fortunately, they are incredibly well adapted to moving around in complete darkness through using echolocation from the calls they emit and can literally see with sound. We can identify most of the species of UK bat from recordings of the sounds they produce and then inspecting the structure of the calls.

Over a summer I deployed six recording units along with a microphone capable of picking up the very high frequency calls of bats. The recorders were set out to operate remotely within three different woodland types; one managed using the novel irregular forestry, a second managed using traditional coppice management (which involves cutting the understorey on a 7-10 year cycle), and one which had not been managed at all for at least 30 years.

We used leading edge technology developed by acoustics expert Dr Stuart Newson, to check the identification of bat calls from hundreds of hours of recordings which was used in addition to me manually scrolling through more than 35,000 recordings, which took me almost three weeks! New equipment and computer applications is where bioacoustics has really come into its own in the last decade.

As a result of the research, we were able to compare how the physical structures differed between these woods and then related the bat activity between each. We found that the irregular forest management had the highest bat species richness and was important for species of conservation concern, such as the Western Barbastelle bat which is globally near-threatened. In 2021, the results were published in the Journal Forest Ecology and Management.

Dr Gary Kerr, Principal Silviculturist with the UK’s Forest Research, believes it is critical to improve the evidence base following the introduction of novel woodland management. He states that knowledge of how different ways of manipulating stands of trees affects the number and species diversity of bats (and other species) is important for the successful implementation of sustainable forest management.

Research projects, like the one we carried out, show how bioacoustics is increasingly becoming an essential part of the ecologist’s toolkit in helping our understanding of the natural world and the effects humans are having upon it. There is no doubt that the use of acoustics was invaluable in demonstrating how bats used these woodlands and this in turn is helping to inform vital woodland stewardship into the future.