- Audio recording devices can be used to answer questions in ecology and conservation, and to monitor landscapes through their soundscapes.
- Elusive species can be discovered and studied more easily if soundscapes are monitored continuously.
- Using recorders and carrying out fieldwork simultaneously may still yield the best results.
In the Valparai plateau of the Anamalai Hills, two researchers stand in a forest fragment and listen carefully. Both work on bioacoustics – studying sounds in a landscape (the soundscape) to know more about life around them.
One of them is straining to discern whether the bird that is making a sharp, cheery call is a yellow-browed bulbul or an Asian fairy-bluebird. In the dense green vegetation around them, there is little hope of seeing the bird, so she must rely on the call to identify the species.
In the meanwhile, the other researcher has just finished his own task. He has put up a small audio recorder in a Ziploc bag, and tied it to the trunk of a Cullenia tree bearing spiky ball-like fruits.
The first researcher carried out a point count of birds, where she simply stood in a spot and took note of the species around her, based mostly on their vocalisations. Data collected this way is used to explore the species diversity in forests and estimate the abundance of birds at small scales. Studies like this are reliant on a high level of expertise, on-the-ground effort and time. Often, such surveys are carried out early in the morning, and nocturnal birds and birds of prey are overlooked.
The second researcher, who placed recorders in the field will enjoy several advantages over the first one’s method. Huge swathes of forests can be covered by placing multiple units simultaneously, and recorders can be programmed to collect data throughout the day, for weeks at a time. This data, free from individual bias, can be reanalysed many times over to answer a variety of questions. If programmed to capture sounds of the appropriate frequency, these recorders can capture bat, frog and insect vocalisations in addition to bird calls.
Click to hear the bird calls. Audio recordings of a habitat can be used to identify species diversity, estimate the abundance of birds at small scales and much more. Graphic by Kartik Chandramouli.
V V Robin, an assistant professor at the Indian Institute of Science Education and Research, Tirupati, has been using bioacoustics to answer questions in ecology.
“The advantage of bioacoustics and using recorders are immense. One of the most popular usages of technology is the implementation of cameratraps to count tigers at a nationwide scale. However, one can imagine that sound travels farther (in most wooded landscapes), and one could potentially cover a larger area with acoustic recorders. Detecting rare species is one important application that acoustic tools can be used for. Another conservation application is understanding the impacts of humans on biodiversity,” he said.
Using recorders to detect elusive species
Robin’s student, Chiti Arvind, is currently working on detecting a critically endangered bird, the Jerdon’s courser, in the Sri Lankamaleswara Wildlife Sanctuary in Andhra Pradesh. In these scrub forests, Arvind placed recorders and programmed them to record sounds from dusk to dawn, in an attempt to capture the call of the elusive nocturnal bird.
“We are now creating a template of the Jerdon’s courser call from previous recordings collected by Dr. P. Jeganathan (the only known recording of this bird). This will then be used to screen the recordings retrieved from our acoustic recording units to find a similar vocalisation match using available song analysis softwares,” she explained.
A few years ago, trying to rediscover a bird like this would have meant setting out camera traps or laboriously looking for footprints of the bird in sand. “Though these methods initially helped in the detection of the Jerdon’s courser, their success rate was not very high. Since this bird is nocturnal and cryptic, bioacoustics is a good technique to implement, considering previous successful studies on similar birds. Using automated recorders, we can also monitor larger areas with the least human interference. Our aim is to create a detection framework for the long-term monitoring of this bird using bioacoustics,” signed off Arvind.
Monitoring landscapes through soundscapes
Besides looking for enigmatic species, monitoring bioacoustics in forests can also inform conservation. Researchers often look at recordings as ‘soundscapes’ – the collection of all sounds in a given landscape.
Setting up recorders in understudied tropical forests can provide the first baseline information on the biodiversity within. A saturated soundscape is considered a sign of a healthy ecosystem, and sudden changes may point to anthropogenic disturbances from logging and hunting.
Climate change may bring about more gradual changes. All over the world, researchers have documented phenological changes due to a warming planet, where birds and frogs call for mates earlier in the season. Bioacoustic monitoring of forests can help make the link between rising temperatures and changes in the behavioural ecology of animals clearer.
In disturbed forests, invasive species that have taken over the landscape sometimes mask the vocalisations of endemics, and recordings from these forests could offer the first indication of such takeovers.
Analysing soundscapes from an area over time, helps researchers know more about the biodiversity and the health of the habitat.
Read more: [Commentary]: What sounds can reveal, if we listen
Combining bioacoustics with fieldwork
While recorders offer some definitive advantages over doing fieldwork, data collected from recorders can quickly add up, making storage and management a nightmare. Besides, experts need to provide training data before algorithms can be used to recognise and match patterns. Unless a renewable source of energy can power recorders, studies that rely on continuous monitoring will burn through an astounding number of batteries.
Viral Joshi, another student in Robin’s lab, has been an avid birder for most of his life. Over the past few years, he’s also dipped his toe in bioacoustics analysis. He believes that the best approach is still one that combines on-the-ground surveys and recording devices.
“I now use my knowledge of bird calls to understand complex behaviour using advanced analysis techniques and tools,” he said.
Soundscapes, like landscapes, are indicative of regional diversity, and can be thought of as an important regional marker. These often change along a gradient of human activity, with anthropogenic noise replacing natural sounds in cities and towns. There is a strong case to preserve natural soundscapes – preserving them is tantamount to preserving the diversity of our wild places.
Robin is hopeful about the future of bioacoustics in India. “I think there is a lot of potential for this field. It is at the interface of ecology, physics, neurobiology and behaviour. Its applications can be very wide, and can even be used in critical aspects like town planning, and inform policy.”
CITATION:
Burivalova, Z., Game, E. T., & Butler, R. A. (2019). The sound of a tropical forest. Science, 363(6422), 28-29.
Burivalova, Z., Towsey, M., Boucher, T., Truskinger, A., Apelis, C., Roe, P., & Game, E. T. (2018). Using soundscapes to detect variable degrees of human influence on tropical forests in Papua New Guinea. Conservation Biology, 32(1), 205-215.
Pijanowski, B. C., Farina, A., Gage, S. H., Dumyahn, S. L., & Krause, B. L. (2011). What is soundscape ecology? An introduction and overview of an emerging new science. Landscape Ecology, 26(9), 1213-1232.
Banner image: Asian fairy-bluebird. Photo by Rahul Alvares/Flickr.
