Quite like dialects change from region to region, the tiny white-bellied shortwing sings a different song depending on where it is found in the dense forests of the Western Ghats in southern India. Over two centuries, the bird’s habitats have been separated by rivers and valleys, and by deforestation for setting up tea estates, and researchers have found that the birdsong is not the same everywhere.

Researcher VV Robin of the Indian Institute of Science Education and Research (IISER), Tirupati, and Chetana Purushottam of the National Institute of Advanced Studies (NIAS), Bengaluru, found in 2016 that groups of birds living in different habitats, only 100km apart in the Ghats, have developed their own birdsongs.

Thousands of kilometres away in northern India, the Ganges river dolphin is an elusive mammal that is hardly ever sighted. The dolphins, which are blind and use sound for navigation, communication and foraging, are being threatened by the development of inland waterways, a researcher has found.

Mayukh Dey, then with the National Centre for Biological Sciences (NCBS), Bengaluru, collected valuable data on the behaviour of the river dolphins in 2017.

None of these researchers used camera traps or traditional observation methods for their work. They instead relied on bioacoustics techniques — combining biology with sound.

“You just need to set up listening devices to collect sounds in the forests and then use computer algorithms to analyse these sounds. There is no human interference in this process,” says Padmanabhan Rajan, a computer engineer at the Indian Institute of Technology (IIT), Mandi, Himachal Pradesh. “Bioacoustics can be applied for a variety of uses, including population monitoring and long-term monitoring of species, and studying animal and bird behaviour using sounds.”

Bioacoustics is a cross-disciplinary research field at the intersection of physics, biology, ecology and natural history. Across the world, it has been used to describe new species, understand the genetic and cultural diversity of different species, and gain insights into the behaviour of organisms.

With the help of instruments placed on tree canopies, in the sea, on forest grounds and elsewhere, the technique is also being used to understand the ecological impacts of deforestation and landscape changes. As the research on the white-bellied shortwing showed, the felling of trees and landscape change caused by tea plantations have led to a new species.

The technique is being studied and discussed at different forums. Training sessions have been organised by experts from the Cornell lab of Ornithology, US, for specialised experts in India. One session was held in March at IISER, Tirupati, and another at the NCBS, Bengaluru, in April. But, so far, only a few researchers are applying the technique in India.

“The cost of the instruments is, at times, prohibitively expensive, and unwanted noises in the recording create difficulties in identifying species,” says Dinesh Bhatt, professor at the avian biodiversity and bioacoustics lab at Gurukula Kangri University, Haridwar, Uttarakhand.

But the benefits, clearly, are manifold. “Without being physically present or harming any animals, we are able to continuously monitor species, places and landscapes. With the help of bioacoustics, we are also able to access the relationships and associations of multiple species with each other,” Bhatt states.

While bioacoustics has been around since the 1920s, its use became popular only in the last few decades. In India, scholars have been using it to study animal behaviour since the early 2000s. Currently, researchers from the Centre for Ecological Studies, the Indian Institute of Science (IISc), Bengaluru, IISER, Tirupati and Pune, IIT-Mandi, Gurukula Kangri University, Zoological Survey of India and Wildlife Institute of India are among the few using bioacoustics in their work.

The technique led to the identification of a new species of the Himalayan thrush in Arunachal Pradesh in 2016. Swedish ornithologist Per Johan Alstrom found that Plain-backed thrush in the coniferous and mixed forest had a musical song, whereas birds found in the same region on bare rocky habitats above the treeline had a harsher, scratchier and unmusical song. This led to the identification of the new bird species.

Bioacoustics has also been used to differentiate bird subspecies in the Himalayan region. The blue-throated blue flycatcher ( Cyornis rubeculoides ) has two subspecies in the Himalayan region. One of the two subspecies was identified as a new species — the Cyornis glaucicomans — whereas another subspecies was merged with a closely related species.

“Although they did not find any major differences in the songs of these five subspecies, the vocalisation was found to be different,” Bhatt says.

Such research can help wildlife experts design conservation strategies in protected areas, says Viral Joshi, researcher at IISER, Tirupati. He adds that India is a highly biodiverse region but also among the most affected by pollution caused by human activity.

“Bioacoustics can be used as an important tool to understand rapid changes in biodiversity,” he says.

Sibi Arasu i s an independent journalist based in Bengaluru

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