Bat call library for the western Himalayas takes wing

Water pipes hugging a building, hostel dorms, intersections of cedar forest and scrub-covered hills, edges of an oak forest in a village, and open streams. The maiden systematic survey of bats through disparate sites in a rapidly urbanising Uttarakhand has seeded the first bat call library from the western Himalayas for research, monitoring, and conservation.

“In total, we captured and examined 35 species of bats during our survey and recorded the echolocation calls of 32 of them. Calls of nine of them were recorded for the first time in the world,” said Indian chiropterologist Rohit Chakravarty who led the effort in collaboration with Nature Science Initiative (Dehradun), Indian Institute of Science (Bengaluru), and Natural History Museum of Geneva.

The survey unveiled a new species record for the Indian subcontinent and eight for the western Himalayan region spanning Himachal Pradesh, Uttarakhand, Jammu, and Kashmir. Also, the survey updates the checklist of bats for Uttarakhand to 49 species by reviewing previous literature. “We also genetically characterised 26 individuals of 13 species using the cytochrome oxidase-I gene to produce reference DNA barcodes of bats,” noted Chakravarty. The genetic data are used to identify or “barcode” that organism to distinguish them from other species.

In India, a clutch of chiropterologists, including Chakravarty, has set the ball rolling to create acoustic databases – a daunting task given the country’s bat diversity. India has a vast diversity of bats with at least 128 species of bats belonging to nine families.

Uttam Saikia of Zoological Survey of India, who had earlier inventoried bats in Himachal Pradesh, commended Chakravarty’s work to catalog and update bats diversity in the region and build up a call database. “It is a significant task to build reference call databases because our country has a rich diversity of bats. Many of the bat species in India need urgent conservation action in view of continued destruction and degradation of habitats. Unfortunately, bats are not legally protected in India, except for two species,” said Saikia.

“It is crucial to monitor the different species. In the western Himalayas, we also need to inventory bats in the Jammu and Kashmir region where there is a serious data gap,” Saikia, who was not associated with the Uttarakhand survey, told Mongabay-India.

In 2020, Saikia and collaborators, documenting bat diversity in Meghalaya, the Indian state that harbours half of the country’s recorded bat species, provided the echolocation call data of three species from the northeastern state.

Saikia goes on to reiterate that “despite limitations of echolocation call data, if you know the call characters, then just with the help of a bat call recorder, you can have a good idea of the species present in an area.” “However, it doesn’t give you an idea about the abundance of each species as individual calls can’t be distinguished through the detector,” said Saikia. 

“But encounter rates of species can also help in giving reasonable estimates of relative abundance or rank species based on their commonness/rarity,” adds Chakravarty.

Certain species have similar calls, so you can’t tell those species apart, said Chakravarty. “But the calls give you data about where the bats are flying, where they are feeding, and what kind of habitats they prefer over another, and in the case of Uttarakhand, their elevational distribution.”

Researchers who developed the “first nation‐wide library” of bat echolocation calls for Mexico, a megadiverse country, said in a recent paper that acoustic bat libraries can lend a helping hand to “address a range of ecological questions including the effects of human-caused activities on bat communities through the analysis of bat sound.”

“Bioacoustics is becoming more and more affordable. Just as camera traps are used to estimate the tiger population, it is not hard to put out bat detectors that work as a camera trap in the context of bats. You can put out bat detectors, and they can record bat activity night after night. You can train forest guards to do it,” explained Chakravarty, who is with the Department of Evolutionary Ecology, Leibniz Insitute for Zoo and Wildlife Research, Berlin, Germany.

“For example, I have only caught the European free-tailed bat (Tadarida teniotis) once but recorded it everywhere. Because we have their call record, we can tell they are everywhere in Uttarakhand.” The European free-tailed bat is one of the eight species that are new records for the western Himalayas.

Chakravarty studied 22 sites in the state’s Garhwal division for two summers (2016 and 2017) covering an altitude from 600 metres to 3000 metres above sea level. 

He adds: “If you go on with the exercise of recording bat calls in different locations and continue for the long term you can build a database that is not only useful for understanding bats and their natural history but also for understanding the impacts of climate change.”

Bats can signal environmental stress. Chiropterologist Merlin Tuttle writes on his website that mass die-offs of bats and other animals are early warnings of serious environmental stress. “They form the largest, most vulnerable aggregations of any mammal except Homo sapiens, have similarly wide distribution, complex biotic and abiotic requirements, and traditional ecosystem dominance. Many are exceptionally long-lived and occupy high trophic levels.” Experts have also stressed on looking at the combined effect of climate change and habitat loss.

Chakravarty adds that bats are sensitive to environmental fluctuations because they depend on insects that are quick to respond to environmental perturbations.

Uttarakhand is on the frontlines of climate change. An Indian government report highlights that the Hindu Kush Himalayas (HKH) have experienced a temperature rise of about 1.3 degrees Celsius during 1951–2014. And it is projected to warm up more.

The appeal of Uttarakhand for bat survey

Systematically cataloguing bats and creating a baseline dataset for Uttarakhand makes a lot of sense — the habitat diversity along the Himalayan gradient, biogeographical positioning, and an enigma that goes back to bat surveys of the British colonial period.

“Formal surveys of bats were done in the 1870s during the British colonial time. Cities such as Mussoorie have changed quite drastically,” pointed out Chakravarty.

Some regions in Uttarakhand were re-surveyed in the 1960s and 1970s and again in the 1990s in which Eonycteris spelaea and Sphaerias blanfordi were recorded for the first time from western Himalaya. In 2004− 2006, comprehensive bat surveys were conducted in Himachal Pradesh and Nepal.

Uttarakhand is also at a vantage point in terms of biogeography – Uttarakhand “sits at a point where assemblages of species Europe, the Far East, and peninsular India meet.”

It is also home to one of India’s rarest bats, Peter’s tube-nosed bat (Harpiola grisea), which was last seen in Uttarakhand’s Mussoorie region in 1872. “And for 150 years that was the only known location of that species; since the 1870s nobody has seen that species in Uttarakhand. It was found in Mizoram in northeast India all the way across but we still don’t know what is the status of the mystery bat in Uttarakhand. I didn’t find it,” added Chakravarty.

Aided by field assistants, Chakravarty worked his way through a mix of sites through the state – quaint Garhwali villages, areas around protected areas such as Kedarnath Wildlife Sanctuary, rivers that flow into Dehradun, forest pockets in Mussoorie range-reflecting the diversity of habitats spaced out along the Himalayan gradient.

Most of the areas surveyed – through sal-shrouded foothills to rugged oak, pine, chir, and rhododendron covered forests higher up in Uttarakhand – were outside protected areas.

“From my experience bat distribution appears to be patchy in Mussoorie. Wherever there are valleys with good forests, there are a lot of species. All the species are in that island of greenery. If I compare my capture from Kedarnath and Mussoorie, I actually catch fewer bats in Kedarnath with the same amount of effort. But I don’t have a measure of their activity. In the Mussoorie range, these small pockets of forests have many bats species and a lot of activity and in Kedarnath, the bats are more spread out,” said Chakravarty.

The highest number of bat species was recorded in Devalsari (10 species), at the intersection of scrub-covered hills and cedar forest, and in the 1,000–2,000 m elevational range (20 species).

One female of the rare sombre bat was caught at the edge of a subalpine rhododendron forest at Shokharakh in Chamoli district. Five individuals of the long-tailed whiskered bat were caught in Devalsari in Tehri Garhwal district and primary oak forest, and forest edge in Mandal in Chamoli district. The long-tailed whiskered bat is a new record for the entire Indian subcontinent, the study said.

Two individuals of the hairy-faced bat (Myotis cf. annectans) were caught at Devalsari and one in Mandal at the edge of an oak forest. One Joffre’s pipistrelle (Mirostrellus joffrei) individual was caught flying over an open stream at the edge of an oak forest in Mandal village.

At Taapu Sera close to Dehradun city, nets set up by Chakravarty and his field assistant at a spot surrounded by steep slopes caught 30 individuals of the European free-tailed bat- a species that had only been reported from three other locations in India till that time. A roost of around 15 individuals of European free-tailed bats was also found behind three vertical water pipelines in the Forest Research Institute’s main building, in Dehradun.

“From my observation European free-tailed bat is a generalist species; in Kedarnath, we recorded this bat everywhere from the foothills to 3500 metres,” said Chakravarty.

Reference sequences in poorly sampled areas

But just baseline data isn’t enough to draw parallels between urbanisation and bat populations and diversity. “We can’t claim too much on the natural history of these bats from the data because we have only caught them and catching bats also has its own biases. You put up a net in a place where you can catch bats, which’s the first bias. If you simultaneously use bat detectors to find out more about their activity, that’s a relatively more unbiased way of understanding the natural history of bats,” said Chakravarty.

As a signatory to the Convention on Biodiversity, all states in India must document their diversity. In this regard, the Uttarakhand survey fills a crucial gap in the state, and the checklist presented here will find usefulness in species management and conservation, the researchers add.

It was a choice not to keep vouchers (preserved specimens) from the captured bats and to try to identify species based on photographs, external measurements, echolocation calls, and for some individuals, on non-lethal genetic data, said Chakravarty. But for poorly studied areas such as Uttarakhand, reliable identification of several taxa, including some extremely rare or potential new species, was not feasible without additional craniodental investigations.

For example, pipistrelles that are most common around our neighbourhood are the trickiest to identify. Also, several taxa are still poorly known or absent from India’s available identification keys, Chakravarty adds.

“I have run into a situation where I possibly have new species but I can’t describe them because I don’t have specimens. I collected blood samples and sequenced their DNA. The problem is you don’t know what to match it to. These species have never been sequenced; you can claim photographically that this is that species, but with bats, the differences are very minute. You have to take precise measurements, and you have to look within their bodies, and that’s why you have to catch them,” he elaborated.

The researchers “strongly recommend that bat surveys conducted in such species-rich but poorly documented areas as the Himalaya should include a reasonable collection of voucher specimens. These specimens must be deposited in public repositories such as those of the ZSI, to be accessed and properly identified by specialised taxonomists.”

“In saying this, we, of course, do not advocate the indiscriminate collection of specimens but highlight the need for better reference sequences in poorly sampled areas. The ultimate goal of taking vouchers must be to create unequivocal non-invasive identification of the species so that future researchers do not have to kill individuals of the same species for their research.”

Banner image: As many as 15 individuals of European free-tailed bats were also found behind three vertical water pipelines in the Forest Research Institute’s main building, Dehradun. Photo by Rohit Chakravarty.