Interview

Bats are highly sensorial creatures and like birds, they orient to Earth’s magnetic fields. Seen here is an Arielulus circumdatus. Photo by Rohit Chakravarty.

 

Pitch Perfect: Foraging Calls, Mating Songs, and Other Bat Escapades

By Susan Mathews, in an interview with Rohit Chakravarty, a bat researcher working in different landscapes in India, and founder of a bat call library.

They billow from a hillside in Cha’am.
Together, they are more than plural:
the planet’s darkest song, a tongue,
a serpent muscling air apart,
a dire banner come unfurled,
a river flowing wholly from
the old, mute mountain’s desperate heart,
the last confession of the world.
Conceive of each one singly, if you can.

— Bats, Luke Hathaway

There are few creatures as reviled as our mammalian kin, bats. Mistreated, maligned, and misunderstood, whether it be in folklore or popular culture, they really have got the short end of our human stick and the worst of our primate imagination.

Far removed from our distorted associations with vampires or winged devils and our fear of anything nocturnal, Rohit Chakravarty mentions in our interview how gentle bats are, and how carefully they must be handled when caught for research, so they aren’t accidentally killed. And the one thing that really struck me from my interview, is as Rohit puts it, “They’re super-animals! They fly, they echolocate, they can become inactive when the environmental conditions are not right.” A powerful lesson in resilience.

Bats have been around for a long time, and fossil records indicate that they appeared in the Eocene 50-55 million years ago and belong to the order Chiroptera (meaning hand-wing). Based on morphology and behaviour, they are divided into two suborders—Microchiroptera and Megachiroptera—but advances in molecular biology have revised this classification to ‘Yangochiroptera’ and ‘Yinpterochiroptera’. Worldwide, there are over 1,400 species of bats, and they make up roughly 20 percent of the world’s extant mammals. “In India, bats constitute the most diverse mammalian order,” currently at 135 species.

As Rohit writes in this article, “Bats play an important role in a variety of ecosystem services like pollination, seed dispersal and insect pest control. In addition, bats are important biological indicators on account of their high species diversity, sensitivity to environmental changes, higher trophic position (of insectivorous bats), long life span, and slow reproductive rate.”

A Library of Visual Sound

Bats are highly sensorial creatures and like birds, they orient to Earth’s magnetic fields. Commentators have noted that they may not depend on one device alone to navigate but combine several in a sensory collage. Echolocation plays a central role here for microbats who ‘hear’ to ‘see’.

Bats also vocalise, and in this essay, one of the things I wanted to know more about was bat calls and songs: how they are recorded, what they tell us. And I couldn’t think of a better person than Rohit for this, given that he has started a bat call library in Uttarakhand in the Himalayas, a project hosted by the Nature Science Initiative.

A bat call library is a common platform and source of bat reference calls for analysis and research. Rohit’s personal bat call library, hosted on his blog, now stands at 60 species, which includes common species such as the Indian Pygmy Bat to rare, range-restricted species such as the Sombre Bat. In the future, he hopes to have a common platform on which bat researchers across South Asia can collectively host their recordings. (Global databases such as Chirovox and Xeno-Canto now exist for this purpose.)

Rohit Chakravarty is a bat researcher with experience of working in different landscapes in India, predominantly the Himalayas of Uttarakhand, and Andaman Islands. Photo by Kaushal Patel.

The bat library begun by Rohit and team is one of the largest echolocation call libraries by species and the largest among the few published in India. As Rohit notes in this article, “Our study sets up a crucial baseline on diversity, local and elevational distribution, and echolocation calls of the bats of Uttarakhand. As a signatory to the Convention on Biodiversity, this allows for state reporting on India’s diversity and filling crucial gaps in Uttarakhand in terms of species management and conservation. Given that Uttarakhand lies in the junction of the Palaearctic and Indomalayan zones, this call library is of importance to ecologists, taxonomists and biogeographers.”

So, what do bats sound like? Being nature’s sopranos, bat calls are mostly pitched at too high a frequency for human ears, so they can only be heard or recorded using a bat detector, an ultrasonic voice recorder. Individual bat species emit calls with specific characteristics related to their size, flight behaviour, environment, and prey types.

This means that with the aid of bat detectors, we can identify many species by listening to their calls or recording them for sound analysis on a computer. This is through using spectrograms (a time-frequency (X-Y) graph). So, some bats see by hearing, and we hear by seeing, they hang upside down, we hang down-side up and it all makes perfect sense.

Using bat detectors reduces the need to catch bats, and they are a cost-effective way to collect data on bat diversity activity and outreach. As Rohit notes in our interview, “If the only way to ‘see’ bats was to catch and watch them, then bat watching would have never been accessible to the public. Bat detectors allow people to ‘see’ bats from a respectable distance, understand the species in their surroundings and so on. Bat watching using bat detectors is indeed a popular recreation in Europe and the US. Now it’s time to bring it to India.”

So, some bats see by hearing, and we hear by seeing, they hang upside down, we hang down-side up and it all makes perfect sense.

Apart from bat detectors, a typical toolkit for Rohit includes mist nets (thin nylon nets that are installed like a badminton net on two poles), vernier callipers, spring balance to measure the body of the bat, and gloves for handling bats and protecting your fingers from their bites.

Rohit’s toolkit. This includes field guides, headlamps and flashlights, bat detectors, camera, GPS, vernier calipers and spring balance to measure bats, nets to catch bats and, of course, gloves to keep oneself protected from bitey bats.

Decoding bat calls, and citizen science

Bat calls, according to Rohit’s blog (Bat Call Identification 101), include calls recorded when releasing a bat, free flying calls, feeding buzz when they are going in for the hunt, social and distress calls. Release calls provide the best means of identification of species while others provide researchers with varying degrees of confidence both in terms of identification as well as information on what the bat is up to. For social calls, some are audible to those without hearing impairments and others can be made audible for their melodious properties by down-sampling.

In our interview Rohit describes, “The bulk of the calls that we record from flying bats are calls that are used for navigation and finding food (‘echolocation calls’). These are simple calls designed specifically for the purpose of returning simple echoes that the bat can analyse in a couple of milliseconds to decode all the information. The information can be any of the following: ‘Stop! Turn around! Predator ahead!’, ‘Chase! Crunchy insects ahead!’, ‘Caution! Roadblock!’, ‘Slight detour! Your buddy, is chasing an insect!’.

Apart from echolocation calls, bats use a whole bunch of complex vocalisations that are either emitted in flight or while at a perch. And because we can’t observe the caller, or its gender, we don’t fully understand these calls. For most Indian species, we don’t know which calls are used for mating, defending territories, calling to a friend, etc. Therefore, scientists are forced to lump these calls into a broad category called ‘social calls’.”

Joffre’s Pipistrelle (Mirostrellus joffrei)—a species that is known only from a few locations in India. For three successive years in Uttarakhand, the team had great captures of this species, including pregnant females. Photo by Rohit Chakravarty.

Rohit with his bat detector. Bat detectors allow people to ‘see’ bats from a respectable distance, and understand the species in their surroundings. Photo by Rajesh Puttaswamaiah.

Some bats remarkably also sing, and can even sound “uncannily, spookily, like songbirds, with the trilling, the chirping, as if they were nightingales.” Their songs are complex, with multiple syllables, phrases, repeated patterns, and rhythms, only rivalled by whale songs.

Singing fulfils a social acoustic function, and it has not been well studied in bats. Songs are longer than calls, which are like pulses, pings or clicks, and songs are generally related to courtship and territorial behaviours. So, think of Bocelli or Pavarotti if they were bats looking for a mate or singing some territorial songs as ‘acoustic beacons’, in turn arousing some phonotaxis (the movement of an organism in relation to a sound source) in the females.

Fascinatingly, there is so much more to learn, including the anatomy of bat vocalisations. A new study in the prestigious journal PLOS Biology reports that for some sounds, bats use the same technique as human death metal singers and throat singing members of the Tuva people in Siberia and Mongolia to expand their vocal range. And the team has for the first time filmed what goes on in a bat’s larynx when it produces sounds. Physical structures within the larynx oscillate to make different vocalisations. For example, low frequency calls using ‘false vocal folds’— like human death metal singers. Together, the normal vocal range for a bat spans seven octaves, surpassing what a few singers like Mariah Carey, Prince, and Axl Rose can reach, which is a range of 4-5.

I really could go on about bats and their arcane feats, but in this piece, I wanted to focus on their extraordinary vocal feats and the amazing work being done to record bat calls in India. But there are so many wonderful things about them, some more that you will glean in the rest of the interview excerpts with Rohit, and others I must mention in passing.

For example, poet, essayist, and naturalist Diane Ackerman writes in In Praise of Bats of bat emergence—when they exit en masse, let’s say, from a bat cave, or re-enter it. Comparing it to a living volcano, she refers to it as one of the most spectacular sights of nature: “There was no way to hear individual voices in the ultrasonic mayhem of the emergence.” Conceive of each singly if you can.

When I asked Rohit how he sees the future of the bat library, he informed us, “How I envision this library going forward is in enabling citizen science. Imagine, if we could catalogue more calls from across the country, we could simply hand over bat detectors to citizens in different cities, ask them to follow a standard protocol, and record bats in different habitats. Initially, this data will have the potential to feed into town planning. However, over a period of 20 years or so, this will help assess fluctuations in bat populations, whether ranges expand or contract due to climate change, and we will finally have such long-term datasets for the Global South, where now we lag behind the Global North.”

Read the following edited (and often very funny) excerpts from my interview with Rohit, on his fabulous forays into the world of bats, and adventures along the way.

You recently completed your PhD. How would you describe your PhD to us, as bat novices?

My PhD was all about hiking and catching bats in the Himalayas in the Indian summer and sulking through Germany’s (where I did my PhD) grey winters. In my PhD, I studied how bats avoid competition among themselves in regions of high vs low diversity. Too technical, right? I’ll simplify.

Recollect your high school or college days when you were in a hostel sharing a room/flat with one or many people. You’d naturally use certain tricks to avoid overlapping your schedule with your room/flatmates. For example, not storing your favourite chocolate in the common fridge, but hiding it in your wardrobe. Sleeping early or with your earplugs on to avoid the loud moaning sounds of your flatmate’s sex partner. Changing your daily pattern from diurnal to nocturnal to get some work done and so on. The more the flatmates, the more the chaos.

Now take this scenario to bats living in a mountain range. In the low elevation, you have many more species. The high elevations are challenging environments with fewer species. How do different species of bats avoid competing? That’s what I studied, and in one sentence what I found was: bats in the lower elevation don’t really compete much. There is probably enough food for everyone. In the high elevations, certain bat species eat specific things that are different from other bats to avoid competition.

Give us a description of how you came to work on bats, and your earliest memories. How has it shaped you as a person?

Growing up in Nagpur, I fell in love with wildlife in the most stereotypical Nagpuri way—by seeing a tiger. Very soon I realised that the tiger is a boring animal which doesn’t move much. There are other active and fidgety animals more worthy of my attention. I was always inclined towards small mammals like mongooses, civets, bats. But watching them was hard because some of them are nocturnal. Thankfully, the opportunity came to us.

My brother (also a wildlife enthusiast and a wildlife cartoonist) and I rescued a bat in Nagpur which had got entangled in a manja (nylon kite-flying thread). That was my first experience of holding a bat and realising how vulnerable and innocent the animal truly is. That same year, two more bats found their way to our house. However, the deal wasn’t sealed until I moved to Mumbai for my bachelor’s degree and started exploring caves with my college friends. This completely changed my life, and from there on, I stuck to bats.

Studying bats has taken me to some of the most exciting habitats/ecosystems like islands, mountains, and caves. Also, the forests that people walk during the day, I get to walk at night and it’s a totally different experience!

As a person, I feel that bats have made me realise the benefits of choosing a less-trodden path. There are so few people who study bats in India that anything I, or other bat researchers do, turns out to be new.

Rohit with his field assistant Zareef Khan, preparing to set a mistnet along a stream in Uttarakhand. Water bodies bring bats down to ground level, both for insects and for water. Setting nets along such areas allows us to get good captures of bats that can then be identified at hand and recorded. Photo by Farah Ishtiaq.

Rohit’s team at play while waiting for the sun to set and for bats to emerge from their roosts. Photo by Taksh Sangwan.

What do you love most about working on bats?

What I love the most is the experience of embracing the unknown. We don’t know much about them and when I do fieldwork, I go out without any expectations. Everything we find turns out to be interesting.

I particularly remember the time when we caught our first Bronze Sprite. It’s a beautiful bat with coppery-red fur that is tipped with black. We had simply put a net up in a brook at the edge of a high-elevation (3000 m) rhododendron forest. We had no idea that this bat lived in that habitat, or even occurred in Uttarakhand; our capture was the first time it had been caught in Uttarakhand. When the bat got caught, the entire field team—two local field assistants and I—were overjoyed. They joked that it looks like the bat has applied henna (alluding to its red fur).

Studying bats has taken me to some of the most exciting habitats/ecosystems like islands, mountains, and caves. Also, the forests that people walk during the day, I get to walk at night and it’s a totally different experience!

Tell us about a bat memory that really stood out?

In the Andamans, I was assisted by Saw Isaac who belonged to the Karen community (a group of settlers from southern Myanmar). He was a dead ringer for Jackie Chan. We were catching bats in Interview Island, which is uninhabited with only a reserve police force. In a cave there, we caught a nectar-feeding bat called the Dawn Bat (Eonycteris spelaea). The males of this species have enormous testicles (many bats do!). I was examining a male when Isaac asked me the name of the species. I said, “Dawn Bat.”

Isaac, who did not speak English, gave a detailed look at the testicles of the male bat and exclaimed (in Andamanese Hindi), “It is truly a Don.” After that, I found it pointless to explain the meaning of Dawn because Don indeed seemed more apt.

Which are your favourite books on bats?

I’d only like to list one, which is part scholarly and part popular. It’s an old 1960s book called Silently By Night by Russell Peterson. My aunt, who is also a wildlife enthusiast and an avid reader, found this book in her father’s library who had, in turn, picked it up from an antique bookstore. After I started taking interest in bats, she gifted that book to me. And boy! What a fine read it was! A rare one too. It’s one of the finest pieces of accessible scientific writing, written with genuine love, respect, and passion for bats.

In relation to bats, which is the one place you keep returning to?

There are a few—some that I still visit, others that are now inaccessible but still fresh in my memory.

The first is a cave around 30 kilometres from Nagpur visited often by my brother and I, hosting a colony of Fulvous Leaf-nosed Bats (Hipposideros fulvus). But more than the bats, every time we peeped into the cave, we saw something new: a pair of porcupines, and once a Jungle Cat!

The second is Feroz Shah Kotla in New Delhi. Ever since my friend Rajlakshmi Mishra—a researcher who studied Delhi’s bats for her PhD—introduced me to this place in 2015, I have been there on most visits to Delhi. It has a lovely dungeon replete with Mouse-tailed Bats. Unfortunately, the last time I went there in 2023, the dungeon was sealed off for the public.

The third is Golconda Fort in Hyderabad. It houses a massive colony of some 20,000 Fulvous Fruit Bats (Rousettus leschenaultii), possibly the largest urban bat colony in India.

And lastly, Kedarnath Wildlife Sanctuary in Uttarakhand. My last visit here was in 2021, during the last season of fieldwork for my PhD. This place houses my favourite sites for trapping rare and enigmatic species of bats like the Joffre’s Pipistrelle (Mirostrellus joffrei), Little Tube-nosed Bat (Murina aurata), and Bronze Sprite (Arielulus circumdatus).

Rohit removing a Woolly Horseshoe Bat (Rhinolophus perniger) from a net. Photo by Emily Stanford.

Given how bats are often reviled and maligned, this threatens their conservation. With the Nipah virus and fears of disease, how do we counter such views of these animals as just purveyors of disease?

When COVID-19 hit, a colleague, Baheerathan Murugavel, and I brought together 64 bat researchers from all over South Asia to do a press release. In it, we explained why bats should not be maligned, why killing bats is going to be counterproductive, and how we must co-exist with them. This press release was picked up in over 10 regional languages, in both print and electronic media. Additionally, most of us also did webinars and bat walks to further eradicate myths and propagate ‘positive vibes’ (sorry, just trying to adapt to Gen Z lingo) about bats.

So, to circle back to your question, the biggest problem that bats face all over the world is their bad PR. But that problem also has a rather straightforward solution—lots and lots of education, outreach, and more positive stories.

Bats have been living close to us for centuries. Every other household has a bat somewhere hiding in a corner. The reason why we have rarely got diseases from them is because they know how to maintain ‘social distancing’ better than we do.

If we just learn to leave them alone and follow some basic hygiene rules, we can drastically reduce the chances of getting infected. This includes masking up when close to a bat colony, washing our hands after handling them or their faeces, staying away and keeping pets away from their faeces.

Bats have been living close to us for centuries. Every other household has a bat somewhere hiding in a corner. The reason why we have rarely got diseases from them is because they know how to maintain ‘social distancing’ better than we do.

A Round-eared Tube-nosed Bat (Murina cylotis) that was caught in a deodar forest being photographed and recorded inside a forest rest house. Photo by Rohit Chakravarty.

What are some of the most common misconceptions about bats?

They get entangled in our hair (they have better things to do!).
They bring bad luck (they’ve given me my PhD).
They drink blood (insects are tastier than our stale, antibiotic, fertiliser, and hormone-soaked blood).
They are birds (no, they give birth to live young ones and produce milk).
They are flying mice (they are more closely related to cows and whales than to mice).

More about the guest

Rohit Chakravarty is Project Manager, India-Nature Conservation Foundation (NCF) and Bat Conservation International (BCI). He finished his masters’ dissertation on bats in the Andaman Islands in 2014 and found his way into the Himalayas where Nature Science Initiative (an NGO run by his colleagues Dr. Raman Kumar and Dr. Soumya Prasad) hosted his bat call library project and was instrumental in helping set it up. Through introductions to their field assistants in the Van Gujjar tribe, some of their field assistants became his as well. Zareef Khan Lodha, Baseer Baniya, Saddam Husain Lodha, and Shamshad Ali Baniya have been part of his team between 2016 to 2021.

For Bat Call Identification 101, read Rohit’s piece here, and learn the difference between spectrograms and sonograms, and how not to mistake a call library for a call centre.

You can find Rohit on X/Instagram @paintedbat

See his work here.