Call from cave

Bats, largely elusive till now, are slowly revealing their secrets as scientists record and analyse their calls

By Vibha Varshney
Published: Saturday 15 November 2014

Eastern barbastelle bat, known to be indigenous to the Himalayan foothills, was recently found in the Western Ghats

Unlike their terrifying reputation, bats are key species that maintain the ecosystem by helping in pollination, controlling insects and keeping rodent populations in check. But these guardians of the night are sensitive to changes in the environment. With their habitats being fast destroyed and food sources shrinking, monitoring them is a good way to know what is happening to the environment.

But studying them has been tricky since bats are difficult to catch. Researchers are now relying on a unique method to understand the nocturnal species better. Bats make pips and squeaks and listen to the echoes to visualise their environment. Each species has its own distinct echolocation call. An increasing number of scientists are recording and analysing these calls to understand bats’ distribution behaviour. They say the method is not only faster and suitable for larger areas, it also protects the species from unintentional transfer of diseases, such as white-nose syndrome caused by a fungus during capture. Such studies also indicate the changing behaviour of bats in changing environments.

Using echolocation calls, researchers from Israel’s Ben-Gurion University and the UK’s University of Bristol have found that bats in Israel’s Arava and Judean deserts are changing their foraging methods during extremely hot and dry summers, when finding prey becomes difficult. This phenomenon was accompanied by a change in calling behaviour. Bats that usually forage on the ground and emit sounds at 75 decibels, changed their diet to flying insects. Their calls also changed to 119 decibels and resembled those bats that prey on flying insects. The study was published in the Journal of Experimental Biology in September.

While echolocation calls are an effective tool, a database of bat calls is required for cross-referencing. Scientists in Europe have developed one such tool, iBatsID, which has recorded calls of 34 European bat species.

The tool is available online for free. Researchers are now trying to prepare a database of calls for India’s Western Ghats. The biodiversity hot spot hosts 43 per cent of the 117 bat species found in the country. But over the years, the region has become densely populated. Portions of the hills have been blasted to make space for settlements and buildings have come up near caves.

It is imperative to understand the impact of these changes on bats. Between 2008 and 2013, researchers from the UK’s University of Leeds, Bengaluru’s National Centre for Biological Sciences and Mysore’s Nature Conservation Foundation of India studied bats in the Valparai plateau of the Anamalai hill range. They captured bats from fragmented forests, coffee, tea and cardamom plantations, along rivers and from roosts in tunnels and caves. They were identified and their echolocation calls were recorded. The researchers found that in some cases, calls of the same species differed from those published in other areas. The team recorded echolocation calls of five species for the first time and identified a species, Eastern barbastelle, which was so far thought to be restricted to temperate forests. The researchers also found two more species that were not thought to be found in the area. “This underlines how much we still have to learn about the distribution and ecology of bats,” says Claire Wordley of the University of Leeds’ Faculty of Biological Sciences and lead author of the study (see interview). The study was published in the latest issue of Acta Chiropterologica.

Another group of researchers is also recording bat calls in Kudremukh National Park. Their findings show that species of bats could be classified accurately to the extent of 91.7 per cent based on their calls. The study was published in the August 25 issue of Current Science. Lead author, H Raghuram of The American College, Madurai, says, mapping echolocation calls of species to their respective sites will give an idea where they live. So if you want to construct a road or wind mill, it can be planned to avoid areas where bats live. This is one way of conserving them, he adds.

`We know little about bats in South Asia'

After recording bat calls for five years in the Anamalai Hills of the Western Ghats, Claire Wordley, a PhD student at School of Biology, University of Leeds, UK, has prepared a database of the calls of 15 bat species. She tells Down To Earth how the database can help protect the species

Claire Wordley

Is a library of echolocation calls of just 15 species enough to monitor bats in the Western Ghats whichharbour more than 50 species?

No. This library will enable effective monitoring of bats only in a small area of the Western Ghats, say the Anamalai Hills. But if researchers recording such calls in other areas of the Western Ghats start publishing their database, it will help identify bat species and monitor their behaviour across the entire Western Ghats.

Is there any special significance of the bat species you studied?

We chose an area of high biodiversity and recorded all bat species we could catch in that area. They are a mixture of fruit bats and insectivores, and play different but important roles in the ecosystem. Fruit bats are important for pollination and dispersing fruits, while insect-eating bats are vital for pest control. Some species we studied, such as the Lesser Woolly Horseshoe bat (Rhinolophusbeddomei), are rare and are interesting from the point of view of conservation. Others, such as Tickell's Bat (Hesperoptenustickelli), had not had their echolocation call recorded before anywhere in the world. So these calls will be useful to other researchers.

Why is finding the Eastern barbastelle bat in this area important?

The Indian subspecies of Eastern barbastelle was a truly exciting find because it has only been reported from the temperate forest in the foothills of the Himalayas, 2,000 km from where we found it in the steamy rainforests of tropical southern India. The species was thought to be at risk from deforestation in many areas. So finding the species in the Western Ghats provides a new conservation opportunity. It also underlines how much we have to learn about bats in South Asia.

How do you plan to take the study forward?

The call library we published here enabled several projects, such as building habitat suitability models for species, looking at changes in species composition between forest and different plantation types, and looking at the functional diversity of bats in the study area. These studies improve our understanding of conservation needs of different species. We also aim to discuss our findings with people living and working in the Anamalai Hills, such as landowners and schoolchildren, to instill a positive approach towards bats and describe to people the amazing wildlife that is easy to miss because it comes out at night.

Subscribe to Daily Newsletter :

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.