The inaudible identities of Western Ghat bats

Claire Wordley and her team were looking for bats in Valparai in the Anamalai range of the Western Ghats. A furry critter sitting absolutely still in the net took them by surprise. “I realised it was a Barbastelle bat”, Wordley says. “I’d only seen them in Europe but they have such distinctive faces – ears meeting over the head and nostrils on top of the nose — I could tell the genus right away.”

Wordley was right. Cross checking with a guide book, she and her team confirmed that the Eastern Barbastelle (Barbastella leucomelas darjelingensis) was distributed in northern India, Pakistan, Nepal and Afghanistan. Though the Western Ghats were a long distance away from the cool temperate Himalayan forests, a recording of the bat’s call further confirmed it was indeed an Eastern Barbastelle. This was the first time the species was being reported from southern India far from its known territory.

Bats are usually monitored by laying out extremely thin, almost invisible nets called mist nets. Researchers then identify them before releasing – it’s a time taking process. Alternatively, bats can be identified by their calls. Bats use ‘echolocation’ – they emit sounds in the ultrasound range and use the sound echoed back to locate prey or obstacles on their flight path. These calls are beyond the range of human hearing but appropriate audio recording equipment can pick them up.

The first step toward using calls for monitoring is to build bat call ‘libraries’ for each area. This is what Wordley and her team from University of Leeds, UK, the National Centre for Biological Sciences, Bangalore and the Nature Conservation Foundation, Mysore, set out to do.

“It is a good idea to create a bat call library taking into consideration the correct taxonomic identification of the species and associating the call parameters to it”, says Chelmala Srinivasulu, a zoologist from Osmania University not involved in the study. “Bat calls that overlap in numerical values of call parameters cannot be distinguished. For such cases we need to study the sonograms and pay attention to harmonics and other characters.”

The team focused on bats from the Western Ghats, which they have been sampling at Valparai from 2008 to 2013. They captured the bats, identified them and recorded their calls on release. This study is the first to build an echolocation library and analyse bat calls from the southern Western Ghats. For bats which call at a constant frequency, one recording was sufficient to identify them with 100% accuracy. For bat species with frequency modulated calls (starting at a high frequency and sweeping down to a low frequency), five measurements were taken per call. They were identified with an accuracy of 90%. Of the 16 bat species known from this latitudinal belt, the study recorded eight¹. The researchers also found that bats of the same species called differently in different areas, for instance the Rhinolophus rouxii (Rufous Horseshoe bat) and Hipposideros pomona (Pomona Roundleaf bat).

“There are indications in literature that bats call at different frequencies due to local conditions. They may call at lower frequencies with increased humidity or at higher frequencies in denser forests”, Wordley says. “However, in south India, it has been shown that a horseshoe bat thought to be just one species was in fact three species, genetically distinct with slight morphological differences and calling at different frequencies. I suspect that a lot of the bat species we think of across Asia as being one species will turn out to be very similar looking species, or subspecies that perhaps are separated geographically and no longer meet naturally.”

Wordley also feels bats are under-studied in India, when compared to animals like tigers and elephants. “As the study of bats increases in the country, there will be more exciting bat finds. The recently set up Indian Bat Research and Conservation Unit will hopefully lead to more students caring passionately about these fascinating little mammals”, she adds.