In southern India, near the Bandipur Reserve, a hungry Asian elephant walks towards a farm in search of food. This region has one of the densest populations of Asian elephants in the world. During the dry season, when food is sparse in the forest, they find the surrounding farmlands irresistible. Conflict between farmers and crop-raiding elephants is a huge problem here. It costs some people a third of their income and, every year, it claims the lives of 400 humans and 100 elephants.
But this particular elephant doesn’t get close enough to farmland to cause a problem. Tripping an infrared beam that’s laid across the path, it triggers a nearby speaker. A low growl emerges, deep and loud. It’s the sound of a tiger, and the elephant knows it. Silently, it retreats.
The recorded growls were set up by Vivek Thuppil and Richard Coss from the University of California, Davis, who have been testing them as ways of diverting elephants from Indian farms. “We’d heard anecdotal reports that elephants are scared of tigers, and that farmers had used playbacks of growls to deter elephants from their fields,” says Thuppil.
They began by recording the growls of a leopard and a tiger at the Bannerghatta Zoological Park. In their paper, they write:
“To engender growling, both cats were agitated similarly when the keeper entered their cages and banged a stick repeatedly. We did not repeat this procedure with other individuals owing to the potential danger involved.”
You don’t say.
The two cats sound very different. Even when equalised, the tiger’s growl is deeper and feels louder, while the leopard is raspier and guttural. “Every human we’ve spoken to says the leopard growl sounds scarier,” says Thuppil.
The elephants clearly think otherwise. When Thuppil and Coss played tiger growls from their hidden speakers, elephants immediately backed away, slowly and quietly.
If they played leopard growls, they trumpeted and grunted, investigated the surrounding area, searched for sounds and smells, and kicked the dirt. Only then did they walk away.
Their reactions are prudent. Tigers are the greater threat, since they’ll occasionally kill elephant calves. Farmers find the body of a half-eaten calf at least once or twice a year, and scientists have found elephant remains in tiger droppings. But leopards are smaller and less powerful and there are no reports anywhere of them killing elephants.
However, the elephants might not be weighing any risks. Thuppil says that tigers will actually growl to deter an approaching elephant, while leopards would just retreat. Their agitated behaviour upon hearing the leopard growl might just be a reaction to something new. Still, they can clearly distinguish between the two types of sounds.
It’s not the most surprising result, given other studies about elephant behaviour. African elephants, especially the older matriarchs, can distinguish the sound of male lions, which pose the greatest threat to their herds. They can also smell the difference between clothes worn by Massai hunters who kill elephants, and Kamba cattle-herders who do not. Clearly, these are intelligent animals that can react in sophisticated ways to different degrees of danger. Still, no one had shown that they can tell the difference between the sounds of two big cats.
The growl playbacks worked to a point, but they weren’t a sustainable solution. “If you have elephants that come back repeatedly, they tend to habituate,” says Thuppil. “They learn that there’s no real threat.” He and Goss are now trying to adapt the playbacks to stop the elephants from getting accustomed to them. “One idea is to have a dynamic playback system, so the location of the sound keeps changing depending on where the elephant is. That would simulate a moving predator rather than a stationary one.”
Some people try to deter crop-raiding elephants by digging deep elephant-proof trenches, but rain can often transform these into gentle-sloping dips. Electric fences are commonly used, but elephants can destroy these with their tusks or by pushing trees onto the fences. Some farmers sit in tree platforms and harass the elephants with drums, shouts, torches, flashlights, or fireworks, but the agitated animals can sometimes run amok.
The imperfect nature of these solutions has prompted conservationists to search for alternatives. In Africa, Lucy King from the charity Save the Elephants has been using beehive fences to deter the giants. African elephants might stand up to lions, but bees can sting them in their eyes, behind their ears and inside their trunks. If they hear buzzing, they will flee. As a bonus, the fences also provide local people with a source of income: Elephant-Friendly Honey. You can find out more about King’s project here.
Reference: Thuppil & Coss. 2013. Wild Asian elephants distinguish aggressive tiger and leopard growls according to perceived danger. Biol Lett http://dx.doi.org/10.1098/rsbl.2013.0518
Thuppil & Coss. 2012. Using Threatening Sounds as a Conservation Tool: Evolutionary Bases for Managing Human–Elephant Conflict in India. Journal of International Wildlife Law and Policy http://dx.doi.org/10.1080/13880292.2012.678794