Elephants Call Long-Distance After-Hours
for National Geographic News
|March 3, 2004|
African elephants have perfected the art of calling long-distance. They make most of their calls at night, when it is cooler and sound travels farthest.
Elephants are highly social animals, and they snort, scream, trumpet, roar, and rumble to communicate with one another. Low-level conversations among family members continue throughout the daya calf may rumble to its mother to stop so it can suckle, for instance. Close to 70 different sounds or "messages" used by elephants to keep in touch have been identified.
"Messages include both long and shorter-distance calls," said Michael Garstang, a meteorologist at the University of Virginia, Charlottesville.
"Many of the rumbling calls occur at the level of infrasound, a very low-frequency rumble below the audible hearing range of humans," he said. "Humans can hear the upper end as a rumble, although you're not hearing it in your ears, it's more like feeling the vibrations in your diaphragm."
The frequency of sound is measured in hertz (Hz). The infrasonic range is roughly between 1 and 20 Hz. Infrasound can travel long distances; however, atmospheric conditions can severely limit the distance.
Garstang and his team collected and analyzed more than 1,300 calls made by elephants on the Namibian savanna, where daytime temperatures frequently reach 120 degrees Fahrenheit (49 degrees Celsius), and winds blow at up to 20 miles an hour (32 kilometers an hour).
"Calls made when atmospheric conditions are optimum can be heard over at least 110 square miles [285 square kilometers]," Garstang said. "Wind gusts and shimmering heat waves can break up sound waves and reduce that distance to less than one square mile [2.6 square kilometers]."
Garstang found that 96 percent of the infrasound calls designed to travel long-distance occurred during the hours of dusk and dawn. Ideal atmospheric conditions occur near sunset and sunrise, when temperatures drop and the winds are quiet. Calls made during these optimum times could be heard up to 6 miles (10 kilometers) away.
Listening to Elephants
The ability to make themselves heard over long distances is crucial to elephant survival.
Elephants live in family groups of closely related females and their young, led by a matriarch. The males wander alone or in very small groups of other males. From an evolutionary point of view, one of the most important long-distance calls signals a female's readiness to mate.
"When the female is in estrus, breeding bulls that are 35 to 55 years old and in their prime can be many miles away," Garstang said. "The female wants the biggest and strongest male she can find. If her call went less than a mile [1.6 kilometers], the chance of her finding a really good male would be close to nonexistent."
A call that extends over a range of a hundred square miles (260 square kilometers) or more improves her odds considerably. Maintaining contact with other groups within their home range is also essential.
"Elephants live in a fission-fusion society, which means that close relatives frequently come together and split up again," said Joyce Poole, zoologist and scientific director of the Savanna Elephant Vocalization Project and the Amboseli Elephant Research Project in Kenya. "Members of a family and bond-group maintain contact with one another over distance by using contact calls. These powerful low-frequency calls are clearly meant to travel long distance."
Long-distance communications also help ensure survival in an environment of limited resources. An adult elephant can consume several hundred pounds of foliage a day. By the end of the dry seasonwhich extends from April to September in Namibiafood, nutrients, and water are extremely scarce.
Long-distance communication allows groups to maintain a certain amount of separation from one another. Groups traveling over the path of a group that has already grazed foliage to the nubbin would starve.
Garstang speculates that an evolutionary imperative might have led elephants to communicate during the best environmental conditions. Poole, who has been listening to elephants for several decades and has identified roughly 70 messages, is not so sure.
"It's true that elephants vocalize more in the early mornings and in the evenings, but this also happens to be a time of day [in Amboseli at least] when they are interacting more," she said.
"In the morning they are waking up and gathering together for the trek to their feeding grounds. In the evening their tummies are full and they have the extra energy for interacting as they move away from their feeding grounds.
"The increase in communication at these times of day isn't necessarily because they want to communicate long-distancemany of the calls are meant for close-distance communication. Nevertheless all calls will have a wider audience."
Poole notes that as habitats and social circumstances change, so too do the reasons for communicating.
"In different populations, the frequency of call types varies," she said. The extreme conditions in Namibia may explain the differences Garstang and I have observed," Poole said.
Implications for Conservation
Understanding what elephants hear and communicate has implications for conservation efforts.
"There's a tremendous amount of sound information being transmitted in nature," Garstang said. "In highly social animals like elephants, it's a world we're just beginning to explore, one with enormous connotations. We don't know what kind of impact the noise [humans] create may be having. "
In Amboseli elephants must contend with four diesel generators and scores of minibuses, all of which interfere with their ability to communicate, Poole said.
"One musth male expressed his displeasure by musth-rumbling every time a minibus departed from the lodge two kilometers [1.2 miles] away," Poole said. Males in musth actively seek mating opportunities and become much more aggressive toward other bulls.
Environmentalists also worry about the impact sonar testing conducted by the U.S. Navy might have on whales and other marine animal populations. Concerns include damage or destruction to hearing, disruption of calving and breeding activities, loss of feeding and nursery habitats, interference with their navigational senses (leading to beaching), and separation of migrating calves and their mothers.
"It's believed that elephants can hear storms as much as 100 to 150 miles (160 to 240 kilometers) away," Garstang said. "When culling was being done in some of the parks, the elephants could clearly detect and identify the thump-thump-thump sound of the helicopter blades from 80 to 90 miles (130 to 140 kilometers) away, identify it as danger, and take off in the opposite direction."
During the 1990s some elephant herds in Africa became so large that government-hired hunters flew over the parks and shot elephants to reduce the size of the herd.
"Elephants' 'vision'through low-frequency communicationis larger than ours," Poole said. "We need to take this larger vision into consideration when setting boundaries for national parks, establishing corridors between protected areas, and in considering cross-border movements and protection."
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