Trunk Emits Infrasonic Calls

a young gray elephant lifts its trunk in a tall green grass field

Biological Strategy

Elephants

AskNature Team

Image: Birger Strahl / Unsplash / Some rights reserved

Sense Sound and Other Vibrations From the Environment

For living systems, sensing sound and other vibrations is important for communicating and detecting conditions within their environment. Living systems must locate a signal’s source so that they can move toward it (such as when it is food or a potential mate) or away from it (such as when it is a predator). To prompt an appropriate response, living systems must sense these signals, recognize their amplitude or volume (which is sometimes very low), and determine their direction. Living systems must be attuned to signals relevant to them and able to distinguish these from irrelevant sounds to avoid expending unnecessary energy. For example, owls’ ears are asymmetrically placed. This enables them to detect sounds more accurately, which helps them locate small prey at night and avoid wasting energy chasing down irrelevant sounds.

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Send Vibratory Signals

Some living systems use vibrations to communicate, as well as to detect conditions within their environment. Some vibratory signals are very high frequency, such as those of a carpenter bee’s wings that cause flowers to release pollen. Other signals are very low frequency, like those used by elephants to signal to other elephants through the ground. Water, air, and solids present different challenges for transmitting vibrations. Living systems must therefore generate vibrations that move best through the particular medium. For example, a water skipper stands atop water and creates vibrations that circle out from it in ripples, signaling to other skippers to stay out of its feeding area.

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Send Sound Signals

Many living systems send auditory signals to communicate with others, including to attract, announce, or warn. These sounds must be audible to the intended recipient in a variety of conditions, such as in wind, water, and solids. As a result, each living system has specific sounds best adapted to its environment. For example, some birds live in loud habitats, like those alongside noisy streams or in windy areas. These birds use sound frequencies that can be heard by other birds over competing environmental noises.

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Nasal passages of elephants communicate by emitting vibrations that cause infrasonic sounds.

“The elephant was the first land animal shown to communicate infrasonically–a landmark discovery that came from two independent observations. In 1981, Kansas University scientists Dr. Rickye Heffner and Dr. Henry Heffner were surprised to discover that elephants could detect sound frequencies as low as 17 Hz, which were within the infrasonic range. But why should they be able to do this? What purpose does it serve?”

This sound was described by Dr. Katherine Payne from Cornell’s Laboratory of Ornithology as, “I repeatedly noticed a palpable throbbing in the air like distant thunder, yet all around me was silent.” (National Geographic article, August 1989). The sound reminded her of standing next to the largest organ pipe in her church when the organ blasted out the bass line in a Bach chorale.

Dr. Payne and others recorded elephants and found that “[W]ithin one month 400 separate calls had been recorded–three times the number of calls heard by the researchers in the sonic range. Analyses showed that the elephants emitted short calls at a frequence range of 14-24 Hz, which lasted for 5-10 minutes, over a period of 10 minutes.

“The tam also uncovered an important visual clue to the production of these secret sounds by elephants. When an elephant is volcalizing infrasonically, the skin on its brown flutters, vibrating gently as air passes through to its nasal passages…Since infrasound travels over long distances, it is useful in this regard. Subsequent studies have shown that elephants in Africa can hear calls from as far away as 2.5 miles (4 km) during the day, whereas in the evening this range can extend to up to 6 miles (10 km) as a result of temperature inversions in the atmosphere that make sound travel farther.” (Shuker 2001:25-27)

Other infrasound communicators: okapis, giraffes, African and Asian elephants, rhinoceroses, hippopotamuses, alligators, crocodiles, capercaillies, and baleen whales.