Call of the wild: How science is learning to decode the way animals communicate

This week it was revealed the babbler bird communicates using language

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The Independent Online

The deathwatch beetle goes “tick, tick, tick” in the dead of night as it bangs its head against an old oak beam. A lone wolf howls eerily from the forest depths, while the skylark ascending sings its uplifting chorus from the majestic height of a blue summer sky. These are just some of the myriad sounds made by animals in their quest to communicate with fellow members of their species. The world really is alive to the sound of living creatures – which can, in turns, feel like music or menace to the human ear.

This week scientists demonstrated just how intricate these calls of nature can be when they published details of a study showing that the chestnut-crowned babbler bird of Australia communicates in a simple form of language.

The babblers combine different sounds that on their own are meaningless but when used together in a particular sequence convey specific messages – similar to the individual sounds or phonemes of human language. No less interesting is the shear breadth of noises made by the rest of the animal kingdom, whether it is the deep, infrasonic rumble of an African bull elephant in musk or the high-pitched, ultrasonic sound of the grasshopper – both of which fall well outside the opposite ends of the human auditory range.

 

In their attempt to understand this natural cacophony, scientists have for decades been recording and analysing the surprisingly varied sounds of nature. They even hold a regular international conference on “acoustic communication in animals” to compare notes and exchange thoughts on everything from the territorial call of a male elk to the incessant whine of a female mosquito in search of a blood meal.

The latter noise is after all the “most hated sound known to man” according to Peter Belton of Canada’s Simon Fraser University in Burnaby, British Columbia, who has made a special study of the female mosquito’s wings. In fact, he has made a scale model of them to work out just why they produce such an annoying sound.

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The Skylark's song is composed of 300 syllables and marks a breeding pair’s territory (Getty)

It turns out that the hateful whine is due to the harmonics produced by the “click” of the mosquito’s thorax as she beats her wings up and down – in stark contrast to the sensory pleasures felt by the perfectly-tuned antennas of the male mosquito, which apparently hears nothing but a pleasant “flute-like” warble. Just as beauty is in the eye of the beholder, music is in the ear of the receiver. For humans, the sound of a songbird is just that – a sweet melody. We even have a musical name for that cacophony of noises we hear first thing in the morning: the dawn chorus.

A skylark ascending is a sound of joyous delight. But in fact, like many bird songs, it is deadly serious game of maintaining territorial integrity, with each breeding pair of ground-nesting skylarks staking its claim of their particular patch of grassy down.

Males produce long, complex songs composed of more than 300 different syllables. Interestingly, neighbouring pairs of skylarks tend to share several sequences of syllables, a bit like a local dialect, while strangers from further away share few if any.

Scientists from Paris University in Orsay have shown that if you mix up the songs of skylarks so that a neighbour starts to sing like a total stranger, it is likely to send a skylark mad with rage. It seems that skylarks are less aggressive towards close neighbours when territorial boundaries are established than to total strangers – an ethnological phenomenon known as the “dear-enemy effect”, which helps to keep the skylark peace.

Of course, not all bird song is about marking territory. Much of it is about marketing for a mate, and once the vocal self-promotion has achieved a viable pair bond, there is a separate medley of tunes to maintain it, such as the “duetting” songs of the male and female kiwis, the nocturnal icon of New Zealand that mates for life and keeps good marital relations with sweet, night-time whistle duets between the sexes.

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Elephants' low-frequency rumble can be heard by others miles away but is inaudible to humans. Scientists think they transmit through the ground (PA)

Not so romantic is the howl of the wolf. Dramatists often use it to portray lurking menace, when in fact the wolf howl is more about missing your best friend according to Francesco Mazzini and colleagues at Austria’s Wolf Science Centre.

In a study published in 2013, the researchers showed that wolves howl when one of their number goes missing from the pack, but they howl even more when the missing wolf is a close friend – such as playmate or partner. The findings were seen as important because they indicated something much deeper about animal communication.

For a long time, scientists thought that animal vocalisation was an automatic reflex guided by the physiological state of the animal, rather than something under more direct control, like the conscious actions of human speech.

The wolf study on howling indicated that it was not just about a missing pack member, but about an individual wolf’s deeper relationship with the missing wolf.

As the researchers concluded: “This provides support for the hypothesis that wolf howling is potentially a strategically employed vocalisation with the goal of ultimately promoting contact with important individuals.” In other words, a wolf’s howl is about “thinking of you” rather than menace.

Sound of course is a wonderful way of communicating a range of signals over long distances. The wolf’s howl can carry for between six and ten miles on a still night, but this is nothing compared to the distances that sound can travel underwater.

Sound in the ocean not only travels further than in air, it travels faster and with less attenuation – reduction in strength.

Just as in air, sound underwater can convey a range of messages and signals depending on its frequency or pitch, amplitude or loudness and periodicity or regular variation in frequency and amplitude.

Whales, dolphins and porpoises are masters of this underwater genre, having evolved from terrestrial mammals with auditory systems tuned to the transmission of sound waves through the air rather than water.

The blue whale, the largest animal on earth, can emit low-frequency rumbling sounds that can be detected half way around the world, while the sperm whale has adapted echolocation “clicks” originally used as a form of underwater radar but now used as a way of keeping a family clan together – in fact, individual clans can be distinguished by the kind of vocal “coda” they use.

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The intricate songs of Humpback whales have been described as the most sophisticated vocalisations in the animal kingdom (AP)

Perhaps the most intricate vocal communication in the ocean is displayed by the humpback whale, whose calls have been compared to birdsong because of their complexity. They were first recorded at the end of the 1960s – by American military personnel listening for Russian submarines – and their level of sophistication astonished scientists, leading some to say they are possibly the most complex vocalisations in the animal kingdom.

The humpback whale songs follow a hierarchical structure, with the base notes of the song emitted as single uninterrupted emission of sound that lasts a few seconds. The humpbacks vary these notes in frequency and the pitch may go up and down on the same note, at the same time as varying in amplitude or loudness.

Little wonder the songs of the humpback were sold as an LP in the 1970s, when they achieved an almost mystical status. One recording  even got onto the golden record of earthly sounds sent on board the Voyager spacecraft launched in 1977. Humpback whale songs later appeared as a theme in Star Trek IV, when an alien probe is sent to contact the last remaining members of the species.

In reality, of course, humpback songs are to do with the kinds of things seen in other mammals and birds. Males sing most during the breeding season, so the songs are almost certainly connected with attracting a mate or keeping her away from competing males. The complexity of the songs may have evolved as a result of female choice: the most intricate songs are a sign of male fitness that females will choose in preference to the less intricate songs of other, less fit males.

At the other end of the complexity scale is the simple head banging of the African termite. Soldier termites guarding the nest communicate an alarm signal to one another by banging their heads against the walls of their underground tunnels – a head-splitting 11 times a second. Like tribal drums, the message is picked  up by other termite soldiers, which begin their own head-banging until the entire colony is vibrating to the communal alarm of collective head-banging.

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The howl of the wolf is a call by the pack when one of them goes missing – and is louder when the missing wolf is a close ‘friend’ (PA)

Which brings us back to the deathwatch beetle, another head-banger.

Although no-one knows for sure, it is likely that this solitary night-time activity is about looking for a mate rather than raising the alarm.

The simple love song, composed of a series of fast ticks, may not have the mysterious complexity of the humpback whale, but they are presumably no less alluring to the female of the species.

Sex and rock’n’roll have a long evolutionary history, as any head-banging teenager ought to know.

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