Dog Whistles & Subwoofers

Last Friday’s horrific earthquake and tsunami in Japan got me thinking about the last major tsunami in memory, the cataclysmic Indian Ocean tsunami of 2004. Much was made of the fact that, though entire towns were leveled by the flood, very few wild animals perished. It seems that about eight hours before the tsunami hit the shore, there was a massive migration of animals to higher ground. What tipped them off? The infrasonic sound of the approaching wave rumbling under their feet. And when I think of infrasound, the first animal I think of is the giraffe.

Really? I don't remember saying anything.

Why the giraffe? Why not a well-known basso profundo like the elephant? I have written about giraffes before, mainly in the context of how incredibly gay they are. But I’ve never written about their songs.

It was thought for centuries that giraffes were practically mute. Like rabbits, they were only known to make sounds in times of distress or courtship: whinnies, bleats, snorts, coughs, and even the occasional groan, mew, or bellow. But it was presumed that, for the most part, giraffes were simply very tall wallflowers. Then, in 1998, a bioacoustician named Elizabeth von Muggenthaler borrowed some high-tech equipment and discovered that giraffes are actually extremely talkative. They’re simply having a conversation below our range of hearing.

That giraffes are basses should have been obvious from the necks.

Infrasound is regarded as sound below 20 Hertz, a deep rumble that doesn’t register to the human ear. Elephants use infrasonic calls to communicate with each other over distances of up to six miles, carried through the earth itself. This is particularly important to social creatures that require massive amounts of space. They use these low-frequency noises not unlike birds use song: to avoid confrontation with other herds, and to find a mate. Female elephants have a two-year gestation period, and spend the next two years nursing the calf, so they are only in estrus for a few days every four or more years. The young males in musth, a period of hyperactive, irritable horniness, are able to find receptive females from miles away by the love calls they send booming into the ground.

When she calls, I musth come.

American Alligators, too, use deep bass to woo females, as well as to establish hierarchy between males. The standard alligator pick-up line is audible to human ears, but there’s an infrasonic wave beneath it that carries through the swamp water. They have evolved special sacs in their throats to amplify this sound, and when it makes its bellow, the water around its jaw “dances” and jumps with the vibration. The only problem with this strategy is that many things produce ultrasound. Storms, waves, avalanches, earthquakes, the aurora borealis and ice floes all produce infrasonic frequencies. Calving ice floes may be rare in Florida, but other sources of infrasound are relatively common there: cars, motorboats, and space shuttles. It was discovered that the sounds of spaceship engines at Cape Canaveral are upsetting the local alligator mating season, causing the bull gators to think that one incredibly bad-ass male was looking for a fight and setting off an aggressive, territorial chain of bellowing. In Israel, fighter planes creating sonic booms over the local zoo have been making the alligators horny; a fighter jet breaking the sound barrier overhead triggers an immediate mating response.

Is it love, or just the sonic boom from a war machine?

Another lonelyheart with a tremendous voice is the rare Sumatran Rhinoceros, the smallest and most vocal of the 5 species of rhino. This species, of which there are less than 300 in the wild, is a descendant of the extinct woolly rhinoceros, and as such is covered with a course, red fur. Like the elephant, it is a very large animal with a very large appetite and therefore requiring a very large territory, and unlike the elephant, it is generally solitary except when it is time to breed or rear young. So Sumatran Rhinoceroses almost constantly warble across the distance with a series of infrasonic signals called eeps, whales, and whistleblows. The “whales” are called as such precisely because they sound like whalesong. For comparison, here are the long and short songs of the Sumatran Rhino, or at least the part that is audible to us, and here are the vocal stylings of the humpback whale. Rhinos may be a long-lost sister taxa to whales, so it’s unknown whether the similarity to whale vocalizations is indicative of convergent evolution or an ancestral song.

The problems start when rhinoceros infrasound accidentally attracts humpback whales.

The hippo and the okapi also make use of infrasonic wavelengths to broadcast their feelings, the tiger uses infrasound in its roar to momentarily paralyze its prey with fear, and many birds, such as pigeons, use the infrasonic whistle of the wind sliding against mountains and canyons in order to navigate, each peak and valley vibrating with a unique note. It is believed by some experts that the purr of cats, both house and larger, developed as a way of healing bone tissue; infrasound is effective at expediently healing human and bovine bones and ligaments, and the purring of large cats is full of infrasound. But what of the ultrasonic animals, those who function on a frequency above the limit of human hearing? Cats, dogs, certain fish, and a wide array of other animals can hear ultrasound, usually defined as 20 Kilohertz or more. Dolphins and bats famously use ultrasonic chirps to echolocate and communicate. But it was only recently discovered that small rodents not only produce ultrasonic noise, but can also sing. When it smells the pheromones of a female in heat, the male mouse issues a series of chirps that are unmistakably musical, not unlike birdsong. The precise reason for this is unknown, as it’s never been shown to attract a mate in its natural habitat. Here it is, with its rhythm unaltered but its pitch lowered by four octaves, and here again, both lowered to an audible pitch and slowed down.

A bioacoustician prepares to experiment on the musicality of mice.

It is more than a cute aphorism that there is a song on the wind, or that the hills are alive with the sound of music. It is no hippie cliche to say that animals listen to the Earth, for they literally speak through it at times, and can appreciate the cello of tectonic rifts moving past one another, the harmonium of lakes as the wind blows across them like crystal jars, and the xylophones of vibrating skyscrapers. The world, it seems, is full of the songs and conversations of animals and natural phenomena both above and below the range of our hearing. We only hear a fraction of the sounds that go on all around us, just as we are not able to see the stars in the daytime. The music passes through us like songs on a stray radio wave. When you listen to the silence, you are merely meditating on your own deafness. And when you go to the zoo, the giraffes talk about you behind your back. (And are probably mocking you, short stack.) It is possible to feel infrasound, but it takes some practice to know what it is; infrasonic vibration tends to give people a feeling of nausea, unease, discomfort, or fear. The same can be true of animals, in that the groan of the earth before a quake makes many animals anxious or fearful. It is too early and untimely to ask whether animals sensed the earthquake in Japan before it struck, but presuming the country doesn’t face far more serious catastrophes in the coming months, I don’t doubt that we’re likely to hear many anecdotal stories about psychic animals. It happens after almost every quake. Animals may mistake sonic booms for pillowtalk, but they know well what the Earth sounds like when it moves. No living thing could be so loud. Right?

The Australians beg to differ.

Let’s go back to Dr. von Muggenthaler for a minute. Commissioned to search for “Champ,” the cryptozoological creature in Lake Champlain between Vermont and New York who is the American analogue of the Loch Ness Monster, Dr. von Muggenthaler found something else entirely. Her equipment picked up the distinctive clicks of three animals using ultrasound sonar. But no dolphins are known to live in this freshwater lake. What is navigating its murky depths? We have no idea.

ECHO: Meet the Scientist: Lake Champlain — Home To A Mystery Animal? from Chris Middings on Vimeo.

The good stuff starts at 18:00.

The ocean is similarly full of such mysterious sounds. Creaks, whistles, and moans carry further in the water than in air, but we believe we’ve catalogued most of the whales’ repretoires, and still there persist ultra- and infrasonic noises in the ocean that no one can explain, yet seem vaguely biological. The most famous of these is a sound in the Pacific Ocean known only as The Bloop. First picked up by Navy microphones in the summer 1997, The Bloop seems to emanate from the coast of southernmost South America in the Pacific Ocean. What’s more, its audio profile fits that of a living animal.

The Bloop, sped up to 16 times its normal rate.

The hitch is that the sound travels over 3,000 miles, which is far, far louder than the loudest animal alive, the blue whale, can achieve. (At 188 dB, a blue whale actually produces a louder sound than an AC/DC concert, the loudest of which topped out at a mere 130 dB. A Navy jet reaches about 140 decibels, which happens to be the level at which the eardrum is irreparably damaged. A space shuttle launch reaches 170 dB. I am pretty sure a blue whale’s 188 dB will liquify the human brain. The Bloop has been estimated at 246 dB.) It seems unlikely that any animal could be large enough to produce such a massive sound, and indeed there have been other theories, from calving ice floes to underwater volcanoes. Yet the question remains, what could cause such an infrasonic burp? Might there not be something even larger than a blue whale lurking in the ocean’s depths, singing a deep and desperate love song?

It gets less sentimental when you think about it.