January 24, 2011 | 6
It’s loud out there. All that banging and driving and dumping and flying and building we do is making the world noisier and noisier. While humans don’t seem to mind the sounds, and when we do we just put in our earplugs – animals are dealing with all the racket we make in interesting ways.
All environments have some kind of noise. Even before people animals had to deal with ambient sounds like rain, rivers, waves, wind and other animals’ calls. But, like most things, humans have come along and drastically increased the amount of noise out there.
On land, urban noise comes from highways, trucks, construction, airports and machinery. This urban noise typically occupies a low frequency band that can seep from urban and suburban areas out into rural and forested land.
Left: A map of the world’s shipping routes. Credit: National Center for Ecological Analysis and Synthesis.
In the ocean, shipping makes up the vast majority of constant added noise, but anthropogenic noises also include explosions, torpedoes, sonar, and deep water drilling. Explosives are the noisiest, typically around 304 dB, but a large ship’s engine generally emits noises around 192 dB. These ships make constant low frequency noise, in the 20-400Hz band. And in that low frequency band, the average ambient noise level in many places has been increasing.
Right: The tawny owl is a fair weather hooter. Credit: K.-M. Hansche.
Because there has always been noise, animals have always had some clever ways of dealing with it – but most of them were designed to deal with short-term noises like rain or wind. Many simply opt to wait until the noise stops. Tawny owls, for example, don’t bother calling when it’s raining. Bushcrickets, which usually call at night, will switch to daytime symphonies if there are other night-calling insects out there. Wrentits and Bewick’s wrens will alternate their calls, waiting for each other to finish. But unlike wind or rain, many human noises don’t go away. We’re remarkably good at being noisy all the time.
Left: Beluga whales are just one of the many species that exhibit the Lombard effect. Humans do too. Credit: Tony Fox.
So the next usual reaction to noise is to simply be louder. Humans do this too; you’ve probably come home from a party with a sore throat after yelling all night. Etienne Lombard first described this phenomenon in 1911, and since then the Lombard effect has been used to describe an increase in amplitude of a call or vocalization. The Lombard effect has been observed in zebra finches, Japanese quail, blue-throated hummingbirds, the common marmoset, beluga whales, orcas, manatees, humans and many other species.
But the Lombard effect is, again, only really useful for getting over short-term noisiness. It takes a lot of energy to yell all the time, and can strain the vocal chords or whatever other mechanism the animal is using to make sounds. It also makes it easier for predators and parasites to find you.
Right: Humpback whales have some of the most famous songs in the world, but they’re changing. Credit: Achim Raschka.
Some animals opt to simply call longer and more frequently. When exposed to low frequency sounds, humpback whales will increase the repetition in their phrases. Noise makes Japanese quail and King penguins repeat their calls over and over again. Orcas tend to elongate their signals. This too takes more energy, and could decrease the chance that the animals you are trying to reach will recognize you.
Left: The signature up-call of the right whale is almost impossible to hear through shipping noise. Credit: NOAA.
To get around yelling all the time, or calling longer, some animals gradually change the frequency of their calls. The North Atlantic right whale, for example usually sends its signals at low frequencies, from 40-400Hz. That’s the same region effected by shipping noise. (Try hearing the right whale’s characteristic up-call through all the traffic). So to get around it, the whales first increased the amplitude of its call to keep in touch with other whales during loud periods. Eventually though, the whales started calling at higher frequencies, to escape the shipping noise.
Changing the frequency of a call in response to urban noise was also observed recently in House finches. Past studies have seen similar reactions from blue monkeys and pygmy marmosets.
But there’s still a lot we don’t know about what our racket, and the changes these animals are making, will mean in the long run. Very few studies have been done on the costs of increased or changed signal production to the animals. We also don’t know what the upper limit of their vocal flexibility is – at what point is it just too noisy for them to communicate, and what happens when animals stop being able to compensate?
What we do know is that our sounds have an impact on animals. Many of them are doing the vocal equivalent of wandering around asking, "Can you hear me now?" And increasingly, the answer is no.
About the Author: Rose Eveleth is a graduate student in N.Y.U.’s Science, Health and Environmental Reporting Program. She’s currently trying to find someone to take her SCUBA diving in the Hudson River, and is obsessed with the sounds koalas make (seriously, listen). Really, she’s obsessed with sounds in general, so keep an eye out for her sound blog coming soon on Scienceline. (Photo: Rose Eleveth with a European Black snail. They don’t make any sounds, sadly)
The views expressed are those of the author and are not necessarily those of Scientific American.