National Geographic On Assignment
The sperm whale belts out the loudest sounds in the animal kingdombooming clicks, quite different from the tonal songs of the humpback whales, which can carry up to six miles (ten kilometers) through the depths.
Sperm whales use different types of clicks for communication and for finding food. The loudest of the clicks work like biosonar to help identify squid and fish, anything from sardines to sharks.
These clicks can measure about 230 decibels underwater, equivalent to 170 decibels on land"about as loud as a rifle shot three feet from your ear," said Magnus Wahlberg of Aarhus University in Denmark, a biologist and a co-leader of the sometimes frightening quest to listen in on the whales.
Wahlberg and his colleagues have found a way to use the clicks to gauge the size and possibly the age of the whales, teasing data from a population largely hidden from human eyes. The new research may also help reveal whether human noise pollution from sources like military and civilian sonar might affect the whales.
Not until the 1950s did scientists associate the big clicks with sperm whales.
"People heard all these knocking sounds but had no idea that these came from one of the biggest mammals on Earth," said Wahlberg. "There was no easy way to connect the sounds with what was down there."
As big as the sounds are, their intensity is difficult to measure. "[They're] emitted in a narrow beam like a flashlight, and you have to be directly in front of the animal to measure the full magnitude of the sound," said Wahlberg. "You have to listen for a long time and be very lucky."
From Clicks to Size
The team's research has conclusively established that sperm whales are indeed the loudest creatures on Earth.
The clicks are made up of sound pulses reflected between air sacs within the whales' nose, which can grow to about 15 feet (4.5 meters) long. Researchers can use the interval between pulses to calculate the length of the whale's nose, from which they derive the whale's length.
The theory behind the technique dates from the 1970s. In 1991, Jonathan Gordon, a zoologist with the University of St. Andrews, in Scotland, developed the equation to calculate length from click size.
But nobody knew whether the technique was accurate.
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