How Do Whales Communicate?

Sound travels roughly four and a half times faster in water than in air and loses energy far more slowly, while light is absorbed within tens of metres. For an animal spread across an ocean, sound is the only practical option.

Low frequency calls travel especially well. Fin and blue whale calls at around twenty hertz, near the bottom edge of human hearing, can carry across hundreds of kilometres, and in certain deep ocean sound channels considerably further.

Male humpbacks produce long structured songs made of repeated units arranged into phrases and themes, and a full song can last twenty minutes and be repeated for hours.

All the males in a population sing broadly the same song, and it changes gradually through the season with everyone adopting the changes. Occasionally a new song spreads across an entire ocean basin within a couple of years, which is one of the clearest cases of cultural transmission known outside humans.

Toothed whales including sperm whales, orcas and dolphins use clicks for echolocation, sending pulses and reading the returning echoes to build a picture of their surroundings and prey.

Sperm whales produce the loudest sounds of any animal, and they also use patterned click sequences called codas for social communication. Different sperm whale clans use distinct coda repertoires, which function rather like dialects and appear to be learned.

Bottlenose dolphins develop an individual whistle within the first year of life and use it throughout their lives. Other dolphins copy it when addressing or seeking that individual.

This is about as close to a name as anything documented in animals. Playback experiments show dolphins respond to their own signature whistle and not to others, and mothers and calves use them to reunite after separation.

Ocean noise from shipping, sonar and seismic surveys overlaps heavily with the frequencies whales use, and it has risen substantially over the last century.

The documented effects are significant:

• •Reduced range over which whales can hear each other
• •Changes in calling behaviour, including calling louder or falling silent
• •Displacement from feeding and breeding areas
• •Strandings linked in some cases to naval sonar

Since 1989, hydrophones have repeatedly detected a whale calling at around fifty two hertz, a frequency far higher than blue or fin whales use. It has been tracked across the North Pacific for decades.

The story spread widely as an account of an animal calling at a frequency none of its own kind can hear. Researchers are more cautious, noting that other whales can almost certainly hear the calls even if they do not use that frequency, and that the animal appears healthy and follows normal migration patterns. It may be a hybrid or simply an unusual individual.

Toothed whales and dolphins do not produce their clicks with a voice box in the way you speak. They push air past structures called phonic lips inside the nasal passages beneath the blowhole. The sound then passes through the melon, a rounded fatty organ in the forehead, which helps focus it into a beam. Returning echoes are picked up largely through the lower jaw, where fatty tissue channels vibrations towards the ear. This system lets them click repeatedly without releasing air into the water.

Baleen whales, such as humpbacks and blue whales, use the larynx instead, but with an important difference from land mammals. They can move air back and forth between the lungs and an air sac attached to the larynx, recycling the same air rather than losing it. Studying all this is difficult, because whales are large, fast and often far away. Researchers use underwater microphones called hydrophones, sometimes in arrays that pinpoint where a call came from, and suction-cup tags that record both the sounds and the movements of individual whales.

Whale song was not studied seriously until the second half of the twentieth century. Underwater microphones installed for military purposes during the Cold War picked up sounds that engineers sometimes could not explain. Recordings of humpbacks made off Bermuda by a US Navy engineer, Frank Watlington, reached the biologists Roger Payne and Scott McVay. Turning the sounds into printed spectrograms, they noticed that the long sequences repeated in a fixed order. In 1971 they published a paper in the journal Science describing the sounds as songs, a word chosen precisely because of that repeated structure.

The recordings also reached the public. An album of humpback songs released in 1970 sold widely and became a soundtrack for the campaign against commercial whaling, which was still killing very large numbers of whales each year. Humpback song was later included on the Golden Record carried by the two Voyager spacecraft launched in 1977, alongside human music and greetings. A worldwide moratorium on commercial whaling, agreed by the International Whaling Commission in 1982 and in force from the mid 1980s, followed years of campaigning in which the sound of whales played a surprisingly direct part.

Sound is the most useful channel in the sea, but anything that calls can be overheard. Killer whales in the coastal waters of the north-east Pacific show how this shapes behaviour. Fish-eating groups, which hunt salmon, call and click freely, since salmon hear poorly at the frequencies orcas use. Groups that hunt seals, sea lions and porpoises behave very differently. Their prey hear well, so these orcas travel and hunt mostly in silence, using echolocation sparingly. They often become noisy only after a kill, when there is no longer anything to give away.

Some whales may stay quiet to avoid becoming prey themselves. Beaked whales, which dive to great depths to hunt squid, echolocate intensively at depth but tend to fall silent in the upper part of the water column, where orcas hunt. They also tend to rise slowly and quietly from their deep dives. Researchers think this pattern reduces the chance of being detected by listening predators. It is a useful reminder that communication always has an audience, and that the decision not to make a sound can matter as much as any call.

Long-term recordings can reveal changes no single study could. When researchers compared blue whale songs recorded around the world since the 1960s, they found that the pitch of the songs has been falling steadily, in several separate populations at once. The cause is still debated. One idea links it to the recovery of whale numbers after commercial whaling ended: with more whales around, males may not need to call as loudly to be heard, and lower, quieter calls could carry enough. Other researchers have suggested links to ocean noise or changes in seawater, so the puzzle remains open.

An accident of history provided a rare test of how shipping noise affects whales. After the attacks in the United States on 11 September 2001, ship traffic in the Bay of Fundy in Canada dropped sharply for a few days. A research team happened to be studying endangered North Atlantic right whales there, collecting their floating faeces, partly with the help of trained detection dogs, to measure stress hormones. Underwater noise fell noticeably, and stress hormone levels in the whales were lower than in the same period of other years. The finding, published years later, linked everyday shipping noise to chronic stress in whales.

Whales communicate through low-frequency calls that travel for hundreds of kilometres, structured songs that spread culturally between populations, and click patterns that in some species act like dialects and even names.