Sound behaves very differently underwater than it does in air — it travels roughly four times faster and, under the right conditions, loses far less energy over distance. Several whale species have evolved to make the most of this, turning the open ocean into a communication network that can span distances no land animal's voice could ever cover.

The SOFAR Channel: The Ocean's Natural Telephone Line

At a certain depth — roughly a thousand metres in many parts of the ocean — water pressure and temperature combine to create a layer where sound waves become effectively trapped, bending back into the layer rather than escaping upward or downward. This is known as the SOFAR (Sound Fixing and Ranging) channel. A low-frequency call that enters this layer can, in theory, travel for hundreds of kilometres with relatively little loss, which is part of why some large whale calls can be picked up on hydrophones an ocean basin away.

Humpback Songs vs. Blue and Fin Whale Calls

Not all whale sound serves the same purpose. Humpback whale "songs" are long, structured sequences of repeating phrases, typically produced by males during the breeding season, and they gradually change over the course of a season and from year to year as the whole population seems to adopt similar modifications — a rare example of vocal culture spreading through an entire species. Blue and fin whales, by contrast, tend to produce simpler, extremely low-frequency pulses thought to be used mainly for long-distance contact rather than elaborate composition.

A Few Categories of Whale Sound

  • Songs — long, repeating, structured sequences, best documented in humpback whales.
  • Social calls — shorter, more variable sounds used in everyday group contact.
  • Feeding calls — specific vocalisations some populations use to coordinate cooperative feeding behaviour.
  • Contact pulses — very low-frequency calls, especially in blue and fin whales, likely used to stay in touch over vast distances.

Why Songs Keep Changing

One of the more remarkable findings in whale research is how humpback songs evolve. Rather than staying fixed, a population's song shifts gradually, and those changes can spread across entire ocean regions as whales seem to pick up new phrases from one another — the closest known parallel to a cultural trend in a non-human species' vocal behaviour.

The Cost of a Noisier Ocean

Shipping traffic, sonar, and industrial activity have added a layer of low-frequency noise to much of the ocean that didn't exist a century ago, and it occupies some of the same frequency range many large whales rely on. Researchers studying underwater acoustics have raised concerns that this background noise can shrink the effective range over which whales can hear one another, effectively shrinking their world even though the ocean itself hasn't changed size. Reduced shipping speeds and quieter vessel designs are among the measures being explored to lower this impact.

The same physics that lets a whale's voice cross an ocean is completely different from what happens on land, where sound fades far faster. For a look at how sound behaves after dark instead of underwater, read about the acoustic world of nocturnal animals.