Male Sperm Whales Make the Loudest Communication Sound Ever Measured in Any Animal — and It Carries 70 Kilometers

Researchers at Aarhus University have measured what they say is the most powerful communication signal ever recorded from any animal: the slow, low-frequency clicks that mature male sperm whales fire off while alone in cold northern waters.

The clicks exceed 200 decibels re 1 microPascal (peak-to-peak) at the source. In good ocean conditions, the team estimates, a single click stays audible for about 70 kilometers — more than 40 miles. The findings were published in the Annals of the New York Academy of Sciences by lead author Simone K. A. Videsen, a postdoctoral researcher at Aarhus, and senior author Professor Peter Teglberg Madsen.

Sperm whales are already known for being loud. Their echolocation clicks, used to find squid a kilometer down in total darkness, are the loudest sounds any animal makes. But those are a sonar pulse, and the rapid coda patterns the animals exchange in social groups are something else again. These slow clicks are a third category, made almost exclusively by large solitary males, and they do not appear to be used for finding food.

The timing is what caught the researchers' attention. The clicks come at a rate of roughly 0.1 to 0.3 hertz — one every 5 to 10 seconds — and the intervals are held with what the team compared to "precision comparable to that of a drummer playing very, very slowly." Keeping metronomic time at that tempo is harder than doing it fast, and the regularity suggests the interval is carrying information rather than being incidental.

The anatomy behind the sound is extreme. A mature male's nasal complex can weigh more than five tonnes and takes up roughly a third of the animal's body length. The click is generated by structures called phonic lips, which in a big male are about the size of a car tire, snapping shut and sending a pressure pulse through the oil-filled organ that fills the front of the head. That organ works as an acoustic lens, focusing the pulse forward into a beam.

Why the animals do it remains open. The leading hypothesis is honest advertisement: the loudness and pacing of the click may be physically impossible to fake below a certain body size, making the signal a reliable broadcast of how big the sender is. That would fit a species where males compete for access to female groups scattered across enormous stretches of ocean, and where meeting a rival in person is expensive. But the researchers are explicit that the function has not been established.

The practical implication is about noise. A signal designed to work across 70 kilometers only works if the ocean is quiet enough to carry it. Shipping noise, concentrated in the same low frequencies, can compress that range from dozens of kilometers to a handful — which for an animal that may use these clicks to find mates across an ocean basin is not a marginal loss. The measurement gives researchers something they did not have before: a number for how much range is actually being taken away.