Blue Whales Sing at Frequencies Killer Whales Simply Cannot Hear

A Song That Doubles as a Cloak

New research from the University of Washington finds some baleen whale species call at such deep frequencies that they're completely undetectable by killer whales, which cannot hear sounds below 100 hertz. The finding reframes what we thought we knew about one of nature's most dramatic predator-prey relationships — and it turns out the world's largest animal may have evolved one of the most elegant escape strategies in the ocean.

As researcher Trevor Branch put it, "the super-low, super-loud songs of flight species like blue and fin whales are the perfect tool: they can attract a female from hundreds of kilometers away, while being acoustically invisible to killer whales." In other words, the same call that carries across an entire ocean basin is, to an orca, essentially silence.

The Fight Club vs. the Flight Club

According to the fight-or-flight hypothesis, whales can be classified as "flight" species and "fight" species based on their response to approaching killer whales. "Flight" species are those that flee in the face of killer whale predation, such as blue whales, fin whales, sei whales, and minke whales. The "fight" species, by contrast, fight back in groups against predators. These include humpback whales, gray whales, bowhead whales, and right whales — larger, slower-moving animals that cluster near coastal areas and tend to sing at levels over 1,500 hertz, easily identifiable by killer whales.

Slow-moving, maneuverable "fight" species defend their calves in winter aggregations in predictable shallow coastal locations, while fast-swimming "flight" species flee on contact and typically disperse in winter across deep open waters. Male singing also differs between the two groups, with fight species producing more intricate songs to win group competitions, while flight species produce loud, monotonous songs to attract distant females. The division runs deeper than behavior — it appears to be encoded in the very sound of their voices.

How the Research Was Conducted

To conduct the study, Trevor Branch, professor of aquatic and fishery sciences at the UW, reviewed aquarium experiments on killer whales' hearing ranges, examined the source frequency and source level of populations of all baleen whales, and combined these with knowledge of how sounds move through the ocean to predict which whale populations can be easily heard by killer whales. Since killer whales cannot detect sounds below 100 Hz and can detect only loud tones below 1,500 Hz, singing at low frequencies results in acoustic crypsis. A review of baleen whale calling frequencies and source levels reveals that although all species are capable of acoustic crypsis, most fight populations produce calls above 1,500 Hz — unlike flight populations.

The ranges overlap on paper, but best sensitivity is not the same as any possible detection. A sound can technically fall inside an animal's broad hearing range and still be too low, too faint, or too masked by background noise to be useful at distance. That distinction is where the one-kilometre finding matters. That does not mean a killer whale can never detect a blue whale — orcas find prey through sight, movement, group hunting, learned routes, and their own sophisticated sound production.

What This Means for Understanding Ocean Life

"It just never occurred to me that some whales sing low to avoid killer whales, but the more I looked at this, the more I realized that every aspect of their behavior is influenced by the fear of predation," Branch said. That insight carries weight well beyond whale biology. It suggests that the acoustic environment of the ocean — every frequency, every decibel — has been shaped over millions of years by the pressure of predation.

Flight species with higher-frequency calls produced lower source-level calls, greatly reducing detection distances. Thus, flight species may call at low frequencies not only for long-distance communication but also to avoid detection by killer whales. As ocean noise pollution from shipping and sonar continues to grow in the very low-frequency range these whales depend on, understanding how their acoustic survival strategies work becomes not just scientifically fascinating — but urgently relevant to their conservation.