Some baleen whale species are capable of evading orcas — their only known predators — by using stealth-like communication, according to new research.
Specifically, the marine mammals can sing at extremely deep frequencies that are “completely undetectable” to orcas, according to a study published on Jan. 31 in the journal Marine Mammal Science.
“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,” Trevor Branch, a professor at the University of Washington and study author, said in a university news release.
Only one group of baleens typically employs this type of covert communication, though. They are known as flight species, which flee when attacked, as their name suggests. They include blue, sei, fin, minke and Bryde’s whales.
These whales — which are usually found in the open ocean — are distinguished by their slender, streamlined bodies, which are adapted for quick movement.
Like all whales, they use singing as a way to attract mates, with males producing simple songs over long periods in order for females to locate them.
“But these super loud songs could expose them and their mates to killer whale attack,” Branch said in the release. “And this is where acoustic crypsis (a type of enigmatic behavior for avoiding predators) comes in: singing at low frequencies that are impossible, or very difficult, for killer whales to hear.”
By analyzing killer whale hearing ranges, he determined that the apex predators — which cannot detect sounds below 100 hertz — generally cannot hear the songs of flight species produced more than half a mile away.
In contrast, fight species — which stand their ground when attacked and include humpback, grey and bowhead whales — sing at higher frequencies, often over 1,500 hertz, which can easily be detected by killer whales.
These species, which are bulkier and slower, are typically found closer to coastlines, which can provide “easier defense against killer whale attacks—especially for group defense in aggregations,” according to the release.
There are pros and cons associated with both groups, with flight species being better able to avoid attack, but also having a harder time finding mates since they are dispersed in the open ocean.
“The research shows that under the sea there is a sound landscape governed by fear, with some whale species choosing to sing their songs to their prospective Valentines at deep levels to avoid attacks; while other whale species compete to sing the most varied and interesting songs, and fight back when attacked,” the release said.
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