Some baleen whales whisper at frequencies inaudible to killer whales, using acoustic crypsis as a survival strategy to avoid predation.
Acoustic crypsis is a behavioural adaptation that helps animals avoid being detected by predators that eavesdrop on their sounds.
Recent research has revealed that certain baleen whales, including blue, fin, sei, Bryde’s, and minke whales, communicate at frequencies below 100 hertz, rendering their calls inaudible to killer whales. This behaviour, known as acoustic crypsis, is believed to be a survival strategy to avoid detection by orcas, their main predators.
A distinct pattern among whale species
Not all baleen whales rely on whispering. Right, bowhead, grey and humpback whales produce higher-frequency sounds that fall within the auditory range of killer whales. Instead of avoiding detection, these species tend to confront orcas rather than flee, suggesting a difference in anti-predator strategies.
The fight-or-flight response
The study, published in Marine Mammal Science, highlights a clear divide in how baleen whales react to predation threats. Species that whisper are more likely to flee upon detecting killer whales, while those that produce louder, higher-frequency sounds are more likely to defend themselves.
Energetic costs and adaptations
Additional research published in the Royal Society’s Biology Letters suggests that acoustic crypsis may also be influenced by energy efficiency. Producing lower-frequency sounds requires less energy than high-frequency calls, which may be an added advantage for large whales undertaking long migrations. This dual benefit—avoiding predators while conserving energy—could explain why acoustic crypsis has evolved in certain species.
Implications for marine research
This discovery sheds light on the evolution of whale communication and how predator-prey dynamics shape marine ecosystems. Further acoustic monitoring could reveal more about how whales adapt their vocal behaviour to changing ocean environments and increasing human-generated noise pollution.
Fact file
Acoustic crypsis is a behavioural adaptation that reduces detection by eavesdroppers, including predators. This approach to reducing conspicuousness is beneficial for species that rely primarily on acoustic signals for communication.
Examples of Acoustic Crypsis:
Reduced calling rates: Some animals decrease the frequency of their calls or vocalisations in areas or times when predation risk is higher.
Lower amplitude calls: Animals might produce weaker calls or sounds, reducing their audibility at a distance.
Habitat selection: Certain species might prefer habitats or locations that naturally limit the range or clarity of their calls, making it harder for predators to hear them.
Vocalisations that resemble background noise: Some animals may adapt their vocalisations to blend in better with environmental sounds, making them difficult to distinguish.
