New findings reveal that certain baleen whale species produce calls at such low frequencies that killer whales cannot detect them, since these predators can’t hear sounds lower than 100 hertz. Interestingly, these same baleen whales often choose to flee when attacked by killer whales.
Killer whales are the sole natural enemies of baleen whales, which have special structures called “baleen” that help them filter plankton from the water. Unlike toothed whales that tend to be more social, baleen whales are often solitary and are vulnerable to attacks, particularly in mother and calf pairs. Some baleen whale species may fight back during an attack, while others prefer to escape.
Despite their vulnerability, whale species are known for their loud underwater vocalizations. So, how do killer whales avoid targeting them based on these calls?
Research from the University of Washington has found that certain baleen whales communicate at frequencies low enough to be inaudible to killer whales. These species, which include blue, fin, sei, Bryde’s, and minke whales, are usually the ones that opt for flight in the event of an attack.
Conversely, the baleen whale species that engage in combat when attacked—such as right, bowhead, gray, and humpback whales—tend to produce higher-frequency calls. These fighting species are also generally slower and more agile.
This research was published on January 31 in Marine Mammal Science.
In this study, Trevor Branch, a professor at the UW’s School of Aquatic and Fishery Sciences, reviewed existing experiments regarding the hearing abilities of killer whales, assessed the frequency and volume of sounds produced by different baleen whale populations, and integrated this information with knowledge on sound propagation in the ocean to determine which whale populations are likely to be heard by killer whales. The findings indicate that the calls of fleeing species can usually only be heard by killer whales from distances of less than one kilometer, which is significantly shorter than the range for the fighting species.
The concept of “fight or flight” is not new; however, insights from this acoustic research reveal new dimensions about the adaptations of baleen whales. Is it possible that this “acoustic crypsis,” where whales communicate at low frequencies that remain unnoticed by killer whales, has evolved as a survival mechanism against attacks?
Killer whales inhabit all oceans and have a varied diet that ranges from small fish to the largest whales in existence. The baleen whales that engage in fights usually migrate and give birth in shallower coastal waters, creating a safer environment that offers better defense against killer whale attacks, particularly in groups. Their slower swim speeds and adaptability make their higher-frequency vocalizations, which exceed 1,500 hertz, easily detectable by killer whales. In contrast, the fleeing species tend to have slender, hydrodynamic bodies suited for speed and often occupy broader, open ocean areas for breeding and birthing, allowing them to escape in multiple directions.
These behavioral traits significantly impact their feeding and mating strategies. The densely populated shallow coastal areas may provide less food for the fighting species, while the open ocean preferred by fleeing species offers richer resources. However, finding a mate is easier in closely congregated locations than when individuals are dispersed over vast distances.
Vocalizations play a crucial role in attracting and selecting mates among whales. Males from fleeing species craft their songs to reach as many females as possible, often using simple and repetitive patterns, and singing for extended durations so females can locate them.
“However, these loud songs might also expose them to killer whale attacks. This is where acoustic crypsis plays a role: singing at low frequencies that killer whales find difficult or impossible to perceive,” Branch explained.
The research suggests that the underwater soundscape is shaped by fear, prompting some whale species to serenade their mates at deep frequencies to evade predators, while others compete with each other through complex and engaging songs and resist attacks. The distinctions between the fighting and fleeing behaviors seem to influence every aspect of baleen whale life, including their habitat, communication methods, and breeding and feeding strategies.
“I never realized that some whales sing at lower frequencies to avoid killer whales, but the more I studied this, the clearer it became that the fear of predation affects their behaviors across the board,” Branch noted.
