A blue whale pod [Photo by Flip Nicklin, Minden Pictures]
The past two decades have seen the calls of blue whales gradually get lower and lower in frequency. Recordings also show that other North Pacific baleen whales are also generating calls that don't include an “overtone”. Scientists have been unsure why these things have been happening, but it's possible that human activity is to blame.
These findings are surprising to scientists, who have thought that the frequency of whale calls are fixed based on the size of the whale. Chambers in their respiratory systems produce the sounds, and the size of these chambers determine the frequency of whale calls. The larger the animal, the lower the frequency of the calls it emits. Since it's unlikely that the whales are changing sizes, leading them to change the frequency of their calls, there may be something else afoot.
Scientists are also suggesting that whales may be changing the frequency of their calls on purpose.
Photo by Mike Baird
There are a number of human activities that can potentially affect whales in the ocean. For the purposes of this subject, however, let's look at two: commercial whaling and noise from ships. According to a new study, these two are both possible reasons for the changes whale calls. However, the noise at sea may be the reason why whales are changing the frequency of their calls.
Acoustic researchers at Oregon State University conducted a year-long study off the Oregon coast and discovered how noisy it can be out there. There are already a plethora of natural sounds out at sea—the sound of waves breaking, for example—but the sound of container ships add to the cacophony.
“It may be possible the whales are modulating their vocalization frequency in response to an increase in human-generated noise,” says acoustics specialist Joe Haskel, one of the researchers. “They are essentially trying to find a radio channel that has less static to communicate in.”
Researchers came up with a model that can replicate the sounds that blue whales make to see how the whales are making sounds at a lower frequency. The researchers then toggled the rate at which air passes through the vocal cords and were able to more accurately mimic the frequency at which whales make their calls now.
It's getting noisy out at sea.
Thus, the study shows that the whales can change the frequency of their calls, even right in the midst of them, by changing the rate at which they let air pass through their vocal cords. It's also possible that the whales are making a conscious choice to change the frequency of their calls, perhaps to deal with noise pollution at sea.
What we may be seeing, therefore, is adaptation almost in real time. If the blue whales are indeed changing their frequency to adapt to human-generated noise pollution, then it's remarkable. However, this also means that we're generating so much noise at sea that we're forcing whales to make such a significant change in themselves. Whales may be be able to adapt to these changes, at least for now, but other sea animals might not be as lucky.
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