Why Are Blue Whales Changing the Frequency of Their Songs?

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Blue whales are mysteriously changing the frequency of their calls. NOAA

Blue whales are the largest animal ever known to have existed, and they have some mighty calls that can be heard from up to 600 miles away. But researchers have been noticing something strange going on with these majestic sea beasts: Their songs seem to be mysteriously lowering in frequency over the last several years.

This is surprising because the frequency of their calls was previously believed to be fixed depending on the size of the animal. That's because they use massive chambers in their respiratory system to generate sounds, and the size of the chamber ought to determine the frequency of sound that resonates from it. But if their calls are universally getting lower without any reason to believe the animals are also uniformly changing sizes, something else must be going on.

Previously, researchers believed that whales were changing their tune in reaction to the increasing amount of human noise in ocean waters caused by ships, submarines and deep sea exploration. However, a new study shows that climate change and warmer waters could also be to blame.

A team of international scientists and researchers analyzed more than 1 million songs recorded from 2010 to 2015 from three species of blue whales (fin, Antarctic blue and pygmy blue whales) in the southern Indian Ocean. They discovered that the whales would change their pitch during the same seasons when massive sea ice shelves would crack and break apart — meaning the whales were trying to have their sounds heard above the roaring noise of breaking ice.

While the notion that melting ice affecting whales seems detrimental for both the animals and climate change, there is one positive note the study addresses. Over the last several years, the number of ships in the southern Indian Ocean has decreased while the population of blue whales has increased. Scientists believe the whales could also be changing their pitch because their sounds don't have to travel as far to reach one another.

While nature appears to be a factor in how whales are evolving and adapting, mankind still has to take some blame.

Humans play a role, too

In 2017, a team of acoustic researchers from Oregon State University's Hatfield Marine Science Center recorded a blue whale call to study what was affecting the animal's vocalizations and how it adapted to change, reported Phys.org.

"Our study shows that blue whales in particular – and perhaps other baleen whales in general – may be making their harmonious sounds in a much different way than previously thought," said Robert Dziak, lead author on the study.

Dziak and colleagues were therefore prompted to look for another factor in how these enormous creatures generate their calls. So, they created a model that replicates the types of sounds that blue whales make, and found that by toggling the rate at which air is passed over the vocal cords, the calls could be more accurately mimicked. It's an entirely new way of thinking about whale songs.

"We show that blue whales can make these low frequency sounds, and even change frequency in the middle of their call, by pulsing air through their vocal cords," explained Dziak.

This also implies that the frequency by which blue whales communicate could be determined by a choice made by the animals themselves. But why would blue whales everywhere be collectively choosing to lower their call frequency? A number of theories have been forwarded, but scientists suspect it might have something to do with increasing noise in the ocean caused by human activity.

"We conducted a year-long study of sound off the Oregon Coast and at times it can be really noisy out there," said Joe Haxel, an Oregon State University acoustics specialist. "In addition to vibrant natural sounds – especially waves breaking on the beach – a few long-term studies have documented a substantial increase in ocean noise over several decades from expanding container shipping traffic.

"It may be possible the whales are modulating their vocalization frequency in response to an increase in human-generated noise. They are essentially trying to find a radio channel that has less static to communicate in."

If this is indeed what the whales are doing, it's a remarkable adaptation, but also an alarming one. We are only beginning to understand how human-generated sounds impact ocean ecosystems. Whales might have the ability to adapt-- at least to a point-- but that might not be the case for so many other ocean critters that also communicate via sound.