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For the past two decades, scientists have documented a gradual lowering of the frequency of blue whale calls and they haven't been sure why – or even whether the phenomenon is intentional.
Other baleen whales in the North Pacific have been recorded in recent years generating vocalizations that are missing the "overtone" portions of their calls. Again, scientists are unsure why.
A new study published this week in Scientific Reports may shed some light on these mysteries. A group of acoustic researchers at Oregon State University's Hatfield Marine Science Center recorded a blue whale call, then created a model to replicate that sound based on a series of controlled air bursts from the animal's vocal cords.
In other words, they showed that whales can control the frequency of their calls by blowing air through their vocal cords at a faster or slower rate.
"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, an acoustics scientist with the National Oceanic and Atmospheric Administration and lead author on the study. "It was long thought that they generated their calls mostly by resonating sound in large chambers or cavities in their upper respiratory system.
"But this implies that the frequency of the whale's calls are dictated by the size of the animal – the lower the frequency, the bigger the animal. 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."
Read the full article at phys.org