Despite all the hubbub over their hefty size, not much is known about blue whales' behavior in group settings, though they are not believed to be aggressive. "Very little is known about blue whale social structures. We do tend to see blue whales traveling alone or in small groups," says Ratner. "In terms of behavior in the wild, they don't tend to be very belligerent to each other or other animals, but rather focused on feeding or migrating, but again, behavior during breeding season could be very different and is still in need of more research." But marine biologists are studying one way that blue whales communicate with each other: sound.
"Blue whales produce one of the loudest sounds in the animal kingdom, a low rumble that can be heard hundreds of miles, and even reported to be thousands of miles away in the ocean," says Ratner. "Researchers are still unsure of the meaning of the vocalizations though, with best guesses being around finding mates or signaling opportunities for mating or feeding."
Jeff Jacobsen, a marine biologist with the Noyo Center for Marine Science, expands on the sounds of blue whales, which scientists use to estimate whale population size, among other factors. When these whale calls are repeated in a sequence, they become known as songs. Only male blue whales sing, however. "These songs differ by ocean basin, region. Their low frequency calls can be detected at very great distances, depending on ocean conditions," says Jacobsen in an email.
The frequency of their songs is affected by noisy conditions caused by objects like passing ships. Blue whales adjust the frequency of songs "by blowing air through their vocal cords at a faster or slower rate," according to a study which was conducted by a group of researchers at Oregon State University and published in August, 2017, after they observed a gradual decline in the frequency of blue whale calls. Scientists are still trying to figure out the meaning of these songs. Though since only males sing, these songs could be a factor in mating and courtship rituals.
If you're curious, you can listen to the sound of blue whales at Blue Whale Vocalization.