• Researchers found that Weddell seals actually produce sounds that people can't hear
  • The chirps and whistles they make sound rather like a battle in "Star Wars" 
  • Other pinnipeds are so far not known to vocalize in the ultrasonic range

The seals in Antarctica are apparently making more sounds than previously thought. It's just that people can't hear them.

For a new study, now published online in the Journal of the Acoustical Society of America, a team of researchers listened to two years' worth of recordings from the underwater observatory in McMurdo Sound in Antarctica and found that Weddell seals vocalize underwater at frequencies that are no longer audible to humans.

In total, the researchers captured nine high-pitched vocalizations including chirps and whistles that reach 50 kilohertz. As the news release from the University of Oregon (UO) explained, humans can only hear in the sonic range, which is up to 20 kilohertz.

"The Weddell seals' calls create an almost unbelievable, otherworldly soundscape under the ice," study lead author Paul Cziko said in the UO news release. "It really sounds like you're in the middle of a space battle in 'Star Wars,' laser beams and all."

Pinnipeds, which include seals, walruses and sea lions, were previously believed to produce sounds only at the sonic range, or the range that people can hear, the UO news release explained. No other pinnipeds are known to make ultrasonic vocalizations, therefore the researchers' findings make Weddell seals the only pinnipeds capable of such a thing. And as study co-author Lisa Munger explained in the UO news release, they use the ultrasonic calls "quite regularly."

Why they produce sounds at this range, however, is still unclear. In the news release from the McMurdo Oceanographic Observatory (MOO), Cziko offered several possible explanations for the ultrasonic vocalizations, including using it to communicate with other seals when the "lower frequencies are cluttered with other sounds," or perhaps for echolocation, much like dolphins do.

In fact, the UO news release noted that it is so far unknown how Weddell seals find prey and navigate during Antarctic winter when the conditions are nearly completely dark. It's possible then that these ultrasonic "Star Wars" sounds could be evidence of Weddell seals' echolocation.

"The possibility of seals using some kind of echolocation has really been discounted over the years," Cziko said in the UO news release. "We actually had a lot of somewhat heated discussions in our group about whether or how the seals use these ultrasonic sounds for echolocation-like behaviors."

As Cziko explained in the MOO news release, Weddell seals are known to be one of the "most vocal" among the seal species, with some areas in the under-ice soundscape in Antarctica already "dominated" by the audible sounds they make. The researchers' discovery shows that perhaps they are even more vocal than previously thought.

And no matter how they use their "Star Wars"-like vocalizations, the researchers' findings add to the all-important information about these incredible creatures.

Weddell Seal
Pictured: Representative image of a Weddell Seal at a breathing hole. Giuseppe Zibordi/Michael Van Woert, NOAA NESDIS, ORA/Wikimedia Commons/Public Domain