Above the ice, Weddell seals communicate with the guttural cries of a Wookie, but research published in the journal Journal of the Acoustical Society of America has discovered that beneath the ice it’s a very different story. With an apparent affinity for the sound effects of Star Wars, microphones have recorded Weddell seals producing ultrasonic vocalizations fit for a George Lucas film, and researchers are baffled as to its purpose.
The unusual sounds produced by Weddell seals, Leptonychotes weddellii, were recorded using an underwater microphone called a hydrophone. The data collection period ran for two years at McMurdo Sound, Antarctica, following the installation of the McMurdo Oceanographic Observatory, where it’s said workers sometimes fell asleep while listening to the seals' soothing ultrasonic sounds. The recordings were analyzed by biologists from the University of Oregon (UO) who identified nine different types of tonal ultrasonic seal vocalizations reaching up to 50 kilohertz, around 20 kilohertz above sound detectable to the human ear.
If you think we’re exaggerating the likeness as an excuse to roll out as many references to the movie franchise as possible (Jar-Jar Binks was a Sith Lord btw) then check the sounds out for yourself in the video below.
As the world’s most southernmost-ranging mammal, Weddells are well adapted to life on the ice with teeth capable of carving out air holes so they can dive up to 600 meters into the near-freezing water in search of prey. They can cruise around for over an hour without coming up for air, so communication below the ice is likely as necessary as that up top.
"The Weddell seals' calls create an almost unbelievable, otherworldly soundscape under the ice," said the study's lead author Paul Cziko, a visiting research professor in the UO's Institute of Ecology and Evolution. "It really sounds like you're in the middle of a space battle in 'Star Wars,' laser beams and all."
It was thanks to the observatory's broadband digital hydrophone that the new form of vocalization was discovered. This recording equipment was superior to alternatives used in the past as it’s more sensitive and better able to detect higher-frequency vocalizations. As the researchers picked up on the ultrasonic call types in the data, they realized that the seals use these calls quite regularly. Elements including chirps, whistles and trills make up the other-worldly sounds, but exactly what they mean remains a mystery. And a mystery it is, as Weddells become the first pinnipeds to vocalize above the frequencies of audible sound.
"The possibility of seals using some kind of echolocation has really been discounted over the years," said Cziko. "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."
To date, there is no evidence for echolocation in Weddell seals, but the novel form of communication for the clade represents an exciting discovery made a short time ago in an observatory far, far away...