There are only so many hours in a day, and when that to-do list gets lengthy, you may find yourself wishing you could operate on less sleep. It turns out that elephant seals are living out that dream, sleeping a total of just two hours per day — much less than most mammals.
A new study published in the journal Science found that when foraging out at sea for months at a time, the animals split up their daily sleep into short naps, each usually under 20 minutes, and prefer to snooze deep underwater in order to avoid predators. “They’re able to hold their breath for a long time, so they can go into a deep slumber on these dives deep below the surface where it’s safe,” first author Jessica Kendall-Bar said in a press release.
She and her fellow researchers tracked eight wild northern elephant seals on foraging trips off the coast of California, which lasted around seven months and spanned more than 6,200 miles, the BBC reports. Each animal was affixed with a neoprene head cap that secured the same type of EEG sleep sensors used in human sleep studies.
The team found that the seals would dive at least 984 feet before falling into a deep sleep and gliding motionless through the water. Then, they’d transition to REM, or rapid eye movement, sleep, losing postural control of their bodies and drifting downward in a “sleep spiral,” during which they’d turn upside down and head farther into the blue. At such great depths, they’re unlikely to encounter predators.
“They look like falling leaves,” co-author Ritika Mukherji, of the University of Oxford, told the outlet.
Terrie Williams, a professor of ecology and evolutionary biology at UC Santa Cruz who worked on the study, added: “The thing I find remarkable is that any mammal would fall asleep while drifting hundreds of meters below the water surface.”
“This is not light sleep but real paralytic, deep sleep that would have humans snoring. Remarkably, the seal’s brain reliably wakes them out of it before running out of oxygen,” Williams explained.
The newfound data proves that elephant seals can live off as little sleep as actual elephants: African elephants currently hold the record for the shortest amount of slumber needed, at just two hours a day. But the seals’ behavior while foraging out at sea is a far cry from their sleeping habits during breeding season, when they typically spend up to 10 hours a day snoozing on the beach.