Yes, elephant societies are matriarchal. Yes, elephants are awesome.
The researchers used GPS trackers and “actiwatch implants” — basically, an animal Fitbit — to measure the creatures' activity levels. They found that both were polyphasic sleepers, meaning they napped in several short bouts over the course of a night. But those naps were few and far between; at one point, the elephants went 46 hours without resting. They traveled long distances during their sleepless periods, roaming as far as 19 miles, probably to escape predators or other disturbances. They only slept lying down every few days, and they dreamed just as infrequently.
Elephants in the zoo sleep for four to six hours a day, the scientists say. But, assuming the insomniacs in the study are representative of the rest of their kind, wild elephants' couple hours of shut-eye make them the most sleepless of any known land mammal.
That points to an interesting yet bewildering rule of biology, study author Paul Manger of the University of the Witwatersrand in South Africa told the BBC: The bigger an animal, the less it seems to sleep. Compare an elephant's short rest time to that of a North American opossum (18 hours a day), a cat (12 hours) or a pig (7.8 hours).
“Why this occurs, we're not really sure,” Manger said. “Sleep is one of those really unusual mysteries of biology, that along with eating and reproduction, it's one of the biological imperatives. We must sleep to survive.”
A review published in 2008 found no clear evidence of species that don't sleep, though not every animal rests in the same way. For example, dolphins — which need to be conscious to breathe — sleep by shutting half their brains down at a time. Even microbes exhibit circadian rhythms.
“Sleep is universal, tightly regulated and cannot be eliminated without deleterious consequences,” the authors of the 2008 review wrote.
Elephants' sleeplessness also calls into question the belief that rapid eye movement sleep (REM), when animals dream, is vital for memory consolidation. The female elephants in the latest study, who were both in their 30s, only exhibited REM sleep once every three to four days.
“Given the well-known memory of the elephant, this calls into question theories associating REM sleep with memory consolidation,” Manger said.