A new study on the sleeping habits of walruses reveals that these flippered marine mammals are some of the world's most unusual snoozers, since they appear to sleep anywhere, but they may also break the world's record for continuously staying awake.
Perhaps most unusual is their ability to sleep in various odd positions in the planet's ultimate waterbed — the ocean.
"In water, walruses slept while floating at the surface, lying on the bottom or standing and leaning," observed sleep expert Jerome Siegel and his colleagues.
Walruses may also catch some shuteye by literally hanging out, since the researchers say the blubbery animals have been seen "resting in water while using their tusks to hang from ice floes."
Siegel, director of the Center for Sleep Research at UCLA, and his team quietly viewed the behavior of Pacific female walruses previously caught in the Chukotka Sea and housed at the Utrish Marine Station of the Russian Academy of Sciences.
According to the study, which has been accepted for publication in the journal Behavioral Brain Research, each walrus had its own seawater pool and resting platform. All were healthy, adapted to captivity and were fed fish and squid three times a day. A younger walrus was fed a liquid soymilk and fish formula.
Siegel told Discovery News that when the walruses slept underwater, they could hold their breath for "about 4 to 5 minutes." Although the marine mammals experienced REM sleep while in water, it was fleeting. Any possible ocean-lulled dreams must be brief.
On land, the walruses settled into very deep sleep that could last for up to 19 hours. REM sleep was characterized by "visually detectable posture changes — the neck extended and the head moved forward and rested on the platform — muscle and vibrissae jerks as well as rapid eye movements."
Such a restful sleep was probably needed because the scientists determined walruses could engage in periods of almost continuous swimming for up to 84 hours. While other animals, including humans, can stay awake and active for this amount of time, to do this regularly and without forceful intention was previously unheard of.
"The discovery that walruses remain active for periods lasting up to 84 hours without showing behavioral signs of sleep is unprecedented," sleep specialist Niels Rattenborg told Discovery News.
"All other animals studied engage in at least some sleep every day," added Rattenborg, leader of the Sleep and Flight Group at the Max Planck Institute for Ornithology in Germany.
"If confirmed with recordings of brain activity, this finding will force sleep researchers to reevaluate many of their views about the regulation and function of sleep in general," he continued, mentioning that walruses occupy an "unusual ecological niche," part land and part sea, which could help to explain their surprising sleeping behaviors.
Siegel did find that walruses experience "unihemispheric sleep," where one half of the brain sleeps while the other stays active, but since the walruses swam continuously while in water — even making sharp turns — this still doesn't explain how they withstand such extended bouts of activity.
Walruses might break yet another sleep record: the greatest difference in total sleep time between individuals. That's because some walruses appear to be much bigger sleepyheads than others.
Although many successful people brag about dozing for only a few hours each night, sleep time actually varies little among humans in comparison to the more unpredictable snoozing habits of other animals, such as certain marine mammals, elephants and giraffes.