Walrus Can Sleep Anywhere or Barely At All

March 10, 2009 -- 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.

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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.