Dolphins can remain alert for up to 15 days at a time with no sign of fatigue

Oct 17, 2012
The female dolphin SAY who performed a continuous echolocation tasks for 15 days. Credit: Credit: Brian Branstetter

Dolphins sleep with only one half of their brains at a time, and according to new research published Oct. 17 in the open access journal PLOS ONE, this trait allows them to stay constantly alert for at least 15 days in a row. Brian Branstetter from the National Marine Mammal Foundation and colleagues found that dolphins can use echolocation with near-perfect accuracy continuously for up to 15 days, identifying targets and monitoring their environment.

The researchers studied 2 dolphins, one male and one female, and found that they were capable of this task with no signs of fatigue for 5 days. The female dolphin performed additional tasks for a 15-day period. How much longer they could have continued was not studied.

Sleeping with only one half of the brain at a time, or unihemispheric sleep, was believed to have evolved in dolphins to enable them to breathe at the surface of water even when half-asleep. This new research suggests that the need to remain vigilant may also have played a role in the evolution of this sleeping behavior.

"These majestic beasts are true unwavering sentinels of the sea. The demands of on air breathing dolphins have led to incredible capabilities, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behavior through echolocation" says Branstetter.

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More information: Branstetter BK, Finneran JJ, Fletcher EA, Weisman BC, Ridgway SH (2012) Dolphins Can Maintain Vigilant Behavior through Echolocation for 15 Days without Interruption or Cognitive Impairment. PLoS ONE 7(10): e47478. doi:10.1371/journal.pone.0047478

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User comments : 6

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3 / 5 (2) Oct 17, 2012
So dolphins are half asleep most of the time? No wonder they never took over the world. I wonder if unihemispheric sleep is typical of other cetaceans, such as whales. I wouldn't mind this ability myself, I think.
1 / 5 (6) Oct 18, 2012
That's awesome. But, they didn't really mention what happens after those 15 days and whether or not it's indefinite. It would be an amazing ability to have, but not entirely necessary in land-dwelling species.
1.6 / 5 (5) Oct 18, 2012
I still don't get this "sleep" thing. Evolution works on small advantages. There is nothing subtle about the disadvantages of being asleep.
Sleep should have been eliminated a long time ago, but here we are still sleeping.
I get tired just thinking about it.
3.7 / 5 (3) Oct 18, 2012
But, they didn't really mention what happens after those 15 days

Did you even read the article before commenting? It says quite plainly:
"How much longer they could have continued was not studied."

and whether or not it's indefinite

How would you test that?

There is nothing subtle about the disadvantages of being asleep.

There's also nothing subtle about the huge advantage of sleep. Low energy cost during a time of day (specifically for humans: night - and for some species also time of year (winter)) when your chances of getting food are virtually nil.

The brain requires roughly 20% of your energy. Shutting it down for a while frees up reserves for other things (immune system, healing, digestion, ... )

Efficient use of food is paramount for survival. And without survival (especially in lean times) you don't get to play in the evolutionary game for long.
1 / 5 (6) Oct 18, 2012
Did you even read the article before commenting? It says quite plainly: "How much longer they could have continued was not studied."

Yes, I read the article. But, given the vagueness of details related to the study, I assumed they were probably captive. And, if that's the case, you'd still think that after the 15 days, they would have noticed a slight change in behaviour, don'tcha think?

How would you test that?

Well, it's not necessarily testable, but one could make an estimated guess, based upon the fact that the animal never fully sleeps. At any given time, the dolphin is only partially asleep, so one could reasonably assume this would always be the case.
5 / 5 (1) Oct 18, 2012
Why don't you just read the article.

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