Dolphins can remain alert for 15 days at a time, study finds

If you’re the type who keeps a case of Red Bull under their desk at work for those long nights, you have a new role model: The remarkable ability of dolphins to rest only half their brain at a time allows them to remain alert indefinitely, according to a study published Wednesday in the journal PLoS ONE.

Researchers believe that dolphins evolved this enviable sleeping ability because without it they would have a difficult time continuously breathing in the ocean. But, according to the new research, it also endowed them with the unique ability to never tune out at all.

In the study, researchers from the National Marine Mammal Foundation tested a male and a female dolphin in a research pen just off the coast of San Diego. The dolphins were required to use their sound-based navigation systems -- an ability called echolocation, which functions like a submarine’s sonar system -- to find targets randomly spread throughout the pen.

The dolphins were taught to bump a paddle at the end of the pen every time they thought they found a target; when they were correct, they received auditory feedback and some fish to eat.


The two dolphins became very good at the task. The female responded correctly over 90% of the time, and the male over 75% of the time. And, incredibly, as the experiment wore on -- three, four, five days straight -- their performance waned only slightly. In fact, the female dolphin was tested for 15 days straight with no apparent effect on performance.

The results suggest that breathing may not be the only reason dolphins evolved the ability to sleep one brain hemisphere at a time: Being continuously alert also probably allows dolphins to detect and flee their predators.

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