Dolphins Can Sleep With Only Half Their Brain at a Time

Posted on October 18, 2012

Dolphin Named SAY


A new study has found that dolphins sleep with only half of their brains at a time. This enables them to stay constantly alert for at least 15 days in a row. The research study was published here in PLoS One.

Brian Branstetter from the National Marine Mammal Foundation and his 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 two dolphins, one male and one female. They found the dolphins could use echolocation with no signs of fatigue for five days. The female dolphin, named SAY (pictured above), performed additional tasks for a total of 15 days. The researchers did not continue the study after 15 days, so it is likely she could have gone much longer.

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

The researchers say that sleeping with only one half of the brain at a time (unihemispheric sleep) is believed to have evolved in dolphins to enable them to breathe at the surface of water even when they are half-asleep. The scientists say the new researchers indicates a need to remain vigilant may also have played a role in the evolution of dolphin sleeping behavior.

Photo: Brian Branstetter