Ecology
Dolphins can stay awake for more than two weeks with only half of their brains asleep, scientists have found.
The study showed that dolphins can thus constantly watch sharks. Unlike terrestrial mammals, dolphins only sleep half of their brains at any given time. Half of their brain is resting, while the other is on alert, and they are constantly changing their active side.
“After being awake continuously for hours and days, humans and other animals are forced to stop all activity and fall asleep,” explained Brian Branstetter, marine biologist at the U.S. National Marine Mammal Foundation in San Diego. “Dolphins don't have such restrictions, and if they did, they would likely drown or become easy prey.”
To ensure dolphins' vigilance, scientists tested their ability to scan the environment. Dolphins use echolocation to get an idea of the world, a biological form of sound location where they “whistle” and listen to echoes to explore the environment.
Scientists have found that these animals can use echolocation continuously for 15 days. In the study, two dolphins were tasked with scanning special modules using echolocation. Dolphins may be able to stay awake much longer, but researchers haven't tested further.
“Dolphins can continue to swim and think for days without rest or sleep, maybe even indefinitely,” the scientists explained.
Dolphins developed the ability to sleep with only half of their brains so they could breathe on the water surface even when they were half asleep. The need to stay alert also played a role.