This female dolphin, named Say, was one of the sea mammals used in the experiments. She performed better, staying alert for longer than the male dolphin. (Brian Branstetter)

Okay, we’ve always known how smart dolphins are, but new research about their abilities is blowing our minds — or at least half our minds.

Scientists have discovered that dolphins sleep with only one half of their brains at a time. This allows them to stay alert for at least 15 days in a row. Researchers at the National Marine Mammal Foundation found that dolphins can identify objects in the water — including predators — and keep track of their environment for up to 15 days.

Dolphins probably developed the ability to sleep with only one half of their brain so that they could breathe at the surface of the water when half asleep, scientists say. This new research suggests that the need to be aware of dangers may also have helped dolphins develop this skill.

The researchers studied a male and female dolphin and found they could remain alert for five days. In fact, the female remained alert for 15 days. How much longer they could have continued was not studied.