The Big Sleep

This post belongs to a series of posts exploring the sleep habits of animals.

Dolphins, like humans, spend one third of their lives sleeping, as it has been observed that they spend 8 hours a day recharging their batteries.

Dolphins have different sleep behaviour from sharks and other fish, due to the fact that they are mammals. Indeed, dolphins cannot breathe under water and they usually hit the surface every 1-2 minutes to get their air -they can hold breathe for 7 minutes only in emergency! Therefore, dolphins cannot completely fall asleep under water, otherwise they would suffocate. They need to come back to the surface.

How do they do it? Like us, dolphins have a two-sided brain. They are able to “shut” one half of it at a time, allowing it to sleep. They close one eye and that side of the brain rests. This is how they get their mental rest.

In the meantime, the physical activity is greatly reduced as the dolphin moves very little. According to their preferences, dolphins have 3 usual resting behaviours that allow them to get their air (source: dolphinear.com):

• They swim slowly and hit the surface for air
• They rest at the surface with their blowhole exposed
• In shallow waters, they rest on the bottom and rise to the surface to breathe

This is how they remain strong swimmers (they can swim between 40 and 60 kilometers per hour) and maintain the use of their brain (20% larger that humans).

Sources:
http://www.dolphinear.com/data/dolphins.htm
http://web.mit.edu/seagrant/edu/res/dolphinsleep/question...
http://www.ri.net/RIGeo/rigea/earthwatch/earthwatch02/que...