Today I found out that dolphins don’t breathe automatically, rather it is always consciously done.

An interesting consequence of the fact that they need to be conscious to control their breathing is that they can never be truly unconscious, even when they sleep.  However, being mammals, their brains do need to enter a type of unconscious state every now and again in order to continue to function properly.

How dolphins handle this is to put one half of their brain to sleep, while the other half is still conscious and functioning.  They then alternate which side is sleeping periodically.  They stay in this state for approximately eight hours a day.  Doing this allows them to be conscious enough to control their breathing and periodically swim to the surface and get air, while still giving their brain the rest it needs.

Bonus Facts:

• Dolphins use not only their eyesight,  but also echolocation (similar to sonar) to avoid obstacles and find prey.
• The name “dolphin” comes from the ancient Greek “delphis”, which means more or less “fish with a womb”.
• Dolphins have been observed to teach their young to use tools.  They also have been observed to display a variety of cultural characteristics such as holding a type of funeral ceremony for their dead.
• Dolphins have no sense of smell due to lacking any olfactory nerve and lobes.  They use their sense of taste much like we use our sense of smell though.  Dolphins will often taste the water around them for this purpose.
• The ancient Romans once used dolphins to help them fish.  The dolphins were trained to drive fish towards fishermen.  Once a large enough group of fish was near the fisherman, the dolphins would signal the fishermen to cast their nets.   Today, this practice can still be observed in Santa Catarina, Brazil.
• Amazon river dolphins swim upside down.  It is thought that the humps on their backs help them feel around on the bottom of the river to locate food.  This also may help them see what is below them better as below their eyes they have puffy cheeks that obstruct their vision.
• Bottle nose dolphins and killer whales belong to the same family.
• Dolphins are the only animal other than humans that develop a natural form of type 2 Diabetes.
• Dolphins trained to kill by the Soviet Union were sold to Iran in the 1990s when the Russian military closed its marine mammal program.  The United States Navy still has such a program, though dolphins are supposedly not trained to kill, but rather to perform other tasks.