Humpback whales sleep upside down.

Humpback whales breathe voluntarily, unlike human beings.
Since they have to remember to breathe, researchers believe humpback whales sleep in short 15 to 30 minute naps between breaths.

While resting, it is believed that these whales put half their brain to sleep, the other half is able to watch for predators, control their position in the water and care for their young, which float close to them.
This is common for many marine mammals, from whales to dolphins, which all have to be conscious breathers to survive underwater.

During these stationary periods, humpback whales often hang in an upside down, head-down, tail-up position, approximately 15-30 meters below the surface.
Male humpbacks have also been found in this position singing their famous songs. The singing whale will maintain this position until it surfaces to breathe, and then immediately resumes the upside down position after diving.
A song typically lasts 8-15 minutes (although it may range from 5-30 minutes), and then is repeated over and over in a song session that may last several hours.

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