How do an­i­mals sleep stand­ing up?

World of Animals - - Animal Answers -

Horses have to lie down to en­ter deep sleep, but they can snooze stand­ing up so they’re ready to run if a preda­tor is de­tected. A se­ries of ten­dons and lig­a­ments in their legs work to­gether to ‘lock’ the joints and keep the horse bal­anced with lit­tle ef­fort. The sys­tem, called the stay ap­pa­ra­tus, en­gages when the an­i­mal re­laxes its mus­cles.

Flamin­gos are fa­mous for rest­ing while bal­anced on one leg. By study­ing dead flamin­gos, sci­en­tists found that a mus­cu­loskele­tal mech­a­nism works in a sim­i­lar way to the horse’s stay ap­pa­ra­tus and ‘snaps’ all the joints into place when one foot is placed di­rectly un­der the body and the other leg is folded away.

Sleep­ing like this is eas­ier than stand­ing on two legs and, as demon­strated by the fact that a dead bird will still bal­ance per­fectly, stay­ing up­right takes no ef­fort at all.

It’s eas­ier for a flamingo to sleep on one leg than bal­ance on two

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