Or­cas start life by hit­ting snooze

World of Animals - - Animal Clocks -

Orca calves don’t sleep reg­u­larly for the first few months of their lives, begin­ning with an ex­tended pe­riod with­out a cir­ca­dian rhythm. Mothers even sus­pend their own bi­o­log­i­cal clocks for at least four weeks to keep a watch­ful eye on their pre­cious new baby. Killer whales and other dol­phin species have been ob­served to stay awake for up to 98 per cent of their baby’s ini­tial two months, while calves only slept for ten per cent of that time.

Adult dol­phins rest half of their brains at a time while the other half re­mains ac­tive enough to watch out for dan­ger. Or­cas do ex­pe­ri­ence cir­ca­dian rhythms de­spite not hav­ing a reg­u­lar 24-hour sleep-wake cy­cle. The adrenal glands pro­duce a hor­mone called cor­ti­sol that reg­u­lates blood pres­sure and in­flam­ma­tion and plays a huge role in the an­i­mal’s fight or flight in­stinct. This ac­tiv­ity is con­trolled by their in­ter­nal clock in the same way as a ter­res­trial mam­mal.

Orca calves mea­sure 2.6m (8.5ft) at birth andweigh in at around 120–160kg (265–353Ib)

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