Antarctic penguins don't sleep only at night

Antarctic penguins don't sleep only at night, but do so throughout the day - with 10,000 micro-naps a day. Each lasts only four seconds, and by the end of the day, they accumulate the necessary 10-11 hours. This mechanism developed in response to constant threats from predators: moreover, their brain can fall asleep with both hemispheres at once, or by turning off just one so that the other remains vigilant. And during these seconds, penguins don't just doze, but enter a real slow-wave sleep - the kind that the brain needs to rest.