The World Health Organization declared March 18 World Sleep Day. All living beings spend their lives in an alternating pattern of sleep and wakefulness. However, unlike people who are programmed to sleep at night, some animals can sleep during day time, some at night, while others try to stay awake as much as possible: so they are always on the alert.
Photo: a panda sleeping on a tree in the Wolong Panda Science & Research Center, Sichuan Province, China.
Mammals try to sleep in a position that allows maximum relaxation for their muscles; sometimes – like here – covering their head with paws. Photo: koalas in the San Diego Zoo.
After bathing, polar bears need to dry off and take a nap. Photo: a polar bear in the Berlin Zoo.
Even the heavy rain cannot rouse this sun bear in the Berlin Zoo from a sound slumber
Adult cats can sleep up to 16 hours a day. Domestic cats tend to sleep more than strays.
Cats can be overcomed by sudden attacks of drowsiness brought on by, for example, warm weather.
A sound asleep dog can quickly wakes up when it hears someone approaching the front door or other dogs barking.
Wolves sleep like dogs, curled up into a ball.
Although seals spend weeks at sea, they still enjoy relaxing on the shore: sleeping in the sun.
Gorillas sleep in the most spontaneous positions: lying on their back, face down, on their side; some sleep with their back against a tree or on tree branches.
Chimpanzees, gorillas, and orangutans sleep at least 10 hours a day. Photo: a monkey sleeping by a statue of Buddha in a temple, Kathmandu.
A Meishan piglet bred in China fast asleep among other pigs in the Berlin Zoo.
Horses usually sleep lying down for no more than two or three hours at a time. They doze while standing the rest of the time. They can even dream (when in REM sleep mode) when they are standing and dozing, but they always lie down to fully relax their muscles and have a good rest.
Source : http://en.rian.ru