Do animals have the same sleep requirements as humans?

This week's question comes from Tom Byerley in Ottawa. He asks: "We are told that to function at our best we need to have a certain number of hours of sleep each day. Does the same rule apply to other, or even all members of the animal kingdom?"

Dr. Mary McNiven, a professor of animal science at the Atlantic Veterinary College in Charlottetown, says all animals have sleep requirements. They don't get, or even need the eight hours a day that we do, they may not even require daily sleep, but they still require a little shut-eye at some point.

The amount varies depending on the particular species. Risk of predation is also a factor. For example, elephants and giraffes only require a few hours a day, because they have to be so vigilant about predators. This also explains why baby orcas, as well as their mothers, do not sleep for the first month of their lives. It is the period when they are most vulnerable.

Horses really do nap standing up, but in order to get the necessary amount of REM sleep, they will eventually lie down, but only for short periods of time. Cows sleep, but in a state known as 'drowsing', which is a combination of being asleep and awake. Migratory birds do not sleep en route, but like many other species, if they become sleep deprived, they will make up the missing requirement over a longer period of time.