JOAN CARTAN-HANSEN, HOST: Adult humans need about eight hours of sleep, and so do bunnies Like my pet rabbit Smokey.

But while I sleep at night, Smokey tends to sleep in shorter naps during the day.

Animals have different sleep habits from humans.

So, let's go to ZooBoise and see who sleeps when.

(Science Trek music) HARRY PEACHEY: For the most part, the phenomena of sleep-in animals is considerably different than it is in people.

CARTAN-HANSEN: Harry Peachey is the general curator at ZooBoise.

He and his staff take care of over 300 animals.

He says when humans sleep, we generally don't worry about someone trying to eat us.

PEACHEY: For a lot of animals, that's not the case, and they will grab their deep sleep in very, very brief segments, might even be a matter of seconds, because they always have to be prepared for the possibility that there is a predator lurking there that wants to take advantage of the fact that they are temporarily disabled by sleep.

CARTAN-HANSEN: Because of the possibility of predators, many animals have adapted their sleep patterns.

Giraffes sleep only about 30 minutes a day.

Cows sleep three to four hours a day, but usually in naps of one to five minutes at a time.

So, are there any animals that sleep like humans?

Well, baboons are primates like humans, and like us, they tend to sleep at night.

PEACHEY: But it's going to be the job of somebody in that group to be on the alert, to be on the lookout for predators, because there are species that prey on baboons.

And there will be a couple of individuals in the group that will be up high.

And because they're up high, they're going be sleeping lightly.

They're not going be in a deep sleep.

But if anything occurs around them that is a signal that there may be impending danger, they can see it right away.

CARTAN-HANSEN: When animals sleep is just as important as how long.

Scientists have classified animal sleep patterns into three groups.

PEACHEY: Animals that sleep at night when we are asleep are diurnal.

Animals that sleep in the morning and again at twilight are crepuscular, and then animals who are awake at night are nocturnal.

And these things work together to create functioning ecosystems.

For example, a good way to avoid a predator if you are a prey species is to sleep when they sleep, not when they're awake, because that makes you that much more vulnerable.

By the same token, there are predators that will adapt to a nocturnal lifestyle because a lot of the things that they like to eat are going be asleep and consequently more vulnerable at that time.

CARTAN-HANSEN: So the food supply is a big driver of when creatures sleep.

African wild dogs sleep on and off during the day.

They're classified as crepuscular because they are most active during the early morning and evening.

Tigers, on the other hand, are a bit more flexible.

They like to hunt in the early mornings and evening but are known to hunt at night.

PEACHEY: You know, everybody realizes that tigers are orange with black stripes.

And those black stripes help them hide in tall reeds or grasses and get closer to their prey.

The darker it is, the more effective that camouflage is.

CARTAN-HANSEN: Lions also tend to sleep during the day and hunt at night.

Their eyes have adapted to see better in the dark.

And that helps them find prey.

PEACHEY: Lions for example, um, may only successfully hunt every two or three days and eat six or 70 pounds of beef when they do.

When it's time to digest after they've had a big meal.

And this is something that they share in common with us.

And I think everybody, you realizes this Thanksgiving eve, you have a big meal, you need time to digest and sleeping may be part of that process, and if fact, your digestive processes do kick into gear at a new level when you're sleeping.

CARTAN-HANSEN: The animals we've talked about so far are all mammals, but insects sleep too, usually based on when they need to eat.

Birds sleep and mostly at night.

They need to daylight to see to fly But some, like owls, hunt at night and sleep during the day.

And then there's reptiles.

PEACHEY: Reptiles will, uh, be most active during the day and that has a lot to do with the fact that, um, their ability to regulate body temperature is somewhat limited.

So, they're dependent on ambient condition to warm up and they have to warm up in order to be active.

So they're kind of restricted to the daytime.

CARTAN-HANSEN: So, why do we all sleep?

Scientists think sleep may play some similar roles in humans and other animals.

Sleep is time for rest and healing.

Sleep is when chemicals in the brain and body realign.

But we don't know everything about animals and sleep including one big question: Do animals dream?

PEACHEY: Physiologists can monitor the brain patterns of an animal when they sleep, and they've done that with a number of species in particular primates.

But that doesn't mean that that animal is dreaming, it just means that the brain is active.

And there are, uh, REM, rapid eye movements that occur in other spaces.

Whether or not it's associated with dreams is hard to say.

By the same token, I would bet a dollar that every person that has a dog has looked at their dog sleeping on the floor and swore that dog is dreaming CARTAN-HANSEN: There is one big difference between humans and animals when it comes to sleep.

PEACHEY: Animals don't intentionally deprive themselves of sleep.

You know, we have work to do, we've got to study for a test.

And when you think about it, staying up late to study for a test so you can get that extra, extra hour and a half in of studying is going be to your detriment.

Because sleeping enhances our ability to, to consider things intellectually.

It enhances our ability to be creative.

So when we take that approach, we are compromising ourselves.

We compromise ourselves physically.

We compromise ourselves intellectually.

We compromise ourselves psychologically when we deprive ourselves of sleep.

CARTAN-HANSEN: So, learn something from the animals, and get to sleep!

If you want to learn more about sleep check out the Science Trek website.

You'll find it at ScienceTrek dot org.

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