(Sound of LUKAS blowing raspberries)
I'm standing next to Dr. Kristen Lukas at Cleveland Metroparks Zoo; she's blowing raspberries and impersonating her favorite animal, the gorilla. Lukas is curator in the conservation and science division at the zoo. The gorilla? That's Beeback, arising from an afternoon siesta.
(Sounds of Beeback pounding his chest)
LUKAS: That was really cool. That’s the thing about animals - when they feel like pounding their chest, they do. And when they feel drowsy, they don’t fight sleep like humans often do. They give in. Maybe that’s why animals often look so much more rested than us humans.
The variation in animal sleep fascinates Grace Fuller, a biology graduate student at Case Western Reserve University and colleague of Lukas’ at the zoo.
FULLER: We have a hairy armadillo who tends to sleep on his back with his little legs up in the air twitching.
Fuller’s demonstrating, with her arms scrabbling at the air.
FULLER: And it looks like he’s having little armadillo dreams or something. That’s very anthropomorphic but you sort of wonder what’s going on there, with his little legs up in the air.
Scientists don’t know if animals dream. If fact, they know little about why exactly sleep is necessary - just that it is and that all animals do it. And mammals, in particular - warm-blooded creatures with backbones - share the same fundamental sleep cycle. Fuller explains.
FULLER: We see pretty much four stages of sleep in humans and other mammals and you call it the sleep architecture and it looks quite similar between us and other mammals. When you look at a fish or something like that, it’s just not the same. The patterns of brain activity don’t show those four distinct stages.
Mammalian sleep happens in stages, starting with very light sleep - where we’re easily awakened by noises - and moving to deeper sleep that’s harder to rouse from. Then, we enter what’s known as REM, the dreaming phase, and after this, we’re back where we started, with light sleep, and the cycle restarts. In humans, each sleep cycle is about 90 minutes long.
Still at the zoo, Dr. Lukas and I hop in a golf cart and we’re off to see a notoriously sleepy animal: the koala.
LUKAS: This is one of our beautiful koalas, and we’re seeing her exhibited here in a set of branches that are designed to be a comfortable resting spot for koalas. They do spend a lot of their time sleeping.
20 hours, in fact. This one - a graceful grey creature with big fuzzy ears - sits in the crook of a low shade tree, her chin nestled among the branches and her paws lazily hugging the trunk. Koalas sleep so much in part because it helps them conserve energy, though, says Lukas, there’s no easy answer for why some animals need a lot of sleep and others don’t.
LUKAS: Well, that variability is what’s so beautiful about nature and biological diversity. I mean all of these animals - we’re seeing them in a zoo setting - but they all evolved in a natural environment where they are competing and essentially figuring out, over the years, how to survive and reproduce.
Sleep is one of those adaptations for survival.
LUKAS: From sharing your habitat with other animals... oh, hello.
The koala bear just woke up.
LUKAS: She just picked up her head and looked at us and is quite beautiful and quite awake right now - but yes, the timing and duration of sleep are linked to an animals’ health and ability to survive. It makes sense, evolutionarily speaking, for humans - who rely on vision to get by - to bed down at night and save energy for the sunlight hours. And, if we lay low at night we’re less likely to become lion snack.
For other animals, nighttime is the right time to be active.
FULLER: I don’t know how they manage to sleep upside down like that but I guess you see other animals like sloths, that can do that as well. So they will sometimes sleep in a position that seems improbable because he’s supporting all of his weight with his hands but he’s still asleep.
That’s grad student Grace Fuller again, and she’s spotted her animal of interest: the pigmy slow loris. The loris is a nocturnal animal, about the size of a squirrel, with fingernails instead of claws and large eyes that allow for night vision.
FULLER: So they’re sort of the little shift-workers of the animal world. And a lot of times you find this in animal ecosystems, in that one way to share a habitat is to be active at night instead of during the day.
(Whale sounds)
No, that's not a sound you'd hear at the Cleveland Zoo but the sleep behavior of marine mammals, like whales and dolphins, are among the most unusual and fascinating. They continue to swim while they're asleep. Only difference is when sleeping, they can swim in big circles near the surface of the water. They’re able to do this because only half of their brain is asleep. The other half? It’s awake. You could call them the ultimate multi-tasker, able to swim to the surface for air while also reaping the benefits of sleep.
And getting some shuteye doesn’t necessarily mean an animal actually has to shut its eyes - cows tend to sleep with their eyes open. And horses? They usually stand when sleeping.
Gorillas, on the other hand, appreciate creature comforts like big piles of hay to get cozy and build nests.
(Elephant trumpeting)
Elephants too will seek soft spots for sleep. When they feel comfortable and safe, they’ll take a load off - four or five tons, as the case may be - and actually lie down, on their side, for about four hours each night.
For all its quirks and mysteries, the need for sleep is a common thread between animals as wild as the big cats, as tame as tabbies, and as brainy and complex as humans.