How long do animals sleep?

Hi, this is Aya from the support team at Datawrapper. This week, I want to share a little fact I learned about sleep patterns in different animals.

Earlier this year, I was staying in an old house that had been uninhabited for at least a few decades and was under renovation. One night, I woke up to use the bathroom and realized there were hundreds of bats flying around in the house. How did I not notice them at all during the day?

I knew that bats were nocturnal, but what I didn’t know was that they spend the majority of their time sleeping. For example, the average sleep time for little brown bats in captivity is 19 hours per day. This had me curious about the sleeping patterns of other animals. I found some data on sleep in different mammalian species in a paper from 1976 (which is old, but hopefully not too old in the context of evolutionary biology).

Larger mammals and herbivores sleep the least

From the chart, you can see that herbivores, who eat only plants, tend to sleep less than omnivores or carnivores. This makes sense as herbivores need to be more alert to protect themselves from predators.[1]

I was also surprised that bigger animals tend to sleep less, the least being the elephants — they only sleep around 3 hours! But that’s supported by observations from more recent studies on elephants:

Bigger animals generally tend to sleep less, probably because they have to spend so much time eating. “Elephants can eat up to 300 kilograms of food a day, so obviously it takes a long time for the trunk to get all that into their mouths, and that leaves less time for sleep.”

(Elephants sleep for just 2 hours a day – the least of any mammal), New Scientist 2017)

Other weird animal sleep patterns

Some other fun facts I learned while researching how different animals sleep:

  • Some marine mammals, fish, and birds experience something called unihemispheric sleep where one half of the brain is always awake while the other half sleeps. This allows them to keep swimming and flying while sleeping.[2]
  • Meanwhile, walruses barely sleep and can go up to 84 hours without sleep while swimming in water.[3]
  • Newborn dolphins and killer whales and their mothers do not sleep for a whole month after birth, while humans get the most sleep of their lives as newborns.[4]

And I could go on!

To answer my own question: Bats can afford to sleep for so long because they are very efficient feeders. A brown bat can eat up to 100 percent of its body weight every night — that’s approximately 1,200 insects per hour! And they have plenty of time left over to relax.

That’s it from me for this week! If you know any fun facts about sleep or have any feedback, get in touch at Thanks for reading!

  1. Clues to the functions of mammalian sleep (Nature, 2005) ↩︎
  2. How do Whales and Dolphins Sleep Without Drowning? (Scientific American, 1998) ↩︎
  3. Behavioral sleep in the walrus (Behavioural Brain Research, 2009) ↩︎
  4. Newborn dolphins go a month without sleep (New Scientist, 2005) ↩︎