How do hummingbirds sleep?Anusha Shankar:

Ooh this is an exciting question—I’ve spent the past five years thinking about just this!

Look at these infrared images from a crowdfunded project we did in the summer of 2017: The bird on the left is generating heat, keeping itself warm, while the one on the right is in torpor. It has allowed its body temperature to become the same as the air temperature and has stopped "thermoregulating," or maintaining a high body temperature.

Hummingbirds find a nice and sheltered place at night, and they latch onto a branch with their tiny feet, and then they go to sleep. Some of them ... use a strategy called torpor, where they can lower the amount of energy they use by about 85 percent. They do this by basically shutting down a bunch of their bodily functions—they allow their body to get cold as the night gets colder. You and I spend a lot of energy keeping our bodies warm so everything functions normally. Hummingbirds in torpor give up this "normal" function, and become more like lizards, in that they can get ‘cold-blooded’ in torpor.

Torpor is a tricky state to be in, because they can’t respond to outside stimuli for 20 to 30 minutes, until they warm their bodies back up. They take that risk just to have enough energy in their tiny bodies to make it to the next morning.

I recently wrote a blog post for National Geographic to talk a bit more about hummingbird sleep (includes videos!).

This post originally appeared on Quora. Click here to view.