I love how humans use figures of speech about animals to describe their behavior. An early bird is someone who likes to get up early. A night owl is someone who loves to be awake late at night—like an owl.
I talked about why owls stay up all night with my friend Dr. Marcie Logsdon. She’s a wildlife veterinarian at Washington State University.
She told me that for many owls, the dark is a good time to catch a meal.
“Owls are just taking advantage of a time when they can excel at finding prey because there are a lot of other things that are active at night, too—like rodents,” Logsdon said.
It’s such a good time to hunt that those owls’ bodies have adapted to the dark. That’s why they have big round eyes. Big eyes with large pupils let in more light. That helps owls see in darker conditions.
Those big eyes can’t move around like our eyeballs—because they’re not balls. Owl eyes are shaped like bells. Their skull bones hold those bell-shaped eyes into their heads with no space to move. To look around, an owl turns its whole head.
The internal structure of an owl eye is special, too. Most vertebrates have rod cells and cone cells in their eyes. Cones detect colors. Rods detect light and motion.
Diurnal animals are awake during the day. There’s lots of light, so it’s useful to see lots of colors. It makes sense that diurnal animals have more cones than rods in their eyes.
Nocturnal animals are awake during the night. Since you can’t really see color in the dark, nocturnal animals have more rods than cones. Their eyes are optimized to detect movement—like prey sneaking around—even in very low light.
Owls use their ears to hunt at night, too. Logsdon told me scientists tested how well barn owls hunt for mice in completely dark rooms. They had no problem picking out those tasty squeakers in the dark.
“Instead of having nice symmetrical ears like we do, a lot of owls have slightly offset ears,” she said. “Sound hits them at slightly different times so they can pinpoint where the sound comes from. Some owls do that with the soft tissues—like our ear flaps. Some owls have changes in their skulls that help offset their ears.”
You might be surprised to hear that not all owls stay up all night. Some owls are awake during the day—although that’s not as common. Some owls are crepuscular. That means they prefer to be awake at dawn when the sun is coming up or dusk when the sun is going down. Some owls are cathemeral. That means they’re awake at random times without any real pattern.
That’s like me. Cats have random periods of sleep and wakefulness. That’s how we get the best figure of speech of all: the cat nap.