Dear Eden,
I live close to a natural area with lots of birds of prey like hawks and eagles. I love to watch them sit in ginormous nests on top of electrical poles. Or swooping around in big circles while they search for a meal.
I talked about why they circle with my friend Jennifer Phillips. She’s a wildlife ecologist at Washington State University. She studies the relationship between birds and the environment.
She told me that birds of prey fly in a circle because they’re riding warm air currents called thermal updrafts or thermals. As the sun heats the Earth, some pockets of air get hotter than others. That warmer air rises. Birds can hop on those warm, rising thermals and ride them. That saves energy.
“They’re able to catch the thermal and spiral up,” Phillips said. “If they’re searching for prey, they might circle an area for a while. They’re scanning for small mice or insects or whatever they might be hunting.”
Birds also ride thermals when they’re traveling long distances—like during migration. It’s like hopping on a moving sidewalk or escalator. The birds can rest and glide while thermals carry them along. Or they can fly faster with the extra boost from the thermal.
If that sounds fun, birds seem to agree with you. Phillips told me that sometimes it looks like birds are swooping around and playing in thermal updrafts.
Riding thermals helps birds of prey hunt because their eyes are on the front of their heads—like our eyes.
“They have binocular vision just like we do,” Phillips said. “If they’re staying in the same spot and circling in one area, they’re focusing on what’s below them.”
That excellent eyesight—along with curved beaks, sharp talons and an all-meat diet—is what makes them birds of prey.
But small birds that forage for food sometimes circle, too. They ride thermals to migrate or for fun. Sometimes they hop in a circle around a food item on the ground—like crumbs in a parking lot. Unlike us, their eyes are on the sides of their heads. So, they have to approach a food item from a circle to really see it. Plus, circling helps them scan for predators or other dangers nearby.
It turns out birds circle for lots of reasons. If you watch carefully and think like a bird, you may be able to figure out exactly what they’re doing.
That’s what I do when I watch birds of prey near my house. When it comes to understanding bird behavior, owl never give up.
Sincerely,
Dr. Universe