Black swifts love moonlight — the brighter the better. A recent study found that the birds climbed to their highest altitudes when the Moon was full. But when the moonlight was blocked by an eclipse, they dropped in a hurry.

Researchers attached small trackers to a group of black swifts in Colorado. They then tracked the birds during their 4,000-mile migration to the Amazon Basin in Brazil. It took about eight months for the small birds to make the trip — with more than 99 percent of their time spent in the air.

During the day, and on nights with little moonlight, the birds stayed at altitudes of a few hundred to a few thousand feet. When the Moon was full though, they soared to two or three miles — possibly to grab high-flying insects.

On the night of January 20th, 2019, the birds were flying when the Moon was eclipsed. And they didn’t seem to like it. They quickly dropped thousands of feet. And when the eclipse ended, they climbed higher again.

This isn’t the first time animals have been seen to change behavior during an eclipse. Animals that like the light tend to slow down—including mosquitoes—while those that prefer the dark tend to get more active.

The black swifts usually head southward around September. So depending on where they are right now, they might experience that roller-coaster ride again soon. That’s because there’s a lunar eclipse coming up on Monday night. More about that tomorrow.

Script by Damond Benningfield

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