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Strange Colorado radar image likely caused by thousands of migrating butterflies

BOULDER, Colo. -- The National Weather Service in Boulder posted radar images to social media on Tuesday showing what it said was likely a flock of birds moving across several Colorado counties, but on Wednesday, it amended that to say it was most likely migrating butterflies.

The image was captured on the radar at Front Range Airport and officials said it's a common site this time of the year.

Jeff Wells said on Twitter it could have been migrating cranes, waterfowl, swallows or blackbirds.

New high-tech radar can pick up such instances of a mass of migrating birds, providing the unique images such as from Tuesday.

But on Wednesday, the National Weather Service said it's believed migrating butterflies were the cause of the radar signature and not birds.

"Things with big wings need to fly together in the same direction with the wind to generate that signature in ZDR (purple image)," the National Weather Service said.

"Migrating butterflies in high quantities explains it."