A huge swarm of birds migrating is nothing unusual - flocks can fly thousands of miles undetected.
But in a rare event on Monday, US National Weather Service radar captured birds migrating from South America over Florida.
Atmospheric conditions caused the systems to detect the birds, which took hours to fly over the Key West station.
The group measured at least 90 miles (145km) in radius, according to meteorologists.
In 2017 a swarm of migrating Printed Lady butterflies was detected by radar over Colorado, but the phenomenon is rare.
A GIF produced by the Weather Service shows the migrating birds in green and yellow, and rain depicted in blue.