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.
Millions of birds make arduous journeys of thousands of miles every year to migrate with the seasons to breed and seek food supplies.
In the Americas, birds fly north from South America and the Caribbean to the US, starting in the early months of the year, before returning.
An animation produced by Cornwell University shows 118 migratory species in the Americas, some beginning their journeys north in February, with the largest movement in March and April.