bird burst
From Glossary of Meteorology
Radar echoes caused by flocks of roosting birds that take to the air as a group and fly away in different directions.
Bird bursts typically occur near sunrise and have ring-shaped reflectivity signatures with weak echoes in the center and maximum reflectivity in circles that expand with time around the roosting site. In Doppler radar observations, the velocity signature resembles that of a microburst at low levels.
