     Mount Washington Observatory  National Oceanic and Atmospheric Administration  Subaru of America  National Science Foundation |
Apparently Starlings were leaving their roost in successive waves. Each major bird departure episode caused a new ring echo to appear. This all took place on a quiet early morning; there was nothing like meteorological microburst activity going on.
Pat Kennedy
This image contains several concentric radar echo rings. When a series of these images are animated, the successive rings can be seen to expand outwards like ripples after a stone is dropped into a pond.
CSU-CHILL Radar