KPAH Bird MigrationRadar returns from birds, insects, and aircraft are rather common. Echoes from migrating birds regularly appear during nighttime hours between late February and lake May, and again from August through early November. Returns from insects are sometimes apparent during July and August. The apparent intensity and areal coverage of these features are partly dependent on radio propagation conditions, but they usually appear within 30 miles of the radar and produce reflectitivy's of <30 dBZ.
However, during the peaks of the bird migration seasons, in April and early September, extensive areas of the south-central U.S. may be covered by such echoes. You may visit Wunderground for additional information on weather radar.
On July 22, 2008, a line of thunderstorms was approaching the radar site at the National Weather Service Office in Paducah, Kentucky. At the same time there was a migration of birds over northwest Tennessee. The birds were flying out of Reelfoot Lake. This lake was formed by the New Madrid earthquake, which occurred in the 1800s. These birds can regularly be seen on the weather radar site. This radar animation (from WeatherTap) is from 6:30 AM through 7:30 AM.
Here is another example that actually shows four different areas of migrating birds. This image was from August 6, 2008.