Just before daybreak Wednesday, something unusual — but not totally out of the ordinary — showed up on the local radar.
The video above shows what appeared to be an expanding circle of echoes across the Chesapeake Bay near Chestertown, Maryland, that disappear quickly several minutes later.
The radar detected a flock of birds, according to the National Weather Service.
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During the early morning before sunrise on days with high pressure and calm wind, the radar beam tends to bend downward toward the ground within several miles from the radar site itself.
The radar also is sensitive to detecting large masses of biological targets when there is no precipitation remotely close to a region.
That happened last summer when lots of cicadas were in the region and spotted on the radar.
Wednesday’s radar echoes at 6:28 a.m. showed a flock of birds, initially together, but separated and went their own way and outside the Sterling’s radar coverage area.