Steve Zubrick, the science and operations officer at the National Weather Service forecast office in Sterling, sent me a series of radar images shot early Wednesday morning.

They show an odd ring of radar returns (image above) that appears to emerge from the upper Chesapeake, near Pooles Island, and expand across the area.  He thinks it's a flock of birds, rising after dawn and fanning, perhaps to forage for the day. Here's Steve's note:

"For the past several mornings, beginning around 6AM EDT (1000 UTC), our KLWX 88D Doppler radar has shown an expanding ring of higher reflectivity values originating from an apparent point source of the Chesapeake Bay just north of Poole's Island near the mouth of the Bush River.

"I've attached a few images that show this phenomena. It's nothing unusual and happens quite frequently, not only here but in other parts of the country.

"When I've seen these before in this area, they've been mostly originating over land. This appears to originate over water (or marsh?) near the mouth of  the Bush River...or the land areas along eastern Aberdeen Proving Ground.

"Also, the 1021Z images show the reflectivity spike seen by the radar as the sun rises. Interesting."

He may be right. It could be birds. But what kind of birds are massed like that at this time of year? Any watermen or boaters out there who have witnessed anything like this around Poole's Island? What do you think?

UPDATE:  Just received email from Jerome A. Jackson, professor of ecological science at Florida Gulf Coast University. He took a look at the radar images and had this to offer:

"Yes, they are likely birds ... and a good guess would be that they are purple martins. Patterns like this are often produced as purple martins disperse from their communal roosts at this time of year. We are talking about roosts of thousands of martins. It would be very interesting to confirm that they are martins by going to the area shown and watching for them either in the morning as they go out to feed for the day, or in the evening as they return to roost.

"They gather in enormous flocks prior to migrating to the Amazon basin for the winter ... and usually roost near large bodies of water where they then move out to feed on the hordes of insects that are produced in the area."

Thanks to Baltimore Sun photo editor Jerry Jackson, for facilitating the exchange with Dr. Jackson, his dad.