Below is a post I just made to Va-bird that maybe of interest to my Md.
birding friends.
NOTE:  Riverbend park is just across the river from about Swains Lock  on
the C&O canal.

*Subject: BROAD-WINGED BONANZA: A River of Raptors*
From: Donald Sweig <skybirds.d AT gmail.com>
Date: Sat, 18 Sep 2010 15:15:17 -0400

I went over to the meadow area of Riverbend Park (Fairfax County) this
morning  to see if I could find any migrants. I soon ran into some other
birders and spent 2 -3 hours birding with Ralph Wall (whom I have known for
years) and with Chris Farabaugh and Kal Kalburgi (both of whom I just met
this morning). It was a slow morning, but we saw a few nice birds: a
Philly   Vireo; a Tennessee warbler; Common Yellow-throats, Magnolias, a
Blackburnian, Redstarts, a Great Crested, Brown Thrasher, Parula, *etc*.
We walked into the trees on the far side of the meadow  to check that area
as well. About 9:40, as we turned around to return to the parking lot, Chris
spotted a bunch of birds flying across the horizon over the meadow.
Instantly, when I got them in view,  I yelled,"Broadwings. We can see them
from the meadow."  We ran down the trail and arrived just in time to see the
35-40 Broad-Winged hawks disappear over  the trees.  A minute or so later,
someone said  "there's more up here."  Directly overhead was a kettles of
maybe 100 Broadwings. "And more to the right" someone said.
Indeed, to our right, streaming in from the N.E. was a line of Broadwings;
then another kettle (maybe 200 birds), more streaming,  and another Kettle.
We soon  had a virtual River of Broad winged hawks streaming across the sky
above us (not too high either, we could clearly see the black band on the
back edge of the wings and the white tail bands) from the N.E.to the SW,
with several very large kettles (150-200 birds)  along the way. This was
clearly the  migration  flight -path for the Broad-wingeds this morning.,
We watched this amazing spectacle unfold for over 45  minutes. Eventually
the path of the stream drifted a bit to the South and began to get lost
behind the trees.  I have never seen anthing like this in all my years of
serious raptor watching; not even at any hawk-watch; not even close.  It was
truly astounding.  As we were about to leave the meadow, Chris found yet
another kettle just above the horizon to the South.  I told them  I would
post what we had seen and said I thought we had seen 1,500 or more
Broadwings. Both Ralph and Chris said they thought we saw at least 1,800 to
2,000 birds ( all in less than an hour!); and it could easily have been
more.  It may have been a once in a (my) lifetime experience. However,in the
hope that there will be more Broadies tomorrow  (a good probability) and
that they might be on the same flight-path (possible), I plan to be in that
meadow again in the morning.  I can't promise more hawks, but wold love to
have some more  eyes to scan the skies if anyone would like to come out and
try.



-- 
Donald Sweig
Falls Church, Va.