I stopped by Hains Pt., DC yesterday (8/20) morning on my way to work. 
It was pretty quiet except for a MERLIN perched high in a tree at the
south end of the golf course (along the maintenance road).  I went back
today (8/21) and saw a different MERLIN in the same general area (I
believe both were adults but plumage and size differed - presumably 1
male and 1 female).  Today I also saw an AMERICAN KESTREL in the same
area along with a few migrants.  The warbler highlight was having 5
YELLOW WARBLERS together in one tree - a family unit?  Also present were
1 AMERICAN REDSTART, 1 MAGNOLIA WARBLER, 1 SCARLET TANAGER, 2 BOBOLINKS
(heard flying overhead), and a young EASTERN TOWHEE (did they nest
here?).

This is not the first time I've seen MERLIN at the Hains Pt. Golf Course
in August.  I have a note of seeing one on Aug. 31st, just not sure
which year (within the last 2 or 3).  And Jim Moore's report from
Rockville suggests a movement afoot.

Good birding,
Paul Pisano
Arlington, VA