18 Black Vultures were on logs and such by the river at Great Falls, straight out from the viewing platform.

No Bald Eagles were to be found when I was there from 9:30 am to 12:44pm.  Rain began at 10am, falling steadily for a while, then intermittantly.  However, there were also:

Canada Goose (2)
Mallard (8)
American Black Duck (3)
Ring-necked Duck (44)
Bufflehead (6)
Common Merganser (10)
Ring-Billed Gull
Boneparte's Gull (12)
Great Blue Heron (14; 11 were in a single flock moving downstream together)
Turkey Vulture (3)
American Crow
Blue Jay (3)
Red-bellied Woodpecker (4)
Downy Woodpecker
Hairy Woodpecker
Pileated Woodpecker (2, maybe 3)
Cedar Waxwing (82; 3 large flocks feeding on cedar by the canal)
American Robin (9)
Eastern Bluebird (9)
Carolina Chickadee (3)
white-breasted Nuthatch (2) 
Brown Creeper (4)
No. Cardinal (2)
Dark-eyed Junco (10)

Did find the Bald Eagles down at Sycamore Island (2 adults, perched near the nest), and also of note, between 1:10pm and 3:20pm:

Pied-billed Grebe
Common Merganser (7)

Good birding,

--
Frank Powers
Glen Echo, MD
Montgomery County