I was out in this vicinity looking around for swallows around a little bit on Sat 
and Sun.  I looked along the river and south of Rt 4 to Jug Bay.  I found no 
swallows, but yesterday at about 12:30 I did see a large white raptor south of 
Rt 4, perched in a tree on the PG side of river.  It caught my eye because it 
was very white.  However, when I put my scope on it it was a only a light 
adult red-tailed hawk.  It was not as white as a Krider's race, and was simply 
a very pale adult eastern sitting in direct sunlight.

My experience looking at large perched falcons is limited to peregrines, but I 
have looked at many.  From any angle other than facing directly at you, they 
are not really white, as Cat described.  There has been one seen here twice 
that I know of in the last several weeks (unfortunately not by me!).

The most obvious large "white" falcon is the gyrfalcon, which I've never seen 
anywhere, and would be exceptionally rare in southern MD.  I've never heard 
of anyone seeing one anywhere in MD.

Another unlikely but possible large white raptor would be an adult northern 
goshawk.  This is a possibililty but also very rare down here, and they are not 
really "white" but can appear very light if facing directly at you.

Cat:  I don't know your experience level, but are you sure it was not an owl?  
There are two very white owl possibilities, and the most obvious is the snowy 
owl.  These are very easily identified, but perhaps could be misid'd as a hawk 
if seen from a vehicle passing by at 60 mph!  And the other possibility is a 
barn owl but they are also easily identified.  There have been no snowy's 
reported this season around here that I know of, but there are a few barn 
owls along the river in the vicinity of the report.

My guess is you either saw an adult red-tailed hawk or a barn owl.

Cheers-
Jeff Shenot
Crrom Md