Russ Ruffing and I took a short walk along the Patuxent Branch Trail 
during lunch today and came up with a few notables:

Ruby-throated Hummingbird     1
Northern Rough-winged Swallow     6
Northern Parula     3
Chestnut-sided Warbler     1
Black-throated Blue Warbler     3
Yellow-rumped Warbler    3
Bay-breasted Warbler     1
Common Yellowthroat     2
Pine Siskin     1
and an Eastern Phoebe devouring a teneral Ashy Clubtail.  The horror!

Yesterday (5/11) I also had Stan Arnold's Canada Warbler, in addition to:
Northern Parula     1
Black-throated Blue Warbler     2
Worm-eating Warbler     1
Ovenbird     1
Louisiana Waterthrush     1
Common Yellowthroat     3

I recently added dozens of checklists for this trail to eBird.  You can 
see the list here if you're interested (it's still missing a few review 
species):
http://tinyurl.com/rbk4ld
Please add your own sightings to help flesh it out.

And, of course, there's Jo Solem's great website & trail checklist here:
http://www.howardbirds.org/birdinghowardcounty/PatuxentBrTrail/ptx_br_trail_overview.htm

Cheers,
Steve Collins
Towson, MD