I took a short walk along the canal from the Brookmont area (near the DC line) this morning.  About 1/4 mile before the Little Falls pumping station I came across a Mourning Warbler in the vegetation overhanging the canal.  Looks were not great but it was calling frequently.
 
Small numbers of neotropical migrants were scattered amongst the chickadee/titmouse flocks including Blackburnian, Parula, Magnolia, Black and White and American Redstart.  Also a Warbling Vireo singing in a sycamore like it was a spring morning.
 
Clive Harris
Cabin John, MD