To answer an offline question and hopefully clear up any confusion: 
The Yellow-throated etc. Warbler and the etc. nuthatches and siskins were in the Lyndon Baines Johnson Memorial Grove, which is on Columbia Island.  The grove is currently accessible only from southbound GW Parkway, between Memorial Bridge and the 14th Street bridges (I 395).  More information can be found at this link: http://www.nps.gov/lyba/.  Too many LBJs.  

Good birding, 

Rob Hilton
Silver Spring, Md.