It looks like reports are centered around Fordham & Princeton ( https://goo.gl/maps/uBYw5WVwEyH2 ). Is there a trail here?
Hotspot birding ( http://www.hotspotbirding.smallfineprint.com/hotspotdetail?r=L275480&days=15 ) and this 2009 flyer for the Montgomery bird club ( http://www.montgomerybirdclub.org/newsletters/2009_Aug.pdf ) both reference this location. The Rockville city website for Upper Watts Branch park gives basically no information, and the intersection it gives at College & Nelson doesn't seem to have a trailhead (or parking) on google streetview. http://rockvillemd.gov/facilities/facility/details/Upper-Watts-Branch-Park-57
Thanks!
Doug
-Doug