Made a visit along Merrimack St. just before 6PM looking for the crows in staging mode. Lots of crows observed swirling around over the Merrimack River and landing on the new Mill 240 building on the north side of the Merrimack River. Observations made under overcast skies, wind from NE at 7MPH, and temp at 64F.
This photo show a section of the rooftop on the south side of the building. Mill 240 is located on the south side of 250 Canal St.; the building under renovation at the edge of the Merrimack River, is a former 7 story paper mill building; it is now under construction and being made into almost 200 apartments, Phase II of Washington Mills. This has been a popular staging area over the last number of nights.
Before heading to overnight roost, crows will congregate, or stage, in some area away from the final roosting site, usually an hour or two before complete darkness. Here the crows spend a lot of time calling, chasing, and fighting. It is amazing to watch the antics during he chasing and fighting that goes on. Right about dark, the main body of the group will move toward the final roosting spot. Sometimes this final movement is relatively quiet, but usually it is still quite noisy.
Crows typically come together from several separate pre-staging areas, heading to one final staging area where they all coalesce, then everyone heads to the final roost. The final roost can be a cohesive group in a single woodlot, or it can be rather diffusely spread out over quite a wide area of suitable trees.
Reference cited: Kevin McGowan, Cornell Lab of Ornithology, Frequently Asked Questions About Crows; http://www.birds.cornell.edu/crows/crowfaq.htm#roost