I don’t have an explanation for it. The activity over water near the shoreline most likely indicates shorebird migration and would not explain high density of songbirds birds over our parks. If you look at the landing density on both mornings of your maps, it concentrates fairly symmetrically at sites of radar stations in NY and NJ. This is expected as when birds, start to land, their altitudes drop so that the birds in areas further from the radar no longer reflect as they are “under the radar”. If the concentration is very asymmetric it could suggest birds concentrating in one or more geographic areas, but here (except for the shoreline migration) it looks pretty even.
The best I could say is that the migration was pretty diffuse and covered a wide swath. But if you look at paul hurtado’s map for night before last it looks even denser.
So it would be hard for me to explain Chris Cooper’s tweet of a dozen Cape Mays in one tree at Central just based on that landing pattern. Perhaps the shorebird migration is a clue that densities of birds were greater than they appeared to be based on reflectivities. But I’m not an expert, just a dedicated amateur. Any other comments are welcomed.