A Harrier landed in the marsh north of the Powder Point Bridge, and when viewing it with binocs I noticed a largish dark bird on ground about 100 ft from it. Assuming it to be a crow, I stayed on the Harrier (handsome male) but then the dark bird moved closer and into good view, and I realized it wasn't a crow. My next thought was Coot but when it turned and revealed its full profile, no question it was a big rail!

These photos show the rail at coordinates: 42.059661,-70.652364. The photos were taken from inside my car at 42.059348,-70.648120 using my Canon Powershot SX70 HS at significant zoom. Getting closer was not an option due to flooding of the marsh. The image resolution is sub par but still helpful for documentation. Can't tell with certainty whether Clapper or King, but the saltmarsh setting and its very dark plumage says Clapper, and I had a Clapper in July, 2019 ( https://ebird.org/checklist/S58373508). It is uncommon on Duxbury Beach at any time, but especially so in January!