The bird stayed in this position for most of the 40 minutes I was with it. When a black-capped gull sized bird was described to me on the phone, I had locked into my head Greater Shearwater - especially since a Manx was seen off Duxbury Beach the previous weekend. Needless to say I was very surpirsed to see that it was a Jaeger.

Having not done much pelagic birding and only seen Jaegers from a good distance, I needed to grab the field guides to sort this out. This photo shows a the big thick two-toned bill that belongs to a Pomarine. Also the black cap stretches down below the gape of the the bill which is distinctive.