I was kayaking in a back area of Oyster Bay, Long Island, NY September 21, 2022 and saw these birds sitting on the water atop schooling baitfish. There were smallish groups of them (~10 to 15 individuals) scattered here and there on bait balls in the bay - perhaps about 7 groups of birds that I could see (I think, I was not close enough to all to be sure they were all the same bird, to be honest). TOD I was with them was about 11am - 1pm, on the way from high to low tide. (The birds were there before I arrived and remained after I left.)
The birds mostly sat there, bobbling quietly, occasionally rising out of the water to grab a baitfish if the snappers (the fish, not the turtle) underneath the bait forced a bait boil at the surface. If the bait ball moved the birds flew a few yards to stay with it, but otherwise they simply sat on the water (they may have already gorged once for the day, or perhaps their feeding habit is to wait for surface boil chaos?).
I have a few photos in which you will see...
GSS: Birds were gull-like in shape but sleek, about the size of a smallish or medium gull. The wings were pointed and long for the body - in fact, when folded they not only were longer than the bird's tail but scissored across each other at the tips. Beak gull-like in shape with a bit of downslope and hook at the end.
Color: Birds mostly white. Tail (top and bottom) and front of head (top and ventral) are white. Breast white on most, though mottled gray on a few (immatures?). There is a partial light gray cap along the back of the head from about the level of the eyes down along the nape - it looks like it might wrap around to be a light gray ring at the top of the breast/bottom ventral neck, but I'm not sure if that's an artifact of shading in the photos as my little water camera is not the best. The wings were medium gray across the top, with wing underparts looking very light (white or light gray) but darkening to a sooty dark gray toward the tips. Legs, beak, and eyes are all black.
There are lots of migrants coming through now, so I'm not sure if I'm seeing a bird that's here year-round but normally not noticed if it's on shore, or whether I am seeing something that only comes through with the bait migrations.
I tried some online search wizards but do not come up with the correct looking bird. Thanks for any assistance!