This bird was observed and photographed in dense fog on exposed tidal flats (between 9:40-10:00am - approx 1 hr after low tide) at the east end of the Powder Point Bridge. The bird was with of a flock of approximately 100-150 Terns most of which were Common Terns along with a handful of Forster's. Conceivably there may have been a Roseate or two as they are in the area in the summer. A number of Laughing and Ring-billed Gulls were intermingled as well. (please excuse the focus in these photos - they were taken with a handheld camera using a 100-400 zoom lens at full extension - in the fog. (Too much for the camera's autofocus and image stabilization capabilities to compensate for most of the time!)

While the bird was part of the flock, moving whenever they moved, it tended to prefer to be at the edges making photographing it feasible. When the flock would flush it would typically be among the first to return and alight on the flat.

It seemed the slightest bit smaller and more refined than the Commons which shows up in a couple of the photos. The bill seemed a bit narrower than that of the Common and a light or yellowish tip to the bill can be seen which, while not a Common Tern thing, may be seen on some winter plumage Forster's terns (pg. 107 Olsen & Larsson Terns of Europe & North America, Princeton University Press 1995 says a Forster's can have a pale "extreme tip" to its dark bill).

In that same reference text (pg 9), the author says "Colour variations such as leucism and albinism are extremely rare among the terns. I do not know of any instances of color aberrations in terns." I made a quick search on the internet and couldn't immediately find examples of leucism and Common Tern - though I did find a photo of a partially leucistic Caspian Tern taken in late March, 2012 in Baja, California.

Quite apart from the exceedingly unusual scientific considerations, this was a gorgeous bird. I could not take my eyes off it. The whole experience, enhanced by the dense fog, had a surreal quality that in many ways reminded me of my first sighting of the Ivory Gull in Gloucester, MA in 2009. Unfortunately I was unable to get any good flight photos (though I've included a few poor quality shot just to give the feel of the bird in a flight context), but even without the aid of photos, I'm confident I won't forget how bright it looked among the "regular" terns as they swirled up and over the flats in the dense gray fog. A very, very cool bird!

I suspect the flock will have moved on when high tide covered the flats, but I will check tomorrow in hopes that it stays and I can see and photograph it in better light. If successful, I will update this gallery. and post to MassBird