June,
   They look like Bonaparte's Gulls.  When I see them on the lakes in migration they are almost always with Ring-bills.  At this time of year they can have a wide variety of head plumages.

Bob Ringler
Eldersburg MD

 
---- June Tveekrem <> wrote: 
> Today around 4:00 pm I saw a flock of gulls at Centennial Lake.  About 
> half of them were Ring-billed, and the others were small gulls with 
> black or black-and-white heads.  I thought maybe Bonaparte's, but Sibley 
> says "Bonaparte's rarely mixes with larger species, but Black-headed 
> often consorts with Laughing and Ring-billed Gulls."
> 
> I have posted 10 photos at this URL:
> http://tinyurl.com/5fup4
> 
> Unfortunately, the photos are poor.  Partly this was due to shooting in 
> the rain, and partly because just as I was getting closer to the gulls 
> for some better pictures, a group of people came along and scared away 
> the birds.  I got a few photos of the gulls in flight while they 
> circled, then they were gone.
> 
> I'm quite curious to know what I saw, so I hope ID is possible from the 
> pictures.  By the way, these photos were cropped only; no effort was 
> made to improve them by photo editing.
> 
> -- 
> June Tveekrem
> Columbia, Howard Co, MD
> tweekiebird AT toadmail DOT com