I looked at June's pictures, and agree with Bob Ringler that the bird in 
full alternate plumage on the right of Photo #5 is probably a 
Black-headed.  While it's not possible to see subtleties of color 
(Black-headed's hood is dark chocolate brown rather than black), I am 
struck by how red that bird's legs look in a photo where you can hardly 
make out the color of the other birds' legs.  Adult Black-headeds show 
brighter crimson-red legs than the more subdued orange-red of 
Bonaparte's.  And as Bob notes, the way the hood does not extend down the 
hind neck is more typical of Black-headed.

The photos of the gulls in flight do not provide much help, unfortunately, 
or it might be possible to see the longer wings of Black-headed and/or the 
distinctly dark areas on the underside of the primaries.

Mike Bowen
Bethesda, MD

At 08:46 PM 4/2/2005 -0500, 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

D. H. Michael Bowen (Mike)
8609 Ewing Drive
Bethesda MD 20817-3845
Tel/Fax: (301) 530-5764
e-mail: