Forster's Tern at Panamá Viejo

The effort of sharing one scope to scan the huge flock of gulls and terns at the Panamá Viejo beach on high tide was rewarded with the discovery of a Forster's Tern in winter plumage. The Junior Audubon group (Rosabel Miro, Darién Montañez and Junior Auduboner Rogney Quibilán) got great looks at the much smaller bird, that was standing in front of the other gulls and sometimes opening its wings to make sure we saw its wing pattern. It had an all-black bill, and its head was white from the forehead to the crown, turning slightly grayer around the nape. The black ear-patches were quite striking, reaching the eyes but not extending into the lores of the bird. The back was pearly gray, with just a hint of a dark carpal bar (much paler than the ones on the few Common Terns standing nearby). We were treated to brief looks at its open wings, and the pattern of the upperwing was also paler than that of the average Common Tern, especially first few primaries.
The flock was a big one, somewhere around three thousand birds, composed mainly of Laughing Gulls, but there were two Ring-billed Gulls (one adult in breeding plumage and a juvenile), and at least four Elegant Terns (only one in breeding plumage).