Hi all terners,

I just uploaded some photos to "birdingperu.com/picsfiles" myself in
response to Gunnar's photo of a flying tern. These photos are of South
American Tern (Sterna hirundinacea), Common Tern (S. hirundo), and
Arctic Tern (S. paradicea) which were all present together in the same
flock. I included the following comments with the photos:

" Here is a collage of tern photos that I took during the October
2005 Congreso in Chiclayo. All these terns were roosting on the beach
at Puerto Eten. Notice the larger size, longer, heavier bill, and
*black enclosing the eyes* of the Sterna hirundinacea (white meets the
underside of the eyes on both S. hirundo and S. paradisea). S. hirundo
also have a slimmer build, and more obvious dark along the leading
edge of the wings. S. paradicea have much shorter legs, a "puffier"
head and very thin bill. Both the latter two species also have "dark
headphones" which are lacking on S. hirundinacea.

I cannot comment on differences in flight because I have not had much
experience studying S. hirundinacea in flight. However, I can direct
your attention to some nice photos of S. hirundinacea in flight on
Arthur Grosset's website:
http://www.arthurgrosset.com/
(click "south american birds" and then "South American Tern")

The black-enclosed eye seems like a very powerful ID mark, at least
when perched (when it is easier to see), but has never been
illustrated in a field guide that I am aware. I have compared
specimens to be sure it is a real character, and it holds up well!"

It is Al Jaramillo's Birds of Chile that mentions the "headphone"
effect on S. hirundo (notice the little black nicks coming down the
sides of the head behind the eye which are missing on the other two
species). Based on this mark, as well as the apparent lack of black
surrounding the eye, I would conclude that Gunnar's bird is a Common
Tern. Finally, it appears that adult South American Terns retain a red
bill in basic plumage whereas Common Terns' bills become black. Based
on the wing pattern, I'd say Gunnar's bird is an adult in basic
plumage (which in Jan would suggest a Boreal breeder anyway), so it
should have a red bill if it is a South American Tern. I suspect Al
would have more to say on this, though.

Saludos,
Dan Lane
LSU Museum of Natural Science
Baton Rouge, Louisiana, USA

and

Field Guides Inc.