Like Barn Swallows, terns move fast, change direction suddenly, and are almost never seen perched and resting. This quality also makes them difficult to identify. Here David Hauer has succeeded in imaging a tern in flight, no small feat. But what kind of tern is it? The black half cap back of the eyes and the black bar at the front of the wings point to the Forster’s. Forster’s Terns can often be seen on the North Basin, and I managed to photograph one in September 2016. But the yellow bill of this bird doesn’t match any Forster’s Tern pictures in the three big sources, Cornell, Audubon, and Wikipedia. The bill in a Forster’s should be black, except for a breeding adult, where it should be red or reddish with a black tip. So, rule out Forster’s. There is a group of terns who have orange or yellow bills. This includes Elegant Terns, Royal Terns, Greater and Lesser Crested Terns, and Cayenne Terns. The Wikipedia writer says that hybridization is not uncommon, and where birds are out of their normal range (“vagrants” — I hate that word), identification is much more difficult. The Merlin bird id app, which is sometimes wrong, thinks the photo above is of an Elegant Tern. And indeed, in the Cornell bird lab website, there is a photo of an Elegant Tern, a non-breeding adult, which could be a match for David’s tern. Conclusion: this is probably an Elegant Tern, and a new entry on the chavezpark.org bird list. Congratulations, David Hauer!
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