Elegant tern is well known to have a lot of variability in the bill, though this one definitely emphasizes the long, relatively narrow bill with fairly typical coloration. An article from the San Diego Atlas project notes that an Elegant Tern's bill is about 5 1/2 times as long as it is thick whereas Royal (and Caspian) have bills about 3 - 3 1/2 times as long as they are thick.
The bill heft was probably the most helpful mark for me. The bird on the right, and the front-most of the birds on the left, are clearly Elegants. The juvenile is a Royal Tern. The rear-most bird on the left (I'm pretty sure) is a Royal Tern based on the bill. Once it reaches full winter plumage it will have even less black on the head, currently its crown is fairly comparable to the Elegants:
The pinkish hue to the underparts was also more pronounced than I've seen before in terns (I've never seen a roseate), and is apparently fairly unique amongst the larger terns.
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Here's a juvenile. These have a yellower bill than the adults. I think I over-cropped this image for the blog. On the original there's a nicer symmetric X formed by the reflection of the spread wings:
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The bird on the right is the one that stimulated me to write this blog as I did a fair amount of reading on the web. I'm sure glad I saw it in San Diego and not at Tiscornia.
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My best guess is that this is a one-year-old bird that's for some reason way behind on its moult. I don't have the Olsen and Larsson big tern book or the waterbird Pyle however.
Finally, one last comparison of Royal Tern on the left and Elegant Tern on the right, showing comparison of size, bill shape, and the typical amount of black on the crown.
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Since I couldn't get blogger to link directly to papers found in the Sora database, here's the other citations I used:
Finally, one last comparison of Royal Tern on the left and Elegant Tern on the right, showing comparison of size, bill shape, and the typical amount of black on the crown.
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Since I couldn't get blogger to link directly to papers found in the Sora database, here's the other citations I used:
author unclear. Notes on the Elegant Tern as a Bird of California. Condor: 1920's?
Monroe Jr, BL. Observations of Elegant Terns at San Diego, California. Wilson Bulletin: Vol 68, No. 3, 1956.
Paul, RT, and AF Paul, B Pranty, AB Hodgson, and DJ Powell. Probably hybridization between Elegant Tern and Sandwich Tern in west-central Florida: The first North American nesting record of ELegant Tern away from the Pacific Coast. North American Birds: Vol 57, Num 2, 2003.