Mystery Bird: Least Tern, Sterna antillarum

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[Mystery bird] Least Tern, Sterna antillarum, photographed at Bolivar Flats, Texas. [I will identify this bird for you tomorrow]
Image: Joseph Kennedy, 16 August 2008 [larger view].
Nikon D200, Kowa 883 telescope TSN-PZ camera eyepiece 1/750s f/8.0 at 1000.0mm iso400.


Rick Wright, Managing Director of WINGS Birding Tours Worldwide, writes:
Another teeny tern. If that wasn’t your first thought, you might want to run back through the other tern images in this series and try to get a sense of what a big tern looks like, a medium tern, a small tern; you’ll soon find that very subtle proportions and relations within the bird itself, even absent any external basis for comparison, can help you sort them into rough size categories.
At the first level, this is an easy identification. Measured against the grains of sand, this is a very small bird, and the only very small tern in North America is the well- and aptly named Least Tern. The bill and legs of this individual are still yellow — unique among North American terns — and the white forehead is crisply set off from the rapidly molting black cap. The standard identification character for this bird in flight, the contrasty wing pattern, is also visible with the wings folded: note how the outermost primaries (the lowest long feathers in the folded wing) are jet black, while the others are gray. Spread this wing mentally, and you get the abrupt black leading edge of Least Tern’s wing (and you probably won’t be able to help hearing in your mind’s ear the distinctive little squeaky chatter of this bantam sternine).
A fly in the tern ointment? Of course. A straightforward picture-match in the North American field guides turns into a bit of a nightmare when we bring Little, Saunders’s, Yellow-billed, and Peruvian Terns into the mix. This isn’t a gratuitous wrench in the tern works, either — a couple of members of the group have strayed incredible distances (Large-billed from South America to Wisconsin, Whiskered from central Europe to New Jersey), and it’s probably not safe to put anything beyond these long-winged ocean wanderers. The challenge is acute in Hawaii, where both Little and Least Terns occur at nearly the same frequency, and any unseasonal or even mildly out-of-range small tern in North America should be made the object of scrutiny. Most of them will turn out to be Leasts, but we can always hope.
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About GrrlScientist

grrlscientist is the pseudonym of an evolutionary biologist and ornithologist who writes about evolution, ethology, and ecology, especially in birds. After earning a degree in microbiology (thesis focus: virology) and working at the Fred Hutchinson Cancer Research Center in Seattle, she earned her PhD in zoology from the University of Washington in Seattle, where she studied the molecular correlates of testosterone and behaviour in white-crowned sparrows. She then worked a Chapman Postdoctoral Fellow at the American Museum of Natural History in New York City, where she studied the speciation and distribution of lories and other parrots throughout the South Pacific Islands. A discarded scientist, she returned to her roots: writing. Formerly hosted by The Guardian (UK), she now writes about science for Forbes and for the non-profit think tank, the Evolution Institute and she writes podcasts for BirdNote Radio. An avid lifelong birder and aviculturist, she lives with a flock of songbirds and parrots somewhere in Germany.
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0 Responses to Mystery Bird: Least Tern, Sterna antillarum

  1. Sven DiMilo says:

    Roseate Tern?

  2. Ian "Birdbooker" Paulsen says:

    If you want to learn more about tern identification, consult this book: Terns of Europe and North America by Klaus Malling Olsen and Hans Larsson (1995).

  3. JPS says:

    Since the area around the eye is black and the forehead is white I’m going with least tern.

  4. Debbie says:

    I am going to say Interior least tern

  5. Jer says:

    A view from across the ‘pond’. I’d go with Least, personally. Legs and bill seem to be coming through largely yellow and the shape of the cap fits nicely. I’d be interested to see how they can be separated from our Little Tern, though. Must do more background reading!!

  6. JohnB says:

    probably a Least Tern

  7. Rick Wright says:

    Dear Jer,
    Sorry not to have been more informative about the identification of Little Tern. I was impressed again in April by just how like Least Little Tern is, and haven’t had a chance to do any re-reading–I do know that Little is supposed to have a whiter rump than Least. It was a lot easier when we called them all one species!
    Dear Debbie,
    How did you get to Interior Least Tern from this photo? Fill me in! I can barely distinguish the species from similar Sternula.
    r

  8. William F. Pennock says:

    I understand that the Least Tern-Sterna antillarum is an endangered species in some states,so it gives great pleasure to informe you that I
    had a sitting of this bird in Dorado, Puerto Rico, which is a Commonwealth of the USA in the Caribbean Sea(Mid-Atlantic Ocean). It’s flight when hovering at 10 to 15 feet before it dived to catch it’s prey was a dead ringer for it’s identification.Sorry I couldn’t get my camera to focus and shoot,since it was moving all the time. This bird has been spotted in PR before,but it is uncommon in this area.