Living the Scientific Life (Scientist, Interrupted)

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[Mystery bird] Marbled Godwit, Limosa fedoa, photographed at Galveston Island East Beach, Texas. [I will identify this bird for you in 48 hours]

Image: Joseph Kennedy, 1 June 2010 [larger view].

Nikon D200, Kowa 883 telescope with TSN-PZ camera eyepiece 1/1000s f/8.0 at 1000.0mm iso400.

Please name at least one field mark that supports your identification.


This species is comprised of a seemingly homogeneous population of birds. However, scientists have recently found that this species shows some geographic variation between breeding populations, can you tell me what that variation is?

ANSWER: Measurements of the two Alaska-breeding populations shows these birds have shorter wings and legs than the Great Plains-breeding birds. This paper went on to say this of the most diminutive subspecies of Limosa fedoa:

This limited Alaskan-breeding population … named Limosa fedoa beringiae … does not appear in the guide-books (Shorebirds, Sibley etc.) or on the maps, and may only differ in size (e.g.; shorter bill, wing and legs), but a lone male beringiae amongst a bunch of female fedoa could look tiny.

L. f. beringiae probably normally winters along the coast of Oregon and northern California amongst the more numerous [nominate] fedoa. No plumage differences are yet described, but the climate anomaly and geographical distribution (which may include a long over-ocean flight) may throw up some plumage and moult differences, perhaps worthy of extra study.

Daniel D. Gibson & Brina Kessel. (1989). Geographic Variation in the Marbled Godwit and Description of an Alaska Subspecies. The Condor 91:436-443 [free PDF].

Review all mystery birds to date.

Comments

  1. #1 Beardos
    June 21, 2010

    Upturned bill, barred tail … if this one also occurs on the eastern side of the Atlantic then it’s something I’ve been seeing annually for more than 30 years.

  2. #2 bardiac
    June 21, 2010

    The beak takes me to the Godwits, but from there, I’m lost. My Sibley’s shows four species: Bar-tailed, Black-tailed, Hudsonian, and Marbled.

    The breeding plumage of the male in each case is really distinctive either for reddishness or lots of striping. So, I’m thinking not a breeding plumage male.

    That leaves juveniles and breeding plumage females.

    The breeding plumage female Bar Tailed seems possible at first, but the picture shows a strong white stripe above the eye, and I don’t see that here. Similarly, the juvenile has a strong eye stripe. Also the geography seems off. (Sibley’s shows northern coasts and rare.)

    The blacktailed female also has a strong eye stripe, and more stripiness on the flanks than this bird. The juvenile looks quite buff-colored on the breast (not this bird, though) and has a distinct eye stripe. Also, the beak looks more recurved here than in the picture above.

    The Hudsonian female also has a strong eye stripe and lots of stripiness on the flanks.

    That leaves the juvenile Marbled. (The female marbled has stripey flanks, like the male).

    The beak color of the juvenile Marbled seems sort of pinkish in my book compared to a more orangey color in the adults.

    Would a juvenile be more likely to hang out in Texas rather than being up north?

    The female breeding plumage of the Blac

  3. #3 psweet
    June 21, 2010

    Bardiac, I’d be very surprised if this was indeed a juvenile (in other words, still in it’s first post-natal plumage). The date is wrong, since adults are still moving north through Illinois in late May. Also, this bird shows a lot of feather wear, with some obvious replacement in the secondary coverts — this wouldn’t be expected in a juvenile at this point in the year. (Actually, juveniles tpically migrate south quite late — September or so — and have usually molted out of their true juvenal plumage by then.)
    A quick perusal of O’Brien, Crossley, and Karlson shows that birds going into their first summer have a “limited and variable” molt, and can typically be identified by their worn, retained juvenal primaries. Both of these seem to fit this bird, since the timing is all wrong for it to be actively molting. And one-year old birds will sometimes hang out on the winter grounds, rather than migrating north without much chance of breeding themselves.

  4. #4 bardiac
    June 21, 2010

    Psweet, Thanks. I guess there’s a distinction between juvenile (before the end of the first year) and birds at the end of their first year? I wasn’t getting that, but was thinking that it was a first year bird that maybe hadn’t migrated?

    Thanks!

  5. #5 Adrian
    June 21, 2010

    The heaviness of the bill should remove all but one of the (potentially) four Godwits in the region and both Dowitchers.

  6. #6 PattyP
    June 21, 2010

    WhatBird.com says of the Marbled Godwit: “This species was long regarded as showing no noticeable geographic variation until measurements of birds breeding in Alaska showed these populations to have shorter wings and legs than Great Plains godwits.”

  7. #7 Ken Trease
    June 21, 2010

    Marbled Godwits have three distinct breeding populations. Two small groups, one in Alaska and one near James Bay, and the third large group in the north-central US and southern Canada. The nore northern breeding populations on average have shorter wings, legs and bills. The authors of the research paper I read speculate that perhaps the longer legs and bills of the grassland breeding birds might offer some advantage over the shorter bills of the tundra breeding birds?

  8. #8 psweet
    June 21, 2010

    Hi, Bardiac, sounds like you were right on in your thinking. To tell the truth, not too many birders actually make the juvenile/immature distinction. However, when dealing with shorebirds, so much of the ID involves aging the bird that being explicit with plumage helps, I think. So: The first set of feathers a bird develops are simply downy, with no feather vane. The next set, in many birds grown while still in the nest, constitute the juvenile plumage. Most species molt out of the juvenile plumage fairly quickly, but some will maintain it for some time. This applies to body plumage, of course. Tail and flight feathers are apparently too expensive to replace immediately, and most birds will maintain them until the following fall. Some of the larger hawks will maintain some of their primaries and secondaries for two or more years.
    After that post-juvenile molt, things can be more complicated, and there are various terminologies in use. Frequently, though, the next molt is only partial, and you can see contrasts between old and new feathers that help in aging birds. (For some, these molt limits are subtle, often on the wing coverts, and mostly useful in the hand.)

    In the case of shorebirds in fall, juveniles tend to be brighter and fresher looking than adults, with clean, crisp edging and other markings on the back and coverts. Except for a few species that molt before migrating so that we never see juveniles down here. (Purple Sandpipers, for instance)

    Incidentally, you missed a very useful ID feature on this bird that happens to be visible (it often isn’t on a standing bird). The tail is barred tawny and black. A Bar-tailed would be barred black and white, while the other two have black tails without any barring.

  9. #9 bardiac
    June 21, 2010

    Thanks, Psweet! It’s really helpful to me to get a sense of what to pay attention to better. I appreciate your explanation a LOT :)

    So a juvenile would be from hatching through the first feathers, then an immature would be after the first (partial or full) molt? And some birds retain immature plumage for a couple years (gulls, I think).

    Thanks!

  10. #10 Murray
    June 21, 2010

    Add my thanks, Psweet! Molt is still a mystery to me!
    Geographic variation between breeding populations?: Does it have something to do with their breeding habitat? Black-tailed,marsh; Hudsonian, taiga; Bar-tailed, tundra; and Marbled, grassland– ?

  11. #11 psweet
    June 22, 2010

    Further clarification, Bardiac. Immature is a rather nebulous term — it would apply to any plumage between the juvenile and the final definitive plumages of adults. It’s worth noting that this definition says nothing of sexual maturity — there are quite a few birds that are able to breed a year or more before they acheive adult plumage (Bald Eagles, for example). Most gull fanatics never use the word immature — the changes from one year to the next are important enough that the term immature doesn’t convey any particularly useful information. On the other hand, we simply distinguish between adult and immature hawks at our hawkwatch — although we do take a stab at aging Bald Eagles to the year, if they come close enough.

  12. #12 Murray
    June 22, 2010

    A quick addendum: “The Hudsonian is considered a near-threatened species. There is an incomplete understanding of its breeding range; population studies are needed.” (From Companion to NGS’s Guide To the Birdsof N.A.-5th Ed.)

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