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Re: crecca/carolinensis GW Teal comments (longish)

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  • Les Chibana
    The male Eurasian Green-winged Teal that we saw on 17 Nov had well- developed white horizontal scapular bars. I thought that there might have been a second
    Message 1 of 2 , Nov 23, 2002
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      The male Eurasian Green-winged Teal that we saw on 17 Nov had well-
      developed white horizontal scapular bars. I thought that there might
      have been a second individual that was still in mid-molt. But since
      our second, third and fourth scans through the flock failed to turn
      up another crecca, I didn't mention the possibility of that one. I'm
      not sure if we did see the bird that Don described in his post, but
      the one we did see was a very clearly marked male crecca no apparent
      incomplete molt. I think that there's a 7th MTY record in the area.

      Les
      --
      Les Chibana
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      On Saturday, November 23, 2002 6:13 PM, creagrus@... wrote:
      >Last Sunday (17 Nov), Les Chibana and group reported a male Eurasian
      >Green-winged Teal (A. c. crecca) from pond 1 at Moonglow Dairy. This is
      >just the 6th MTY record, but beyond the report I heard no discussion of
      >the bird. What is presumably the same male was present again today on
      >pond 1 at Moonglow, and viewed by several of us, including Rita
      >Carratello and Rick Fournier. Although it lacked the white shoulder bar
      >of American Green-winged Teal (A.c. carolinensis), we were all surprised
      >to see that it also lack the prominent, white scapular stripe of male
      >crecca, and therefore we studied the bird in detail. This taxa is
      >interesting for several reasons, and perhaps chief of among them is the
      >fact that the British Ornithologists’ Union split crecca from
      >carolinensis recently, and that the AOU may follow in due course. This
      >would mean crecca would again revert to the separate species it was when
      >I first started birding, when it was known in America as
      >“Common Teal.”
      >
      >We had numerous, unhurried opportunities to study it adjacent to a
      >variety of male American GW Teal (there were ~50 carolinensis present).
      >My field notes list these differences:
      >1) no hint of white shoulder bar, and underparts otherwise seem
      >completely molted in
      >2) facial pattern different, with buffy edge to green ear-patch broader
      >and extending forward as a curving line all the way to the bill
      >3) when it flapped its wings, green speculum bordered anteriorly but
      >broad white (not buffy) bar, and this bar slightly wedge-shaped, being
      >broadest away from the body
      >4) slightly rougher or granier vermiculations to gray sides (seen only
      >in some lights)
      >5) thin white bar anterior to black bar on flanks (but this was matched
      >by a few, but not most, carolinensis)
      >6) very slightly larger size and looked heavier, carried itself
      >‘heavier’ on the water
      >7) good side-by-side profile views showed it had a longer and somewhat
      >heftier bill
      >8) tertials crisply edged with black and then white, giving a patterned
      >look, while carolinensis lacked white edgings to tertials
      >9) barest hint of dull, small white spots where the scapular bar would
      >be expected
      >
      >Except for the lack of scapular stripe, nothing suggested hybridization
      >or introgression with carolinensis, and the longer bill and slightly
      >larger size was consistent with a different population than
      >carolinensis.
      >
      >I have now done a bit of research, and can answer the question: ‘why
      >doesn’t it have a white scapular stripe like all the field guides show?’
      >I quote from Palmer (1976) Handbook of N. Amer. Birds, Vol. 2: “Drakes
      >commonly do not molt back into Alternate head-body until well along in
      >fall. During this period of molting, the feathering on sides of breast
      >(with or without a white bar [depending on continent]) typically is
      >fully developed for a considerable time (up to several weeks?) before
      >the long scapulars grow. These scapulars are the last of the incoming
      >Alternate feathers and often they are not fully grown until very late
      >Nov. or sometimes as late as in Jan. ... Thus the period when all
      >characteristics of drake body feathering that are useful afield in
      >distinguishing crecca (and possible nimia) from carolinensis, or in
      >recognizing individuals having mixed characteristics, extends only from
      >about Dec. into the following summer.”
      >
      >The answer thus is: the scapulars with the white stripe haven’t grown in
      >yet’ (but the small white dots we saw are likely them starting the
      >grow).
      >
      >Note that Palmer mentions the race “nimia.” So does Bellrose’s older
      >text on waterfowl. This is the population that is said to be resident on
      >the outer Aleutian Island. It was said to be slightly larger than
      >nominate crecca, which nests across all of northern Eurasia out to NE
      >Siberia. Birds of the Western Palearctic (Cramp & Simmons 1977) does not
      >recognize nimia. Rather, they report that NE Asia crecca population
      >average larger than western Asia and European populations, and also
      >larger than any population of carolinensis. The longer bill and slightly
      >larger size of the Moonglow bird is consistent with a bird from
      >NE Asia.
      >
      >Madge & Burn’s (1988) Waterfowl accepts nimia, somewhat tenuously, but
      >doesn’t add anything more. Grinnell & Miller (1944) assign ‘Common Teal’
      >to an appendix of birds that need further confirmation, and do not
      >mention nimia. I rather suspect that BWP represents the more modern
      >view, and that ‘nimia’ is not diagnosable and thus not a good subspecies
      >(see Patten & Unitt, 2002, ‘Diagnosability versus mean differences of
      >Sag Sparrow subspecies, Auk 119:911-923).
      >
      >I didn’t know about the molt schedule of male GW Teals, or about the
      >‘nimia’ subspecies before, so it was a good learning experience
      >for me.
      >
      >A final note: we had a Sibley with us, but it was misleading in some
      >respects. First, obviously, it didn't discuss the critical molt
      >schedule. Second, it suggested that crecca has a broad bar anterior to
      >the black flank bar, and that carolinensis lacks this. Actually, we
      >found a few carolinensis that had a sliver of this bar (as did this
      >bird) but BWP paints both with similar pattern, and does not recognize
      >any distiinction on this point (nor does Palmer). Sibley did note that
      >NE Asian populations are larger but did not talk about the longer bill.
      >Differences in vermiculation on the sides was not as pronouned as Sibley
      >showed. Over-reliance on Sibley -- or any field guide that has no room
      >to discuss all these topics (we later checked Nat'l Geo, which was also
      >of no help in this instance) -- could surely lead to mistaken results.
      >This again emphasizes the need to check literature that is much more
      >thorough than field guides can possibly offer. The 'family' book (Madge
      >& Burn) was quite disappointing on this topic, and didn't get to
      >answers. It took handbooks like Palmer and BWP to address these more
      >detailed -- and perhaps more interesting -- topics.
      >
      >Don Roberson
      >Pacific Grove CA
      >36°38’N, 121°58’W
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