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Arcata Firgatebird

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  • Andrew Engilis
    All -- I had an opportunity to look over the frigatebird photos from Arcata and having spent many years frustratingly working-over frigatebirds in the Pacific,
    Message 1 of 1 , Jul 17, 2007
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      All -- I had an opportunity to look over the frigatebird photos from
      Arcata and having spent many years frustratingly working-over
      frigatebirds in the Pacific, this bird presents some classic problems
      with id. First and foremost, frigatebirds in second cycle plumage
      (which I think this bird may not be) are among the most difficult to
      id and using one or two field characteristics to determine a bird
      should be cautioned; and in many cases birds simply cannot be
      separated to species. Harrison's book does not capture all the
      variance noted for frigatebirds, particularly Pacific Ocean Greaters.

      Determining the age of the bird might be the best way to start, and
      the photos, although inconclusive do give a couple hints. One, the
      bill color. Most first year (Basic 1) frigatebirds (particularly
      juv) have pink bills (at least the basal half, and some
      entire). Most second cycle frigatebirds have grey, bluish-gray, or
      gray-yellowish bills (including lessers), some retain pink
      (females). The pink soft body colors coupled with white head leans
      this bird towards a BAsic 1 bird. Second, primary wear. I believe
      (and I would like to be enlightened if this is an incorrect
      interpretation) that a Basic 1 frigatebird at this time of year would
      have very fresh primaries. Over the course of the next two years of
      frigatebird life, primaries are replaced in a synchronous manner. A
      Basic 2 frigatebird usually shows a very uneven primary pattern
      showing worn feathers being replaced by new feathers, with generally
      the outer primaries being worn and clearly pointed (these are last to
      be replaced at end of molt cycle). The wings of a Basic 2 bird is
      sort of tattered looking with uneven trailing edge. The Arcata bird
      appears to have very fresh primaries (and coverts for that matter)
      and shows no sign of outer primary wear. Thus the bird's molt
      pattern is consistent with a juv or young of the year. Unfortunately
      the wings are very blurry, but one image (no. 6) the upper wing shows
      a very fresh looking set of primaries. Finally, the tail feathers are
      the first to be replaced in a juv frigatebird and so are again, long
      and fresh (This shows well on the photos of the Arcata Bird). A
      Basic II would show tail feather replacement, irregular shape to tail
      and not a long in appeaerance. Based on these characteristics, I
      think the Arcata bird is a young Basic 1 bird (First cycle).

      North Pacific populations of Great Frigatebird can and do show some
      white in the axillaries, which render a spurred look. I have seen
      this on all too many Great Frigatebirds in the Hawaiian Islands, and
      spurs are present on many Magnificent Frigatebirds in Basic 1
      plumage. So my opinion is that the spur, by itself, cannot be used as
      a means to separate frigatebirds at this plumage stage, particularly
      a vagrant. The amount of white on the head and chest of the Arcata
      bird is very consistent with that noted for Great and Magnificent
      Frigatebirds. My experience with Basic 1 Lessers, is that there is a
      fairy extensive rufous wash on the head, but I do not know how
      variable this is. I think the Arcata bird has very little rufous and
      appears white headed. This wash is variable with Greater, with some
      juveniles appearing almost white headed others rusty headed. Many of
      the Hawaii birds are white headed with little wash. The eye ring
      color and bill color do bother me and are inconsistent for
      Magnificent. Both Lesser and Greater Frigatebirds can show pink eye
      rings and bills (particularly juveniles). The white on the
      underparts are variable, but Lessers generally have an arched look,
      kind of like a broad "v", whereas the Greater's tend to have much
      more white down to the belly, imparting a broadened and oval
      appearance. This characteristic is variable based on the exact age
      of the bird, but does impart a different white shape below for Basic
      1 birds. The Arcata Bird seems to have a pattern more consistent
      with Greater.

      This bird remains tough, and based on the age (if I am wrong, which
      could be) and plumage, it is not out of the realm that this bird is a
      Greater Frigatebird and not a Lesser. The shape of white on the
      belly of the Arcata bird seems more consistent for Greater. The head
      is too white (again more Greater-like), and spur is inconclusive. If
      I was to lean one way, I would lean towards it being a Basic 1Greater
      (but am not 100% convinced). I think Magnificent can be ruled out
      based on soft body colors (but I have less experience with
      Mags.). Whatever this bird turns out to be (and be prepared to have
      frigatebird sp as the id), this is a really great find! Thanks for
      the great series of photos.

      Andy Engilis
      Elk Grove



      =====================================================================
      Andrew Engilis, Jr.
      Museum Curator
      Museum of Wildlife and Fish Biology
      Department of Wildlife, Fish, and Conservation Biology
      One Shields Avenue
      University of California, Davis
      Davis, CA 95616

      Phone: (530) 752-0364
      Fax: (530) 752-0364
      E-mail: aengilisjr@...
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