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Aging and Sexing the Solano Co. Snowy Owl

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  • Dave Quady
    Birders: Prior to seeing the bird on Saturday, January 14, I reviewed Josephson s key (Bertie Josephson (1980). Aging and Sexing Snowy Owls, J. Field
    Message 1 of 1 , Feb 6, 2006
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      Birders:

      Prior to seeing the bird on Saturday, January 14, I reviewed
      Josephson's key (Bertie Josephson (1980). Aging and Sexing Snowy Owls,
      J. Field Ornithol., 51:149-160 (1980)), and tried to apply it as I
      looked at the bird. I concluded that the bird was an adult female
      (after hatch year, at least), relying on impressions that the bird's
      barring was fairly extensive and bold, but that there was not extensive
      mottling on its coverts.

      At the time Josephson wrote, he was unsure whether Snowy Owls displayed
      more than one definitive basic plumage. Much has been learned since
      then, including how this species replaces secondaries and primaries as
      it ages; see Peter Pyle's 1997 Identification Guide to North American
      Birds, Part I ("IDG", for short). I had access to a few flight shots
      that I thought might let me apply Pyle's guide: Bob Lewis's fairly
      close shot of the bird's underwing (showing all its primaries and about
      half its secondaries), and his and Steve Hampton's more distant shots
      that showed the undersides of both wings, In these photos it appeared
      that all the bird's flight feathers were of an even age, pointing me
      toward an after hatch year (probably second year (SY)) bird; I still
      thought it was a female.

      Peter Pyle was kind enough to review my thinking. Here are excerpts
      from his emails;

      "I looked at Keith Hansen's video of it a week or so ago and concluded
      SY male. Looking at the image you sent (especially the open-wing shot)
      I still would go with this. My strategy with these is to age them first
      and then sex them, as the ageing criteria are reliant on molt patterns
      and less subject to individual variation than the plumage criteria
      (number and thickness of bars on various feathers). On the open wing
      shot, note that all of the bars line up evenly (as you noticed) and
      that all of the primaries and secondaries appear to be of the same
      generation. Post-juvenal primaries and secondaries would not only [be]
      thicker and glossier but they'd show bars in a very different pattern
      (generally fewer) that do not line up with the rest.

      "P7 is the longest feather and gets the most exposure, which is why it
      looks a bit more worn than p8-p10, among which there is a natural wear
      cline. Note also that all outer primaries are narrow at the tip. So
      based on this I'm happy it was an SY, and then the patterns shown in
      Fig. 50 of the IDG (p. 80) and other features (lack of real heavy
      barring to the body, etc.) indicate male over female. As far as bar
      patterns there is substantial overlap between SY male and ASY female so
      it is generally not safe to rely strictly on this.

      "SY females generally have much heavier barring than the Solano bird.

      "Females also seem bulkier to me, not just longer in dimensions. The
      Solano bird appeared more stream-lined, like a male. I was able to see
      the scapulars and central rectrices on Keith's video and they were a
      good match for HY/SY male in Figure 50 of the IDG, nowhere near as dark
      as the HY/SY female. I think I chose these feathers as the most
      diagnostic, but all tracts probably show at least average differences
      between the age-sex groups, including the primaries and secondaries.
      Without looking at specimens again I would be unable to comment on the
      bar-pattern on the remiges of the Solano bird but would also bet they
      favor male among SYs.

      "Also of note, I've looked at age and sex of other Snowy Owls that
      reached California (particularly during the 1973-1974 incursion) and I
      think almost all (if not all) that I could properly judge were HY/SYs.

      "Hope this helps and by all means feel free to pass this stuff on."

      It sure does help -- me, at least; thanks, Peter! I have seen too few
      Snowy Owls in life, and I clearly didn't spend enough time trying to
      age and sex the ones I've looked through in museum trays. Maybe I can
      do better with the next one I encounter.

      And here's hoping another one appears in California soon!

      Dave Quady
      Berkeley, California
      davequady@...
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