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[Fwd: Re: Yellow Grosbeak "bill deformity"]

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  • Thomas Miko
    ... Thomas Miko (Mikó Tamás) thomas.miko@verizon.net thomas_miko@hotmail.com 653 S. Indian Hill Blvd., #C Claremont, CA 91711 U.S.A. 34.109167 N, 117.718293
    Message 1 of 1 , Aug 5, 2006
      >From: Julie Craves <jcraves@...>
      >Date: 2006/08/05 Sat PM 04:42:06 CDT
      >To: Thomas Miko <thomas.miko@...>
      >Subject: Re: Yellow Grosbeak "bill deformity"

      >Hi, Tom.
      >I'm not familiar with molt sequences in tropical grosbeaks, but in
      >Rose-breasted Grosbeaks, immature males (e.g., through their second
      >calendar year, until their second prebasic molt) would have a mix of
      >pale and dark coverts, secondaries, etc. as in this photo:
      >If that's the case with Yellow Grosbeaks, these aren't immature males,
      >negating the young-birds-have-funny-looking-bills theory. I don't
      >believe that it is likely that younger birds have larger lower bills
      >than older birds and "grow" into them. If this is true I believe it
      >would likely occur much sooner in a shorter period of time (first few
      >months of life, if not few weeks). Also, this would sort of imply that
      >you should see a progression in upper bill size from the earliest photos
      >I saw (December 28, 2005) to the latest (March 11, 2006); they seem the
      >same to me.
      >I agree that the lower mandible does look both larger than "normal" and
      >nearly identical in both birds. I'm not sure why you would not consider
      >this a deformity. Not all deformities are severe or debilitating. If
      >one defines a deformity as something outside normal parameters (if this
      >is the case, see below), I would say this qualifies. The odds that two
      >birds would have the same deformity -- and show up in the U.S. -- seems
      >very unlikely to me. This seems to indicate it's the same bird.
      >I don't think it's likely that malnutrition would cause this type of
      >deformity, although I suppose it's possible. Malnutrition does not seem
      >consistent with known causes of bill deformities, unless perhaps there
      >was some sort of contaminant involved. If this is indeed two birds (and
      >there is no subspecific or regional populations that look like this),
      >then it is actually MORE reason to suspect captive origin, because it
      >could mean this is a genetic deformity shared by siblings taken from the
      >same nest, or a brood raised with some sort of contaminated food, or
      >whatever. Again, if this is not a naturally-occurring bill type in a
      >population likely to be vagrant, it is hard to imagine two wild birds
      >with the same deformity arriving in the U.S.
      >It would be more fruitful, I think, to ask people who know more about
      >regional variation in Yellow Grosbeaks, and are familiar with their molt
      >sequences, to first determine whether or not they are the same bird
      >and/or if the bills is indicative of a regional variation, or within
      >normal limits. As these birds wind their way through the records
      >committees, I'm sure experts will be consulted on this topic (I'm no
      >expert on bill deformities, more like an accumulator of data on this
      >Julie A. Craves
      >Rouge River Bird Observatory
      >University of Michigan-Dearborn

      Thomas Miko (Mikó Tamás)


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