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Re: [CALBIRDS] Island Scrub-Jay movements question

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  • Jeff Davis
    The paper I cited earlier was an old one. Paul is right about the more current view of Pleistocene bathymetry. And apparently there was a record of Western
    Message 1 of 4 , Oct 1, 2002
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      The paper I cited earlier was an old one. Paul is right about the
      more current view of Pleistocene bathymetry. And apparently there
      was a record of Western Scrub-Jay from the Farallones. But Ned
      Johnson, in the same 1972 paper I cited before, considered the bird
      to be human assisted. Pyle and Henderson (WESTERN BIRDS 22:41-84) do
      not even mention it in their 1991 summary of occurrence patterns of
      SE Farallon birds. In a nice overview in BIRDING (29:476-485; 1997),
      Atwood and Collins suggest the most plausible explanation for the
      presence of the jay on Santa Cruz Island is overwater flight. During
      the late Pleistocene this distance would have been as little as 4
      miles. But, apparently, available molecular data cannot be used to
      determine time of divergence with other Aphelocoma jays. Therefore
      the approximate time of its arrival on the island is not known. The
      origin of slender salamanders and a night lizard on some of the
      islands is mysterious. Schoenherr, Feldmeth, and Emerson (Natural
      History of the Islands of California, UC Press, 1999) suggest they
      may have arrived by vacariant transport, associated with plate
      tectonics. In the Miocene the northern islands may have been
      connected to the mainland much farther south, but slid northward
      along fault systems to their present location. Although overwater
      flight during the Pleistocene seems a more likely hypothesis for the
      jay's island origin than vacariance during the Miocene, perhaps the
      latter cannot be ruled out.

      Jeff Davis
      Fresno, CA


      At 00:21 -0700 10/2/02, Paul Keller wrote:
      >My take on the Island Scrub-Jay is different than that of Jeff Davis, though
      >not being any expert I acknowledge that Jeff's account may be more accurate
      >than mine. Anyway, here goes.
      >Minimum sea level during the Ice Age was about 120m lower than today's
      >which, given modern bathymetric data, is insufficient to expose a land
      >connection to any of the Channel Is. It would, however, result in Anacapa,
      >Santa Cruz I., Santa Rosa I. And San Miguel I. being connected into one
      >large island called Santa Rosae which lay only a few kilometers from the
      >mainland. Therefore ancestral scrub jays must have crossed at least such a
      >water barrier. Perhaps a warm dry spell between the melting of the ice
      >about 12000 years ago (and the restoration of current sea level) and today
      >exterminated the jays from all the northern Channel Is. except Santa Cruz I.
      >I thought that there was indeed a record of a Western Scrub-jay on the
      >Farralon Is. Is there any expert with access to such records that can
      >clarify this issue? Jeff, if you are such an expert, my apologies.
      >My hope is that there's continued discussion about the Island-Scrub-Jay
      >distribution question, a question that has piqued my curiosity for some
      >time.

      --
    • Paul Keller
      On 02/10/01 08:41 AM, Nathan Hentze wrote: My take on the Island Scrub-Jay is different than that of Jeff Davis, though not being any
      Message 2 of 4 , Oct 2, 2002
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        On 02/10/01 08:41 AM, "Nathan Hentze" <w_tanager@...> wrote:

        My take on the Island Scrub-Jay is different than that of Jeff Davis, though
        not being any expert I acknowledge that Jeff's account may be more accurate
        than mine. Anyway, here goes.
        Minimum sea level during the Ice Age was about 120m lower than today's
        which, given modern bathymetric data, is insufficient to expose a land
        connection to any of the Channel Is. It would, however, result in Anacapa,
        Santa Cruz I., Santa Rosa I. And San Miguel I. being connected into one
        large island called Santa Rosae which lay only a few kilometers from the
        mainland. Therefore ancestral scrub jays must have crossed at least such a
        water barrier. Perhaps a warm dry spell between the melting of the ice
        about 12000 years ago (and the restoration of current sea level) and today
        exterminated the jays from all the northern Channel Is. except Santa Cruz I.
        I thought that there was indeed a record of a Western Scrub-jay on the
        Farralon Is. Is there any expert with access to such records that can
        clarify this issue? Jeff, if you are such an expert, my apologies.
        My hope is that there's continued discussion about the Island-Scrub-Jay
        distribution question, a question that has piqued my curiosity for some
        time. -- Paul Keller, Goleta SBA

        > Hello California birders,
        >
        > Up in the Pac. NW we've been experiencing a steady Western Scrub-Jay
        > northward expansion in recent years. I was wondering how much of a
        > barrier water is to scrub jays, and whether one would be likely to
        > island hop, or fly directly across one of the straits to reach
        > Vancouver Island. This led me to consider the Island Scrub-Jay, so I
        > am asking if an Island Scrub has ever been recorded on any of the
        > other Channel islands (ie., Anacapa, Santa Rosa), and what the
        > distance involved between Santa Cruz Island and the closest other
        > islands would be. Thanks very much for any answers regarding the
        > Island Scrub, or if anyone knows if water is at all a major barrier
        > to Westerns.
        >
        > You can reply off list if you want, to
        > w_tanager@ hotmail.com
        >
        > Nathan Hentze,
        > Cumberland, BC, Canada
        >
        >
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