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Fwd: Corvids & West Nile

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  • Stephen Long
    Message 1 of 2 , Apr 1 12:13 PM
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      >CALBIRDERS,
      >
      >This year, we birders on the left coast should begin to see some
      >drastic reductions in Corvids due to West Nile Virus. A "Short
      >Communication" in the February, 2005 Condor, entitled: "West Nile
      >Virus Devastates an American Crow Population" (by Carolee Caffrey,
      >et al.), documents what happened to a well-studied, color-marked
      >population of crows in Stillwater, OK when WNV showed up. The
      >pathogen causes very nearly 100% mortality in infected individuals,
      >echoing the experience of American Native Peoples encountering a
      >"new" pathogen for which they had virtually no immunity (smallpox).
      >
      >West Nile arrived in the geographic area of the study population in
      >June 2003. By the end of the year, 65% of the study population had
      >died (2 out of every 3 birds), and the mortality amongst fledglings
      >was a whopping 82%. This compares to pre-WNV mortality levels of 2%
      >of adults & 34% for fledglings.
      >
      >Although the authors were careful to point out that their study was
      >confined to a single corvid species, it is not unreasonable to
      >predict similiar devastation to at least congeners of the American
      >Crow, if not the entire Family of Corvidae in North America. Which
      >brings us to California, where birders have for several years been
      >reporting an increase in Corvus populations -- that trend is now
      >likely to show a sudden and precipitous reversal.
      >
      >Frankly, I'm not too worried that crows and ravens are going to
      >disappear from the California avifauna. But I do admit to some
      >concern over the low-population endemic Corvid of California, the
      >Island Scrub-Jay. Other birders and ornithologists will have much
      >more information than I about the threat to this taxon, e.g. is
      >there sufficient breeding habitat for mosquitoes? I'd be interested
      >in hearing from others.
      >
      >While there is virtually no data on what constitutes the WNV
      >"season" in California, it would not be unreasonable to assume that
      >it mirrors the season elsewhere in North America, namely
      >June-October. So by this year's Christmas Bird Counts, we should
      >begin to have an idea if the California corvid populations are
      >declining.
      >
      >Knowing my own birding disposition with regard to crows & ravens --
      >see the first one of a day, then ignore all the rest -- I've had to
      >discipline myself to begin to count them. Birding just became a
      >richer activity!
      >
      >Regards,
      >Stephen M. Long
      >Museum of Vertebrate Zoology
      >University of California
      >Berkeley, CA 94720
      >Telephone: 510-642-8299
      >Telefax: 510-643-8238
    • Paul Jorgensen
      Hawk counters (Hal Cohen and others) have tallied over 1200 Common Ravens coming to an evening roost on Borrego Valley Road, Borrego Springs, Ca., on one
      Message 2 of 2 , Apr 1 1:25 PM
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        Hawk counters (Hal Cohen and others) have tallied over 1200 Common
        Ravens coming to an evening roost on Borrego Valley Road, Borrego
        Springs, Ca., on one evening, each of the last two years in spring. The
        roost is a large stand, perhaps several hundred acres of palms,
        eucalyptus and tamarisk, located 1.4 miles north of County S-22. These
        numbers were counted as ravens came into the east and north side of the
        roost only, and thus likely represent some fraction of the valley's
        population!

        A thinning of corvids by the predicted arrival of WNV will be watched
        for and might be beneficial to its prey, especially nesting birds.
        Unfortunately, we only keep the official daily hawkwatch each year from
        early Feb to mid April but, we will be on the lookout for changes in
        raven numbers. Most observers agree that the raven population here is at
        an all-time high.

        ________________________
        Paul Jorgensen
        California State Parks
        Colorado Desert District
        200 Palm Canyon Drive
        Borrego Springs, CA 92004
        phone: (760) 767-5748
        email: pjorgensen@...
        _______________________


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