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  1. Re: [CALBIRDS] Fwd: CA RSHA Rapid Territory Abandonment LINK
    DATE: May 5, 2017 @ 3:56pm, 1 year(s) ago
    The status of Red-shouldered Hawk in Santa Clara County is described
    in the Breeding Bird Atlas of Santa Clara County, California.  A
    brief summary is that this hawk was very rare in the county until
    the early 1970s, when numbers increased rapidly.  Using data from
    the Palo Alto and San Jose CBC's that date back to the late 1950s,
    the population increase through 2005 was about 13% a year within the
    Palo Alto count circle and 17% in the San Jose circle.  Both counts
    have had good coverage over the last 50+ years and exceed the 95%
    percentile for party-hours for all United States CBCs.
    We started a summer bird count in the Palo Alto circle in 1981 and
    the summer population increase was less than the winter numbers,
    about 5% a year.  Both the winter and summer increases show a p
    value of less than 0.004.
    Based on Bob Barnes's message, I've looked at the summer numbers
    through 2016.  The population increase is now closer to 3% per year,
    rather than the earlier value of 5% a year.  There has been a
    decline in the total birds counted in the last three summers, but it
    is not clear if this is an artifact of the normal variance of a
    large data series or the start of a changed trend.
    Bill Bousman
    Menlo Park
    On 5/3/2017 4:22 PM, Bob Barnes bbarnes@...
    [CALBIRDS] wrote:
    See below for email message from noted bird guide artisit,
    birder, and
    naturalist John Schmitt re Red-shouldered Hawk 80 to 90
    territory abandonment in SoCal.
    I think it would be good to learn through our observations
    if a decline
    is taking place elsewhere in California as well.
    Serving as the messenger for John Schmitt,
    Bob Barnes, Ridgecrest, Kern County, California
    03MAY17 from John Schmitt...
    Hi Bob,
    I learned of some troubling news about Red-shouldered
    Hawks; I was
    in San Luis Obispo County (Morro Bay, Montana de Oro, San
    Luis Obispo,
    Santa Margarita Valley/ Santa Margarita Lake-all prime
    Hawk localities) on 26 APR leading some friends of mine on
    a short
    birdwatching tour (with a strong emphasis on raptors). We
    failed to either see or hear a single bird. I mentioned
    this to Peter
    Bloom (a well known long time raptor researcher) and his
    response was:
    "I'm not surprised". He went on to relate that there has
    been a severe
    population decline in Orange, Los Angeles, and San Diego
    Counties (80 to
    90 percent territory abandonment in some localities).
    Cause is
    uncertain, but Pete mentioned that some thought
    agrichemicals or West
    Nile Virus may be involved. So I will be taking special
    note of when
    and where I see/hear Red-shouldered here in the (Kern
    River) valley and
    I alert you to perhaps do the same and maybe pass the news
    on to others.
    Good chatting with you.
    Cheers, John
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