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[CALBIRDS] RE: Bird Migration Radar Images

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  • SJPeterson@aol.com
    In a message dated 5/5/2004 12:48:18 AM Mountain Standard Time, CALBIRDS@yahoogroups.com writes: These could be caused by one of three things, clouds, birds or
    Message 1 of 4 , May 5 10:40 AM
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      In a message dated 5/5/2004 12:48:18 AM Mountain Standard Time,
      CALBIRDS@yahoogroups.com writes:
      These could be
      caused by one of three things, clouds, birds or bats.

      Or bugs. NEXRAD is very sensitive and can even show reflectivity from smoke
      (range / forest fires). It's great at picking up evening flights of bugs
      (moths, etc.), especially in the Southeast at night. You'll see a nice "bloom"
      around the radar sites, usually going in the direction of the prevailing winds.
      Check the winds -- if the direction of movement shown on radar (radial
      velocity) is against the prevailing winds, then it's probably something mobile
      enough to proceed against the breeze (birds) and not most bugs (which generally
      flow with the prevaling winds, depending on strength).

      During the daytime, flights of birds can be seen on radar as a "donut" shape
      around the radar shape -- an orangish circle or crescent, depending on whether
      or not the bird "frontal migration" is just approaching the radar or whether
      it is all around the site. This is because the birds generally fly at a given
      altitude range, and since the radar shoots at an angle from the ground, it
      will only start picking up reflectivity from birds a certain distance away from
      the radar site (corresponding to the elevation of the birds). At least this
      is the case over the Gulf of Mexico and slightly inland. I'm not sure how
      birds migrate once far inland...

      Evening flights of moths, (or the evening departure of birds from the ground,
      gaining altitude) show up as a multi-colored "bloom" instead of a donut,
      because of the reflectivity at altitudes from ground-level to much higher. Again,
      prevailing breezes can provide a clue as to whether or not these are birds or
      bugs.

      It's fun stuff to watch, but can be tricky to interpret correctly. It's
      easier to note arrivals off the Gulf of Mexico in spring than it is to observe and
      interpret departures in fall!

      Best,

      --Stacy

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      Stacy Jon Peterson
      4442 Sijan St. Apt. A
      Mtn Home AFB, ID 83648
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