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RE: [CALBIRDS] Bird Migration Radar Images

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  • Jim Gain
    I am not an expert in this, but I did sleep in a Holiday Inn last night... Just kidding. I have received several emails asking for more clarification about the
    Message 1 of 4 , May 4, 2004
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      I am not an expert in this, but I did sleep in a Holiday Inn last night...
      Just kidding. I have received several emails asking for more clarification
      about the radar images. My school Internet was shut down today because of
      the worm going around so I couldn't respond until now. I only know a little
      about this phenomenon. If you go to the site below and click on one of the
      sites in California, you will get an image with lots of cloud-like
      formations. You shouldn't have to change any of the settings. These could be
      caused by one of three things, clouds, birds or bats. On a cloudless
      evening, you can rule out the clouds. If you click on the image, you get a
      second image that shows the relative movement of whatever the radar is
      picking up. Blue indicates movement towards the radar and orange indicates
      movement away from the radar. The images this morning clearly indicated a
      northward movement. So that should indicate that it would be a large
      movement of birds, not bats. I just checked the area over Hanford and it
      shows a mixed cloud, without much uniform direction. When I then checked the
      area over Brownsville TX (in darkness right now) the migration had begun. I
      guess the birds start heading northward right before or shortly after
      sunset. I would check it out starting around 8 or 8:30 this evening and see
      how the clouds of migrants move north during the evening.

      Again, I only know a little about this and am mostly passing along what I
      followed on TexBirds.

      Jim Gain
      Modesto

      -----Original Message-----
      From: Jim Gain [mailto:sta-birder@...]
      Sent: Tuesday, May 04, 2004 5:36 AM
      To: central_valley_birds@yahoogroups.com; CALBIRDS@yahoogroups.com
      Subject: [CALBIRDS] Bird Migration Radar Images

      I have been following the TexBirds email last night about a massive bird
      liftoff during the night that they have been following on the NEXRAD
      website. So, naturally curious to see how it looked over the valley, I
      checked it out. WOW

      There is a huge flight of birds over the central valley right now. I started
      checking from the San Diego area and moved north. There is only a little
      movement right now down south, but by the time you look at the Fresno area,
      the radar screen is full.

      Go to http://www.rap.ucar.edu/weather/radar/ and click on an area, then
      click on the image to see the direction of the flocks. They are moving due
      north.



      Jim Gain

      Modesto



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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 2 of 4 , May 5, 2004
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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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