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Bird Migration Radar Images

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  • Jim Gain
    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,
    Message 1 of 4 , May 4, 2004
      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



      [Non-text portions of this message have been removed]
    • Al Eisner
      ... Jim: These plots look interesting, but forgive some naive questions. First, how does one tell that these are birds one is seeing? Second, how does one
      Message 2 of 4 , May 4, 2004
        On Tue, 4 May 2004, Jim Gain wrote:

        > 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:
        These plots look interesting, but forgive some naive questions. First,
        how does one tell that these are birds one is seeing? Second, how does one
        get a direction (such as "due north") from a one-dimensional color scale?
        (Direction somehow needs to be two-dimensional.)
        Thanks, Al Eisner
      • 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 3 of 4 , May 4, 2004
          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



          [Non-text portions of this message have been removed]



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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 4 of 4 , May 5, 2004
            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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