Wednesday, July 17, 2013

Purple Martin radar images

Can you believe that our Purple Martin roost is visible on radar?  You have to go to a website with unfiltered radar, such as  You can also pick out other roosts scattered around the Southeast.

Below are images from this morning, first the Slidell and then the Mobile radars.

The above image is the Slidell site.  The main light blue blob is meaningless scatter near the radar installation. The blobs at the north and south end of the Causeway are the departing martins a few minutes before 6 AM.  There appear to be more at the north end of the bridge than the south end, though there may be an effect of being a bit closer to the radar so the beam is lower and catches more birds.  You may have noticed that the north end of the bridge has martin fences to avoid car impacts, just like the south end- but farther from shore.

The Mobile radar actually shows five apparent roosts, four of them onshore encircling the hub of near-installation scatter, showing up as commas (the radar is probably just picking up a portion of an expanding ring of birds).  If you look closely, there is another comma partially hidden within the central scatter that appears to be leaving a roost near or on Dauphin Island; it looks darker blue than the scatter.  This is a mystery, since some of the birds appear to be headed out to sea- unlikely for martins, I would think.


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