Sunday, August 15, 2010

"Roost Rings"

An eight-image animation of base reflectivity, starting at 6:12 AM and ending at 7:36 AM, August 2.

I wake up- the first thing I typically do is take a look outside to get a feel for the weather.  Cloudy- no wind, and no precipitation.  Is it going to rain today?

Recently, I've been visiting the website of the National Weather Service Forecast Office in Wilmington Ohio, for my daily weather predictions.  I particularly enjoy the area forecast discussion. You get a feel for just how much room for error is built into our daily forecasts.

But this morning, something new caught my eye.  A link titled "Roosting Birds Detected on NWS Doppler Radar".  After a quick click I was led to several animated radar maps showing expanding doughnut shaped patterns around NWS radar sites.  According to the NWS, the radar is recording the pattern of birds flying away from their roosts at dawn.  And they postulate that these birds are most likely purple martins.

At first, I questioned the doughnut pattern- why does it look like all the birds are radiating out from each station?  The meteorologist explains this by saying "The unique doughnut pattern of these roost rings is the result of the martins departing their roosting site in all directions, roughly in equal densities".  That doesn't explain the pattern to me, but he is saying that the pattern tells them that the birds are radiating out in all directions.  One last very interesting tidbit of information- in the map above, the author points out how the doughnuts begin first in the east, then gradually move west, corresponding with the rising sun. Pretty cool, eh?



  1. Tom, if the tiny black dots in the centers of the radar blobs are the radar locations, then it makes sense that the expanding circular waves are peripheral to the blobs because the birds are not at the radar sites. Of course, it also would work only for mass roosting birds. Betcha this fall the blackbirds will add doughnuts. Wonder if similar can be seen for heronries in the nesting season and vulture roosts in summer?

    That graphic is sooooo cool! Now I'm gonna go see if there's one a little more local to me than Ohio!

    Thanks, guy!

  2. Amazing gif.
    I have tried finding these using our local radar in South FLA but never had any luck.

  3. Just checked - nope for Jax, either.

  4. Very cool :)

    More details can be found at the "How NEXRAD Works" pages run by Clemson University Radar Ornithology Laboratory (CUROL).

    Here's their page on roost rings.