Purple Martin Roost Rings on Radar

Going to your local premigratory roosts are a great way to herald the end of summer. The spectacular swarms of purple martins, descending in on trees, weighing down their branches like a heavy burden as countless more rain down to jockey for a spot  for the night. It is an awe inspiring sight not easily forgotten.

What happens to all those birds in the morning though? Not many people hang around or get up early enough to watch the birds ascend to the sky come sunrise.¬† The National Weather Service and their Doppler Radars have documented this phenomenon for years since bird movements were discovered on radar back in the 1940’s. On the radar image here, you can see the red arrows pointing to these radar rings (also called doughnuts) formed by the mass of birds flying out and away from the roosting sites. According to the Purple Martin Conservation Association and their Project Martin Roost, more than 300 possible roosts occur in Eastern North America. The largest known roost, at Lake Murray in South Carolina has over 700,000 birds.

Kevin R. Russell and Sidney A. Gauthreaux, jr. did a wonderful study titled, Use of Weather Radar to Characterize Movements of Roosting Purple Martins, (back in 1998) that is an interesting read. You can also read what the National Weather Service has to say about it with their article titled Roosting Birds Detected on NWS Doppler Radar.

If you know of a roost consider visiting one before the martins are gone. You won’t regret it. If you can’t get to one you can always watch our video we took in 2009 of a local roost in Davie Florida here.

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