MESONET TICKER ... MESONET TICKER ... MESONET TICKER ... MESONET TICKER ... August 11, 2005 August 11, 2005 August 11, 2005 August 11, 2005
Diagnosis: Avian Flew
This week's Tickers made the biology circuit and the consensus expert opinion: the bird-rings were made by large seasonal colonies of purple martins.
These birds actually exhibit the behavior that puzzled the Ticker Staff. They amass in huge quanitites over night, then shortly before sunrise, they take off en masse in a near-symmetric pattern in all directions (which explains the near-perfect expanding rings).
It seems that a couple of factors cooperated to bring us our ringed, winged radar show:
First of all, the refraction of the radar beam allowed us to see nearer the surface than usual. Second, purple martins don't always hang out in giant communal roosts. Most of their time in North America, they live and nest in smaller social units, such as the familiar purple martin houses you'll see in urbs and suburbs. Only in the weeks just before their annual migration back to South America do they cluster in roosts that can number into the hundreds of thousands (apparently there's some sort of biological groups discount on intercontinental travel).
Recall one of our images from Monday morning: http://ticker.mesonet.org/archive/20050808/0645.png
The rings over Tulsa and just northwest of Hot Springs are large, well-known colonies of purple martins: an urban colony in Tulsa, and a laid-back country community on Lake Ouachita. The other rings are almost certainly purple martins, as they are near the edges of lakes.
Thanks to the dozens of folks who offered purple martin advice over the last 24 hours, especially the folks at the Purple Martin Conservation Association at Edinborough (PA) University. You can read all about martin roosting and other behavior at their excellent website: http://www.purplemartin.org/
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