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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:
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
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