[texbirds] NEXRAD radar images of Purple Martin roosts
- From: "John Arvin" <jarvin@xxxxxxxx>
- To: "New Texbirds" <texbirds@xxxxxxxxxxxxx>
- Date: Sun, 1 Jul 2012 11:53:50 -0500
This morning the National Weather Service page for Central Texas was
displaying the NEXRAD radar image because there were showers in the area.
The image was animated which is done by displaying the 10-12 still images
for the previous hour in rapid sequence just like frames in movie film. So
I was watching the image that began at 6:00 a.m. and ended with the present
image at 7:00. There were giant Purple Martin "roost rings" visible just
WSW of the outer loop in San Antonio and one over the center of Austin,
presumably the Highland Mall roost. These roost images begin as small tight
circles that enlarge and eventually become diffuse at the end of the
sequence. If you check around sunset you can see similar ring open like
kernels of popcorn beginning at San Antonio and Austin (the Congress Ave.
bridge colony and then spread westward across the Hill Country as tens of
millions of Mexican Free-tailed Bats exist their caves. This is best viewed
on clear evenings.
So if you can't get over to those martin roosts at the proper time to see
them form in the evening or disperse in the morning you can watch it on any
NEXRAD radar outlet on the internet if you tune in just before 7:00 a.m.
Of interest is an almost adult-plumaged Broad-winged Hawk which has been
perched on top of a telephone pole across the street drying its plumage
from the light shower we had earlier and preening. It is molting and small
body feathers are regularly seen floating off in the breeze. It has been at
it for the past half hour. I saw an adult bird overhead a few days ago and
this is obviously a different individual. At least its presence has a
dampening affect on the incredibly dense White-winged Dove population.
John C. Arvin
Research Associate
Gulf Coast Bird Observatory
103 West Hwy 332
Lake Jackson, TX 77566
jarvin@xxxxxxxx
www.gcbo.org
Austin, Texas
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