[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

Austin, Texas

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