Here are two screen captures from videos I took of the Purple Martin roost along I-35 in Austin in July. (The date is correct but the time stamp is wrong on these images; the videos were recorded at about 9:50 p.m.) These images can't begin to capture the numbers of birds coming to roost or the energy and noise they generate. This was recorded during one of Travis Audubon Society's Purple Martin Party's this year. Estimates of the size of the flock in the roost are upwards of 100,000 PUMA, perhaps double that. Uncountable, really.
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The Purple Martin (Progne subis) is the largest North American swallow. These aerial acrobats have speed and agility in flight, and when approaching their housing, will dive from the sky at great speeds with their wings tucked.