A pronghorn antelope is released from a trailer on February 23, 2011, at the East Hip-O Ranch west of Marfa. While the population decline here remains a mystery, biologists are studying factors including drought, hard winters, an internal parasite called the barber pole worm, predation and reduction of open range by net wire fences. Photo: John Davenport/jdavenport@express-news.net / jdavenport@express-news.net
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