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Texas Parks & Wildlife Department, Earl Nottingham, File, Associated Press
FILE - In this Feb. 23, 2011 file photo provided by the Texas Parks & Wildlife Department, pronghorn antelopes are prepared for release to their new home by Jason Wagner with Texas Parks & Wildlife, left, and Miguel Grageda, Sul Ross State University student, right, near Marfa, Texas. Researchers studying what has caused pronghorn in West Texas to die off will wait until next year to relocate more of the animals to the area because the ongoing drought complicates efforts to replenish the number of animals. Sul Ross State University in Alpine and the Texas Parks and Wildlife Department are sharing results of their efforts to determine what's causing the drop in numbers.

DALLAS — Researchers studying the decline of the pronghorn population in West Texas will wait until at least next year to relocate more of the animals to the area because of the ongoing drought.

"We will not make any headway until that drought is reversed," said Louis Harveson, director of the Borderlands Research Institute for Natural Resource Management at Sul Ross State University in Alpine. The institute is working with the Texas Parks and Wildlife Department to study the drop.

Researchers had hoped that studying pronghorn transplanted last spring from the Panhandle — where there's a thriving population — would both bolster the population and provide some clues about what was wrong among West Texas pronghorn.

But a year of harsh conditions including freezes, drought, extreme heat and wildfires took a toll on the research. Harveson said once rains to return to the area, researchers are hopeful they can bring around 500 of the animals to the area.

Pronghorn have a body type somewhat like a deer, with distinctive white stripes on their faces and necks and white markings that come halfway up their sides.

In the mid-1980s, West Texas had about 17,000 of the animals, but since then the population has mostly been on the decline to a 30-year low of 3,745 animals recorded last year. Researchers say that while the animals have been affected by drought at times, that alone can't explain the decline.

For instance, following drought in the 1990s, pronghorn populations showed an initial recovery before continuing a decline even after good rainfalls.

Among possible culprits is a type of parasitic worm that has been found in high numbers in West Texas pronghorn. But it is possible the worms are simply taking advantage of pronghorn weakened by something else.

Eighty of the about 200 pronghorn that were transplanted to West Texas in February 2011 were fitted with radio collars. Of those, 63 died: 11 died in transport or from effects of the transport; 15 were killed by predators; two were killed by vehicles; two died from the parasitic worm and 33 died of unknown causes.

Harveson said it's often hard to determine the cause of death if they don't get to the body soon enough because of the damage done by animals eating the carcass.

Among the early findings of researchers is that pronghorn are not able to get around fences to find better food or escape predators, which may have contributed to several deaths. Pronghorn are reluctant to jump fences, so a pronghorn-friendly fence would be far enough off the ground for them to squeeze under.

"We're not out of the woods. We still have a long road ahead of us," Harveson said. "We're hoping everyone won't give up on the pronghorn."