A numbers game — Pronghorn transplant program on hold after bad year in 2011

IMG 5488“We have to get out of the drought,” said Dr. Louis Harveson of the Borderland Research Institute at Sul Ross State University.

That is the sentiment of a group of researchers involved in moving herds of pronghorn antelope from the Panhandle to the Trans-Pecos region, where numbers have dwindled over the past 20 years from a high of 17.226 animals in 1987 to the current number of 3,745.

The group released 194 animals last year, and watched as the antelope succumbed to disease, predation and starvation due to poor range conditions.

“We started out a little late and just had some really bad luck,” Harveson said. “When we made the decision to relocate in 2010, range conditions were pretty good.”

Harveson said a number of factors contributed to the decline, including parasitic worms, predation by coyotes and bobcats, stress from the move and lack of nutrition. Forty animals were fitted with radio collars, but 26 died within eight weeks of being released. Another 26 fawns were fitted with collars, but only two made it past six months.

“Fawn survival was almost zero across the entire range,” Harveson said. “That is one of the most concerning things because we can’t get numbers up without fawn recruitment. We are wasting our time if no fawns survive.”

Harveson said fawn mortality was the number one indication that vegetation was extremely poor.

“The fawns had body weights that were so far below normal,” he said. “It would be like having a full-term baby that has the weight of a premature baby. Nutrition for the mother is critical, and it just wasn’t there this year.”

Harveson said his team also found a high number of barber pole worms, a parasitic worm, in the transplanted pronghorn — something he also contributes to poor range conditions.

“They were pretty clean when we moved them,” he said. “Within four months, we did fecal tests and found they had ridiculous numbers of worms. We could tell exactly where the pronghorn were concentrated because of the radio collars, and they were concentrated in shallow depressions that held some moisture. Unfortunately, that was also where the worms were concentrated because that is where the forbs were.

“In a wet year, the antelope will spread out and eat everywhere and that will go down.”

Barriers such as fences also prevented pronghorn from traveling to find what little moisture existed.

“From a genetic standpoint, it really isn’t that big of a deal,” Harveson said. “It is a big deal for movement and survival to get to new pastures. We found large clusters of animals in corners of fences they couldn’t cross. We are working with landowners to build pronghorn-friendly fences.”

Harveson said one advantage of the fires last year was the burning of a lot of fences, and landowners have been helpful in replacing old fences with that have an 18-inch gap from the ground and no barbed wire on the lowest strand to allow easier passage.

“We have enough money to move another 200 to 300 animals,” he said. “It is sitting on hold right now waiting for a better time with better range conditions. Maybe next February we’ll release those animals. It’s just a numbers game. The more you can get out there with super stocking, the better chance you have.”