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Three harsh winters and poor fawn production have pronghorn antelope numbers in the state down to about 4,500. There has not been a season on pronghorns since 2009.

It's been three years - the fall of 2008 - since North Dakota has had a pronghorn antelope season. Hunters won't know if there will be a season this fall until after aerial surveys in July, but the numbers going in aren't good.

After three brutal winters going into this year, the last thing the pronghorns needed was another one.

The mild winter North Dakota has been witnessing may be just what the doctor ordered in terms of helping the pronghorn antelope population rebound.

In 2010, the statewide population was estimated at about

6,500 animals. Now it's down to about 4,500.

Since 2003, the pronghorn population had been at or above 10,000, with two of those years pushing 15,000.

Those three nasty winters were the perfect storm.

Heavy snow and cold temperatures led to considerable mortality in adults, and cold, wet springs, especially in the Bowman management region in 2009, led to unprecedented low production, said Bruce Stillings, big game biologist for the North Dakota Game and Fish Department.

In the case of pronghorns, Stillings said, coming up with firm population numbers is easier than it is with mule deer because of the terrain.

Pronghorns are unique among North American big game species. They are not members of the antelope or the goat families, but rather the sole surviving member of a species that dates back 20 million years.

The pronghorn is the only animal in the world to have branched horns and the only animal that sheds its horns as if they were antlers.

Once numbering in the many millions in North America, second only to bison, the pronghorn population has dropped dramatically. It was estimated at about 20,000 by the mid-1920s.

Unlike deer, pronghorns don't jump fences, so they are limited in their movements between winter and summer ranges. Oil development, and in some states, wind energy development, may hamper their movement even more.

The University of Wyoming is in the early stage of a three-year study to track pronghorn behavior on the winter range in the high desert near Medicine Bow in Wyoming.

Nearly 50 animals have been captured and collared. One of the goals is to see if pronghorns will return to areas that have wind farm development or shy away from them.

Most think of the Badlands area and extreme southwestern North Dakota as the prime habitat for pronghorns. While that is true to a large extent, there are smaller pockets around other parts of North Dakota, near Center and the Hazen and Beulah areas.

Stillings said there is no "magic number" that dictates when there are enough animals to reopen the hunting season. He said the state has four pronghorn management areas and each is looked at individually.

"We look at each of the management regions and the hunting units within them," he said.

The biggest factor has been the drop in fawn production over the three previous winters.

Stillings said does older than 1½ years will have twins 98 percent of the time; but that hasn't been the case in recent years.

He said the latest population survey showed a birth rate of

26 fawns per 100 does, the lowest rate documented in the state.

The results of the Wyoming study could give biologists more concrete information on antelope movements between their summer and winter ranges.

One long-held belief is that when pronghorns vacate an area for whatever reason, they don't return.

Stillings said it's something he's worried about, given the amount of the oil exploration activity in western North Dakota.

A radio collar study in 2004 showed that antelope in North Dakota traveled as far as 120 miles to find a suitable winter range.

One animal eventually ended up in Wyoming. But Stillings said the study also showed that 99 percent of the time, the pronghorns returned to their summer range.

Fences and interstate highways are just two man-made obstructions pronghorns shy away from, Stillings said.

The 2004 study showed bands of pronghorns are three times more likely to settle into a summer area that is at least a mile from the nearest road, he said.

Stillings said it's not just oil wells that are an issue, but other things like roads and traffic in the West that may impact the population.

"It's a huge concern," he said. "Antelope need that open landscape and do best in areas that are free of disturbance."

The good news, Stilling said, is that as favorable as the weather has been this winter, it was equally favorable this spring and summer - and hopefully that will help the reproductive success of the pronghorns.

During the tough winters, the animals were stressed physically, which hurt reproduction.

Going into this fall, Stillings said, the animals were in better condition physically and could tolerate more disturbances in their routine.

"Going into the winter, they were in excellent conditions, and that's good news," Stillings said.

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Reach reporter Brian Gehring 250-8254 or brian.gehring@bismarcktribune.com.

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