Biologists study pronghorn migration in era of fragmentation

Pronghorns captured and fitted with GPS collars in northern Montana and Canada have provided a wealth of data for wildlife biologists.

For 30,000 years pronghorns have migrated in the fall and winter as they sought out the best places to find nutritious food, give birth, raise their fawns and survive brutal cold, snow, drought and predators.

This wisdom has allowed the 120-pound animals, also known as antelope, to survive while other animals like the dire wolf and giant sloths went extinct.

A recently published study gives greater insight into why and where a collection of GPS-collared pronghorns traveled as they moved between Canada and Montana. Such data will be essential if humans want to help pronghorns survive.

“The study is really the first assessment of … what kind of habitat is important while they are migrating,” said Andrew Jakes, a wildlife biologist for the National Wildlife Federation, who led the most recent study that was published in the scientific journal PLOS ONE.

“What this research has highlighted is how pronghorn are indicative of how wildlife try to edge out a living on a highly fragmented landscape and that jurisdictional boundaries are just lines on a piece of paper,” said Paul Jones, senior wildlife biologist for Alberta Conservation Association, one of the study participants. “It also shows that pronghorn at the northern periphery of their range are sitting on the edge of a precipice ready to fall off if we lose these migration routes.”

Study

The six-year study net-gunned 185 pronghorns from helicopters and fitted them with GPS collars. Out of that total, 94 pronghorns migrated between Alberta, Saskatchewan and Montana. Another 76 were classified as nonmigratory residents, and some collars were never recovered.

“The big thing with Andrew’s study … is that you get really detailed information,” said John Carlson, branch chief of Resources and Science for the Bureau of Land Management.

The information showed pronghorn movements are “much more dynamic in space and time than we realized,” he said.

For example, one of the collared animals walked from southern Valley County across the ice on Fort Peck Reservoir before being struck and killed by a vehicle near Jordan. It was a behavior and distance unknown to wildlife biologists until being revealed by a collared animal. Another pronghorn ran 15 to 20 miles down Highway 2 for six hours during a blizzard when the temperature was below zero in an attempt to find a place to survive. The pronghorn used the highway because it was the only snow-free route.

“In the face of death and trying to survive, these animals can move great distances in a short amount of time,” Jakes said.

Applicable

The data collected in the study provides such great detail into how and when pronghorns use the landscape that it can be applied to pronghorn movements in other places.

“This is a neat advancement into understanding what’s going on beneath those movements and extrapolating out to other habitat,” said Nicholas De-Cesare, a research biologist with Montana Fish, Wildlife & Parks who worked on the statistical modeling.

On the ground for Malta-area FWP wildlife biologist Brett Dorak, the study provided information that led to the installation of flashing lights and warning signs on Highway 2 and Highway 191 where the animals cross the roadways. He’s also worked with ranchers on installing wildlife-friendly fencing and habitat restoration.

Seasons

Among the studied pronghorn, spring migration started around March 22 and continued until about April 10, lasting on average about 20 days. As they moved, the animals avoided large waterways and sought out vegetation that was the first to green up.

Fall migrations were shorter, running from around Oct. 31 to Nov. 10, lasting on average about 11 days. Unlike the spring, pronghorns followed waterways in the fall, sticking to higher, south-facing ridges above creeks and rivers that were more likely to be free of snow.

The fall movement south enables pronghorns to find large areas of sagebrush that provide greater nutrition in winter than grasses and forbs.

Based on what the study revealed, the scientists involved recommended protecting and managing native habitat; and easing movement across highways and busy roads that can inhibit their migrations.

They also hope to continue communication, data-sharing, and management between agencies and nations since wildlife do not recognize human borders.

“When we stand on a small piece of native prairie here in Alberta, Canada, looking toward our neighbors to the south, we lose perspective of the bigger picture and what is happening on the big stage,” Jones said.

“Those kinds of wildlife movements are uncommon across the world, and they are possible because of the widespread and deep-seeded appreciation for wildlife in northeastern Montana communities,” Gude said. “Private landowners, conservation organizations, and government agencies have worked for decades to make the landscape in northeastern Montana into one that can support such an incredible phenomenon, and they should be proud of it. They have done this on a landscape where people are also making a living, making it a remarkable conservation achievement in today’s world.”

French may be contacted at french@billingsgazette.com.