JWM: Hunting didn’t alter Wyoming mule deer migration timing

Hunting season in south-central Wyoming doesn’t seem to impact the timing of migration for mule deer, but it does seem to prompt bucks to seek areas away from roads used by hunters.

Males and females have different migration patterns, researchers found, driven more by weather and conditions on the ground than by hunting.

“One of the big questions we looked at was to see if this huge pulse of human activity that occurs on the landscape during hunting season alters the timing of when deer leave their summer ranges and head to their winter ranges,” said Patrick Rodgers, an associate research scientist at the Wyoming Migration Initiative at the University of Wyoming and lead author of a recent study published in the Journal of Wildlife Management. “Timing of migration is so important for deer to garner the effects of migration by avoiding deep snow and tracking the best food on the landscape.”

The idea for the study came about when a Wyoming Game and Fish Department biologist was drop-netting female deer to capture and collar them in their summer range in south-central Wyoming, Rodgers said. While doing so, he also ear-tagged some bucks. As time went on and it got closer to migration time, he sighted some of the bucks he had tagged pretty far from the does. “It was this aha moment of, maybe bucks have different migratory behaviors than females,” Rodgers said. On top of that, Rodgers and the team of biologists wondered if hunting was a factor in migratory behavior, especially since most hunters go after bucks rather than does.

Researchers used GPS tracking collars and radio telemetry to determine where mule deer were traveling on their migration. Credit: Patrick Rodgers

He and his colleagues decided to test this hypothesis and determine if any other factors influenced mule deer (Odocoileus hemionus) migrations such as weather, food quality or the distance deer migrated.

The team drop-netted and helicopter net-gunned 95 mature bucks and fit them with GPS collars. “Drop netting is like a big party tent for deer,” Rodgers said. “We put apple pulp, a tasty treat for them, and they all show up and we drop the net on them.”

In addition, other researchers had already been collaring female mule deer for a different study, so they used that ongoing data to compare buck and doe movements. They tracked the animals for three years. Capturing and collaring enough animals was important, Rodgers said, since many of the deer had been hunted or died of natural causes throughout the study.

After running analyses, the team found that hunting was not the main factor influencing the timing of migration. Males, they found, were more likely to leave their summer range earlier to get a head start if they migrated longer distances to winter ranges. Snowfall was likely to trigger when both males and females left the high country.

“Moving through deep snow is taxing for mule deer,” Rodgers said. “The sooner they are able to avoid heavy snow accumulation in the high country, the better for them.”

This showed the team that hunting is sustainable in this area of Wyoming. “Wyoming Game and Fish Department has a pretty good grasp on how hunting affects movements,” Rodgers said.

He and his colleagues also found that during autumn rifle season, bucks moved farther from motorized routes. “In our study area, there’s a heavy hunting pulse in the fall, with a 12-day hunting season,” he said. “And most of that hunting was done from vehicles and ATVs.” Their research showed that when hunting season rolled around, bucks were able to find areas away from the disturbances to help buffer them from the nearby roadways with human activity.

They didn’t observe that pattern in does, though. Does tended to use areas that retained the highest quality forage. “It was more important for females to focus on putting on those last few calories before winter hit because winter could be especially taxing for deer,” he said.

Roadless areas on summer ranges in the area likely served as an adequate buffer from hunting disturbances, Rodgers said. In areas where hunting may affect migration timing, he said, managers may want to “create more roadless areas to help buffer some of those negative effects.”

This article features research that was published in a TWS peer-reviewed journal. Individual online access to all TWS journal articles is a benefit of membership. Join TWS now to read the latest in wildlife research.