The iconic species is in decline. New data is helping game managers address the problem
On the road again: A group of mule deer bucks moves across Oregon’s Malheur National Wildlife Refuge. The state is watching. Photo: Barbara Wheeler/USFWS
By Kendra Chamberlain. April 16, 2025. As mule deer populations continue to decline across the West, the Oregon Department of Fish and Wildlife (ODFW) says it will use better data to manage its annual mule deer hunts.
Specifically, the department wants to update the state’s mule deer hunting units to track population changes.
“Mule deer are struggling across the western United States,” ODFW’s spokesperson Michelle Dennehy told Columbia Insight. “So this is very urgent, because we want to see the species continue to thrive, but they’re in troubled times. And that’s not just the case in Oregon—it’s the case all over the West.”
Hunters and conservationists alike have bemoaned the decline of the big-eared ungulate. But researchers are having a hard time understanding why exactly mule deer populations are suffering.
In Oregon, a 2022 count pegged the population at 162,600 animals, just over half of the 300,000 estimated in the 1980s.
Mule deer populations have always been variable year to year. But since the early 2000s, the state has seen a steady decline in the species, mirroring a larger trend throughout the West.
Habitat degradation
ODFW, like other state wildlife departments in the region, has spent the past decade conducting research to better understand why mule deer populations are struggling.
The department began deploying GPS radio collars on mule deer in 2014 to get a better sense of how herds move across the state. That research has led to stronger population models to monitor the species, incorporating data on herd composition, movements and survival rates.
In Oregon, at least, habitat degradation and loss appear to be the driving factors in mule deer declines. The species is struggling to find enough nutrition to support larger populations.
“Some of it’s related to changes in forest management. And we have invasive species like Medusa head rye that come up after fire—that’s reduced nutrition,” said Dennehy. “We’ve also seen that the growing season is shorter than it used to be, and that’s reduced their nutrition.”
Last year, the department adopted a new mule deer management plan to address population declines. The plan noted that it’s not just that the amount of habitat has decreased, but that the carrying capacity of the landscape (how many mule deer the remaining habitat can support) has decreased, too.
Oregon’s mule deer are likely suffering from “chronic nutritional stress in response to long term declines in carrying capacity,” the plan states.
Development also plays a role. Roads and fences can impact mule deer access to food and interfere with migration routes, the knowledge of which mule deer pass on from mother to offspring, generation after generation.
Renewable energy development is another rising threat to mule deer in eastern Oregon, as reported by Columbia Insight.
Updating obsolete boundaries
Oregon uses wildlife management units (WMUs) developed in the 1950s to control mule deer and other big game hunting. These units were designed to spread hunter distribution, but they don’t actually reflect how mule deer move across the state throughout the year.
ODFW has proposed updating unit boundaries to better reflect herd movements, rather than rely on the artificial boundaries enshrined in current WMUs.
Among other things, the change would allow the department to track population responses to actions aimed at helping the species recover.
“If we do something [such as] habitat improvement, we want to be able to measure the response accurately. And if we’re misaligned on our data, that makes it harder to detect the response,” said Dennehy.
Mule deer migration routes map: ODFW
The new hunting units will need to be approved by the Oregon Fish and Wildlife Commission later this year, and if approved won’t go into effect until the 2026 hunting season.
If approved, the change would present a major shift in mule deer hunting units in Oregon, said Dennehy. The units will be larger than the current WMUs and likely have different names.
“Changing it for hunters is a big deal because they’re accustomed to this hunt structure. There are hunters out there who’ve been putting in for years for a particular hunt and that’s part of the reason we’re getting out a year in advance,” she said. “We know how important this is to hunters.”
Not to mention mule deer.
