From hunt camp to the hardware store, rumors swirl about the cause of declining mule deer numbers. What’s the truth, and how much are elk to blame?

I grew up in a family of bass fishermen from the Florida panhandle. By the time I made it to Wyoming as an adult, the “good old days” of mule deer hunting were long gone. In the years that I’ve been out West, I have heard myriad reasons why this is the case – everything from “too much development” to “too many side-by-sides” – but I took some time this fall to get to the bottom of it.

As it turned out, the answer to why we’re seeing fewer mule deer proved more complex than I thought. There were times when science seemed to be overruled by anecdotal evidence from those who’ve spent more time in the field than some biologists. Other times, scientific studies provided a clear lens through which I could view these problems. The more questions I asked, the more apparent it became that at the root of it all lies the mule deer’s sensitivity to change.

To understand the mule deer’s decline, one must first understand the mule deer itself. Mule deer, perhaps as much or more than any other ungulate (hoofed mammal) found in the lower 48, rely heavily on memory-based movements to avoid predation, find food and acquire mates. A mule deer will migrate to the same winter range – using the same path, no less – year after year. This migration route is embedded in their mind and they’ll seldom stray from it. This is different from the oriented movements (sight, smell, sound) grazing cattle rely on, for example. They’ll often use their eyes to spot quality feeding grounds.

Biologists say mule deer can only tolerate a less than three percent change to their environment before they start to be negatively impacted. These changes – often referred to as “disturbances” in academic literature – cause a litany of negative effects, including loss of forage, decreased lactation resulting in weakened fawns that have trouble surviving the winter, and an inability to escape predation.

Animals with a high memory capacity, like mule deer, are believed to have low behavioral flexibility (they don’t change their behavior as the environment changes). Think of it like this: can you remember those toy trains you’ve seen around the holidays? The locomotive is the mule deer, and their migration pathway is the track. Imagine if you were to remove a piece of the track – what happens? The train derails and crashes. When a new disturbance pops up in the migration corridor, a piece of the track is essentially removed, often resulting in devastating effects.

The most common answer to the reason why mule deer experience disturbance is manmade habitat loss. Wind farms, roads, mountain resorts and subdivisions aren’t good for mule deer, but we hear about those more because they fit squarely into our country’s current political discourse. Hell, there’s a hit show on TV right now about land development in Montana (and boy, do I like watching Rip kill people), but development doesn’t fully explain the challenges mule deer face.

When a new disturbance rears its head in the mule deer’s environment – like a new mountain resort – it’s easy to define that disturbance in terms of size. The development might encompass only 20 acres, and the ranch it’s built on might be over 1000 acres. You’d say, then, that there’s still plenty of habitat for the mule deer to use – but you’d be wrong. That 20 acres is direct habitat loss, but it doesn’t account for indirect habitat loss as a result of avoidance behavior.

Avoidance behavior simply means the mule deer are going to avoid places in and around disturbances. If there’s a lot of traffic and pressure on that ranch, the deer might avoid much of those 1,000 acres altogether, regardless of how good the forage is around the development. Indirect habitat loss opens up a brand new can of worms, including uncomfortable discussions about the state’s growing elk population.

“Elk are sexy. Elk are the popular thing right now,” one Wyoming native explained to me. “So, nobody’s going to want to blame the elk, because they’re a revenue driver and they get people to come to our state. I’d be surprised if there’s ever a study [that’ll be state-funded] that definitively links increased elk numbers to declining deer numbers.”

While it may be true we’ll never hear a public statement declaring elk the enemy, there are studies that show the effects of competition of resources. Elk are far larger than mule deer and it doesn’t take a scientist to know they’re going to win that competition. I spoke with a university biologist (who I’ve chosen to keep anonymous due to the nature of this website), who admits it’s possible elk are having a negative impact on mule deer habitat.

“When these animals display resource partitioning, where species disperse in such a way that divides up resources between them in order to avoid competition, it can also have an indirect effect on available habitat,” she explained. “You can imagine a mule deer population occupies a region, then suddenly elk expand into that region, so they have to split those resources not only between other mule deer but also with elk now. The trouble is that it is difficult to study competition and to absolutely know whether what you’re seeing is actually competition or not.”

Competition may be difficult to study, but it’s easy to see with your own eyes. Last year, during my seven-day high country hunting trip, elk appeared to outnumber mule deer 20-to-one. Prairie areas that once saw an abundance of deer now hold a sizeable elk herd – the mule deer are few and far between.

“I used to come out here and see 10 or 12 good bucks per day,” a friend told me last fall. “Now, you’re lucky to see one worth shooting. I can come out here and find a herd of bull elk in about half an hour, though, which was never the case. You tell me.”

If an argument can be made that elk are impacting mule deer numbers, the same argument can be made for the growing whitetail population. Mule deer won’t usually occupy the same areas as whitetail, so there’s naturally going to be a loss of habitat there as well.

Another uncomfortable point of discussion is the manner in which some hunters chose to behave while looking for mule deer. On the prairie, it’s not uncommon to see droves of ATVs and side-by-sides roaming the maze of “two-track” roads. I asked my biologist how these vehicles might impact mule deer numbers.

“Knowing how mule deer respond to any sort of disturbance, yes, I would guess that that would cause mule deer to alter their behavior in some way,” she said. “They’re likely avoiding areas of high ORV presence, which would result in indirect habitat loss via avoidance behavior.”

These off-road toys are becoming increasingly popular in the Mountain West, and it’s becoming more difficult to find areas where a hunter can avoid them. Some folks view hunting season as another reason to break out the side-by-side, rather than heading out for the hunt itself.

“It’s part laziness and part ignorance,” my friend said. “They’re too lazy to get out and hike around and actually look for deer, and they’re too stupid to know they’re driving the deer out. I wish they’d do something about it, and I hate being this cynical, but I’m pretty sure [local governments] don’t want to lose revenue from ORV tag sales.”

So, what’s causing declining mule deer numbers? Well, just about any disturbance to their habitat. To reverse this sad trend, it’ll take a concerted effort from all fronts. New developments in migration corridors, like the luxury resort that was just approved near Bondurant, need to stop. Tag allocations need to be reassessed (perhaps more elk tags and fewer deer tags). Hunters and recreators need to be aware of their impact while using off-road vehicles. Local and state politicians need to step up. Wild places need to stay wild.

It all starts with education and an understanding of the mule deer’s behavior. If meaningful actions aren’t taken soon, it won’t just be the “good old days” that’ll be gone – it will be the mule deer itself.