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From migration to diet, climate change makes things more complicated for Wyoming's big game

Pronghorn in Snow
Tom Koerner
/
USFWS via (CC BY 2.0) (on Flickr)
Heavy snowstorms can have devastating effects on pronghorn, especially if they happen out of season.

Hunting is a big industry in Wyoming, bringing in about a billion dollars in revenue every year. But as wildlife starts to feel the impacts of climate change, those effects could trickle down to hunters.

Doug Brimeyer is the Deputy Chief of Wildlife with the Wyoming Game and Fish Department. He said Wyoming's wildlife is already adapted to the state's unpredictable and harsh weather, but they can still be caught off guard, like the big spring snowstorm that happened last March.

"Wyoming is no stranger to extreme weather events. And last spring certainly was one of those that we saw some elevated mortalities and localized areas in southeast Wyoming," he said.

That storm led to a lot of pronghorn dying, primarily because they couldn't get through the snow to their food. Events like that can have big impacts on population numbers, which according to Brimeyer can be felt by hunters.

"We adapt, once we see that on the landscape when we document some conditions like that, we'll modify our season approach for numbers of licenses," he said.

But climate change is making extreme weather events less predictable, including how extreme they'll be and when they'll strike - which can mess with scheduled hunting seasons. Brimeyer said hunting tags are part of the department's overall management strategy for wildlife. They calculate mortality from hunters into their population objectives, which are reevaluated every five years. When a late storm happens now, Brimeyer said the hunting is often more difficult, but they don't change tag numbers until the next year when they do a new population estimate.

"It's kind of built-in that there's some variability, but after seasons are set, typically we let nature take its course and it's kind of a little bit self-limiting in terms of if people will have a high level of success if conditions are favorable," he said. "Sometimes we'll have fall conditions that are conducive to good hunting conditions and other times it may not be as much."

Brimeyer said so far they haven't seen any significant changes in big game over the long term, but some individual populations are faring better than others.

But extreme weather events like snowstorms aren't the only side effect of climate change. Droughts are growing longer and more intense in the region, which can make it harder for plants to grow.

"There's a mounting evidence that the habitat is changing, the behavior of these animals is changing and it's a matter of time to where we probably will connect that to understanding how the populations are affected by these changing conditions."

There's a common term used in migratory big game research called "surfing the green wave." It refers to the way that plants tend to green up in the spring, starting in lower elevations and then slowly moving up into the mountains. Big game animals like deer, elk, and pronghorn will follow that green wave up in elevation. Jerod Merkle, an assistant professor at the University of Wyoming in the zoology and physiology department and Knobloch Professor in Migration Ecology and Conservation, said this has to do with nutrition.

"The reason that big game are interested in that early spring forage is that as plants grow, they become more fibrous in order to grow taller and that fiber is not what big game are interested in," he said. "Like, us, we like to eat fiber. But the big game don't want to deal with that, they want nutrition in that forage and so they're looking for plants at early spring states."

But more intense droughts are making that green wave smaller and faster.

"When it's dry and warm in the spring, that green up moves very quickly, and kind of just removes the amount of time that the animals have to enjoy that really great forage in the spring," Merkle said. "When it's a cool wet spring, the snow is melting slowly, there's little patches of open areas where the green vegetation is coming out. And then that cooler weather makes the plant slowly grow and provides more time for the animals to access that good quality vegetation."

According to Merkle, some species are better at keeping up with this shortened green wave than others, like mule deer. But that doesn't change the fact that there's less nutritious food available, which means fewer animals can survive or reproduce. He said more research needs to be done, but right now it looks like regular shorter green waves could have a noticeable impact on population numbers.

Another nutritional hurdle that big game may have to face is the invasion of less nutritious or unpalatable nonnative grasses, like cheatgrass and medusahead. Climate change may make it easier for these invasive species to establish in the state.

"And we're putting some money into that to basically first assess where some of these species are at and then we're exploring with our federal partners and through WWNRT (Wyoming Wildlife Natural Resource Trust) to secure funds to address some management areas where we can treat some of those grasses that outcompete some of the native vegetation that are preferred for Wyoming's species," said Brimeyer. "We're hoping to stay on top of that, and we're putting quite a bit of investment in the invasive grasses at this point."

But there's a lot to learn still.

"There's a mounting evidence that the habitat is changing, the behavior of these animals is changing and it's a matter of time to where we probably will connect that to understanding how the populations are affected by these changing conditions," Merkle said.

One thing both Brimeyer and Merkle agree on is that climate change is a long-term problem and while there is some research, they still don't have a firm grasp on what it means for many species, including big game, and hunters.

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