Utahns know what extreme summer heat feels like. It’s not great. Now, imagine how it feels for a 1,000-pound moose covered in thick, dark fur.
“Large mammals are potentially particularly vulnerable to increasing temperatures just because of their large body size,” said Justine Becker, an assistant professor in the Department of Ecology at Montana State University. “It creates a lot of thermal inertia.”
The concern, she said, is that large mammals may not be able to adapt quickly enough for Earth’s current rate of warming. Summers are getting hotter in Utah and around the world, thanks to climate change driven by greenhouse gas emissions. July was the warmest ever in the contiguous U.S., breaking a mark set during the Dust Bowl of 1936.
“It would take thousands of years, probably, for their populations to adapt in an evolutionary sense to these increasing temperatures.”
What animals can do is move. Some seek cooler air at high altitudes. Others trade the open plains for shady forests.
This type of adaptation is called behavioral plasticity, and a study Becker co-authored examined this dynamic across the greatest number of large Rocky Mountain mammals ever looked at simultaneously. She and researchers at the University of Wyoming analyzed GPS data for nine different species, from bighorn sheep and mountain goats to wolves and cougars, in the greater Yellowstone region from 2001-2019.
The goal was to see how animals changed their behavior to cope with warming temperatures and what that tells us about their potential to adjust in the future.
“We're nowhere near the thermal maxima for any of our species,” Becker said. “But decades from now — if the temperatures are increasing in the way that it's predicted that they will — then these animals are going to get much closer to that point and really need to rely on environmental conditions to mitigate heat stress.”
Becker’s research team found every species showed some degree of behavioral change linked to rising temps. Animals in more homogenous environments, such as pronghorn in high desert grasslands, exhibited the greatest behavioral changes.
“This suggests that they are already dealing with some degree of thermal or heat-based challenges,” Becker said. “What that means is that if they don't mitigate these increasing temperatures and find ways to cool down, they are going to pay a physiological cost to that.”
That could lead to poor health, lower birth rates or even death, she said.
How freely an animal can move is often determined by how connected the landscape is. That’s where humans come in.
“Having those habitats there is important,” Becker said, “but it's just as important to make sure the animals can actually access those areas.”
Highways can be deadly barriers. Estimates say between 9,000 and 14,000 large animals are killed on Utah roadways each year, said Makeda Hanson, who coordinates the state-run Utah Wildlife Migration Initiative. That’s around 25 deaths per day.
Although those numbers may not be high enough to have population-level impacts, she said it’s still a major problem. Other causes of death disproportionately target weaker members of a herd, but crashes often take out animals in the prime of their lives.
“Wildlife collisions aren't selective,” Hanson said. “So it's impacting our does that are having babies more than, say, malnutrition or something else that's happening on the landscape.”
Having to change their behavior in response to heat can stress an animal, she said. If they have to sink hours into traveling long distances, that may limit how long they can feed or rest.
“They may spend more time shaded up than they would be foraging, which can influence how much fat they're able to accumulate,” Hanson said.
A warming planet can also invite more invasive plant species, such as cheatgrass, to take hold in the habitat, potentially hurting the animals’ food supply and increasing wildfire risk. Warmer winters can also boost tick populations, which can plague large mammals, and draw animals further into developed areas where there’s conflict with humans.
Still, there are things Utah can do to give large mammals a better chance. Hanson’s team uses GPS collars to document wildlife movement and then prioritizes habitat restoration projects based on that data.
Utah’s GPS collaring program has been going since 2014, she said, and has gathered location data on 47 species, including deer, bighorn sheep and moose. The state typically collars around 1,000 new animals each year, and the collars last for around four years. So, Utah is tracking between 3,000 and 4,000 big game at a given time.
“We use that information to determine where those really critical areas are that, if they were developed, could have really negative influences on the population,” Hanson said.
Utah has installed around 60 crossings specifically built as migration corridors, she said. Most have focused on mule deer migration sites, she said, because they tend to have more predictable movement patterns than elk, pronghorn or other species.
This work is unfolding now along US-89 in southern Utah, where the state is in the middle of a multiphase project to add wildlife crossings and fencing. The state launched a first-of-its-kind project on State Route 73 near Eagle Mountain that uses thermal technology to detect roadside deer and trigger a flashing light to alert drivers to animals.
Utahns can get involved as they drive around, too, by logging roadside carcasses with the Roadkill Reporter app. That information can help determine where Utah may need its next wildlife crossing or fencing project.
