To understand how climate change might impact mountain lions and other key wildlife species in the American Southwest, David Stoner looked to the sky.
Specifically, he used NASA images to study the landscape and look for clues on the animals’ distribution. Stoner is a biologist in the Department of Wildland Resources at Utah State University and one of the state’s top mountain lion experts.
Cougars are a contentious issue in Utah. They’re valued as trophy animal by houndsmen and hunters. They’ve become a beloved icon of the West for conservationists, especially as the cats disappear in other parts of the country.
They’re also notoriously hard to track, but their main prey species, mule deer, are not. And the food that deer eat is much easier to map from above using NASA satellites.
“When I talked to people about this, some were confused, they thought we were actually counting the animals from the imagery itself,” Stoner said. “That’s not the case here.”
Even with high-resolution images, counting cougars would be tedious if not impossible, given their tawny camouflage. That’s why Stoner looked at vegetation instead.
Plants tend to absorb visible light with the chlorophyll they use for photosynthesis, but they reflect near-infrared sunlight back into space. That makes plant cover and density possible to calculate with satellites.
“Think of it as an index of greenness,” Stoner said.
Since mule deer are herbivores, it follows that where there are more green plants, there are more deer. And where the deer go, cougars follow.
Mountain lions generally eat just under one ungulate a week, preying on an average of 38 deer each year according to a study from 2010.
Stoner wasn’t just curious about the prey and predator populations’ distributions. He wanted to understand how climate change could impact their range in the future.
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He teamed up other scientists from Utah, Arizona and Nevada, as well as some geoscientists from Maryland, to analyze the Great Basin, the Colorado Plateau and the Mojave Desert — a region that’s expected to become hotter and drier in the coming decades.
The map they made shows denser of cougars populations across the Wasatch Mountains and the Rocky Mountains of the Colorado Plateau.
“As you would expect, the mountains are wetter. They have more vegetation, therefore they support more animals,” Stoner said. “In the West, the higher you go the wetter it is.”
In those mountains and foothills, Stoner calculates there’s four to five mountain lions and 1,300 to 1,900 deer per 100 square miles.
By contrast, desert habitats that support the animals have sparser populations. Per 100 square miles in those areas, there’s two mountain lions and around 750 deer at best.
By comparison, Nevada’s Great Basin Desert has fewer deer and cougars per 100 square miles — at best, there’s around two cougars and 750 deer.
Stoner also knows from past research that cougars tend to roam bigger territories where it’s drier and less vegetated. He radio collared mountain lions in sheep range north of Las Vegas and tracked their movements.
“It’s very dry, very arid,” he said. “There are very low prey densities. Those animals had huge ranges.”
He also collared some cougars in the Oquirrh Mountains in the western Salt Lake Valley.
“Which, by comparison, is very productive. It’s very wet and has very high prey densities,” Stoner said. “So animals in Oquirrhs have a small range by comparison.”
The satellite study helps biologists like Stoner understand the way climate can work its way through the food chain.
It also shows how climate change could lead to more conflicts with wildlife, particularly as human populations continue to grow in the West and development further fragments cougar and deer habitat.
“If the Southwest becomes warmer and drier ... in general, cougars will increase the area they need to meet nutritional requirements,” Stoner said. “In wetter climates, this might not be a problem. In the arid West, it is.”
Urban areas in the West could become more attractive to the animals, because irrigation creates more reliable vegetation.
“So if the neighboring wildlands are dry but urban and agricultural areas are productive, that’s going to be an attractant for animals, both deer and cougars,” Stoner said. “We see this already.”
Stoner published his findings in the journal Global Change Biology this week. He said the research could prove useful to management agencies like the Utah Division of Wildlife Resources.
“It’s predicting animal densities all over the state, not just in one (hunting) unit or another,” Stoner said.
The Utah Wildlife Board will determine whether to raise the cougar hunting quotas on Aug. 30, a decision they make based on cougar population estimates calculated by DWR biologists.
Those estimates have come under fire by both hunters and wildlife conservationists for being inaccurate and failing to consider the importance of cats’ social structures.
DWR estimate there are around 2,000 adult cougars and 2,000 kittens or yearlings.
Darren DeBloois, DWR game mammals coordinator, said the division is open to studies that better establish mountain lion numbers and migrations in the state.
“That’s probably the best way to do it, even on an eco-region basis,” DeBloois said of the satellite research. “You want a big picture because (mountain lions) can move so far.”
Still, DeBloois took issue with some of the study’s estimates.
“The only weakness I see in that is the greenness,” DeBloois said. “I’ve got some concerns, because in some areas of the state it’s green but not necessarily good (deer) habitat, like juniper forests in the Uintah Basin.”
DWR is planning on doing its own study this winter, radio collaring females and kittens to better understand their survival rates.
“We’re all coming at it from different angles, at the end we hopefully have a good way to figure it out,” DeBloois said.