Scientists working in and around Yellowstone National Park are tranquilizing mountain lions, fitting them with GPS collars, and tracking their movements to investigate a question wildlife managers and researchers are still trying to pin down: whether these solitary predators may influence how chronic wasting disease (CWD) persists and spreads in deer. The effort, which began in 2019 under the Wyoming Game and Fish Department, has since expanded into a broader investigation of how wolves and cougars compete over prey, and what that rivalry means for disease transmission across one of North America’s most watched ecosystems.
Collaring Cougars to Track a Deadly Deer Disease
Chronic wasting disease, a fatal neurological illness caused by misfolded proteins called prions, has been spreading through mule deer herds in Wyoming and neighboring states for decades. Yet the role predators play in that spread remains poorly understood. When a mountain lion kills and partially consumes an infected deer, the leftover carcass, or “cache,” sits on the ground for days, potentially concentrating prions in the soil. The Wyoming biologists who first focused on these cache sites in 2019 now use GPS collars to locate kills and evaluate how mountain lion predation intersects with chronic wasting disease in mule deer.
The collars transmit location data at regular intervals, allowing researchers to identify clusters where a lion has lingered, a reliable indicator of a kill or feeding event. Field crews then visit those sites to examine prey remains, catalog what species was taken, and, where relevant, collect information and samples used to assess CWD risk. This ground-truthing process is essential because GPS coordinates alone cannot distinguish a kill from a resting spot. As the National Park Service has documented in its work on telemetry tools, clusters in GPS data can help researchers locate areas where an animal lingered and guide follow-up field checks.
How SMART Collars Decode Predator Behavior
The GPS units strapped to Yellowstone-area mountain lions are far more sophisticated than simple location trackers. Researchers at UC Santa Cruz developed what they call SMART collars, which pair GPS with built-in accelerometers that record the animal’s movement in three dimensions. To calibrate those sensors, the team worked with captive lions on treadmills while measuring oxygen consumption, then matched specific accelerometer signatures to behaviors like walking, running, pouncing, and feeding. The result is a library of movement fingerprints that lets scientists remotely reconstruct what a wild lion is doing at any given moment, and how much energy it burns doing it.
That energy data matters because it reveals how hard a cougar must work to survive. If wolves are forcing cougars to abandon large elk kills and instead hunt smaller, more agile mule deer, the energetic cost of each meal changes. SMART collars can detect that shift in real time by linking bursts of high-intensity movement to particular hunting strategies. Still, capture-based collaring is expensive and logistically demanding. A graduate study from Utah State University comparing capture–collar methods with noninvasive alternatives like camera trapping, snow tracking, and scat-detection dogs found that each approach carries distinct cost and detection limits. In the vast terrain of the Southern Greater Yellowstone Ecosystem, collaring remains the most reliable way to monitor individual behavior, even as researchers acknowledge the stress that sedation and handling place on the animals.
Wolves, Stolen Kills, and a Dietary Shift
The reason mountain lion diets matter so much for disease ecology traces back to a nine-year study in the Southern Greater Yellowstone Ecosystem that used contemporaneous GPS telemetry data from wolves and cougars. By investigating nearly 4,000 potential kill sites, researchers showed that wolf–cougar encounters are driven primarily by wolves locating and stealing cougar kills, a behavior ecologists call kleptoparasitism. Wolves do not typically seek out cougars to fight them; instead, they follow scent trails to fresh carcasses and displace the smaller predator. A recent analysis in a carnivore ecology journal extended this work, describing how multi‑predator interactions in this region shape the way cougars use a landscape shared with wolves and multiple prey species.
Long-term monitoring by Yellowstone staff shows that wolf packs are now a permanent part of this carnivore guild, with annual wolf reports documenting pack sizes, territories, and kill rates on elk and other ungulates. In that context, cougars appear to be adapting their hunting strategies to reduce conflict with a dominant competitor. When they shift their diets toward more deer and away from elk, encounter rates with wolves drop, but that adaptation carries a potential cost that current monitoring may not fully capture. If cougars increasingly target deer rather than elk, they are killing more animals from the species most vulnerable to CWD. Each cached deer carcass left in the backcountry could contribute infectious material to the environment; prions are known to persist in soils, which is one reason researchers are paying close attention to where kills and caches occur. The very behavioral flexibility that helps cougars coexist with wolves may be creating hidden reservoirs of disease across the Yellowstone region.
A Growing Predator Population Complicates the Picture
Mountain lion numbers across western North America have likely been climbing for years, a trend that adds urgency to the CWD question. Research in the Journal of Wildlife Management concluded that cougars have responded numerically to the recovery or removal of other dominant carnivores in different parts of their range, with local populations rebounding when persecution eased and prey became more abundant. In the Greater Yellowstone region, that means more cougars on the landscape at the same time that chronic wasting disease is advancing through mule deer herds, increasing the number of potential predator–prey encounters where prions could be redistributed.
Managing that convergence of rising predator numbers and an entrenched wildlife disease is complex. State agencies rely on hunter harvest data, conflict reports, and collar studies to decide where to allow more or fewer lions, and how to balance conservation with livestock and human-safety concerns. In Wyoming, many of those decisions are informed through internal data systems and public-facing tools accessed via the Game and Fish Department’s online information portal, which aggregates harvest records, license sales, and field observations. As chronic wasting disease spreads and wolf–cougar dynamics continue to evolve, those datasets, combined with the fine‑scale insights from GPS collars, will be central to understanding whether mountain lions are merely scavengers in a diseased landscape or quiet engineers of how, and where, CWD persists.
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*This article was researched with the help of AI, with human editors creating the final content.
