By Jason Clay
Colorado Parks and Wildlife officials observed a compelling intersection of two wildlife projects at the end of July, when a deer affixed with a GPS satellite collar gave off a mortality signal just east of the Continental Divide.
At the same time, a mountain lion also being tracked by a GPS collar deployed in CPW’s lion density monitoring work on the West Slope, showed it was nearby the location of the mule deer’s mortality signal.
A wildlife officer hiked into the location, found the carcass of the doe and placed a trail camera at the site. That camera picked up the collared mountain lion consuming the collared deer.
To wildlife officials, it showed the uniqueness of these two marked animals crossing paths as nature would have it. The circumstance also presented an opportunity to share what can be learned from collared deer and mountain lion projects.
“Better understanding species interactions, in particular predator and prey, is a huge benefit that has resulted from GPS technology,” said CPW Terrestrial Biologist Bryan Lamont. “In this case, both of these animals had traveled many miles away from where they had originally been caught and collared to only randomly cross paths. When determining female mule deer survival rates, this kind of information can help managers more accurately calculate the exact causes of mortality.”
CPW has been monitoring mule deer populations, particularly population dynamics and the relationship to winter survival, on the western slope for over two decades.
Wildlife officials monitor herds in five intensive mule deer geographic areas with the use of GPS satellite collars that allow managers to track the animals. Weekly snow measurements combined with temperature data also help biologists understand how winter conditions may influence mule deer survival.
The ability to survive is limited by the quality and quantity of forage and predation. That can be compounded by the severity of the winter and also population density, as competition over the available forage can increase their probability of succumbing to mortality factors such as disease and starvation or malnutrition.
The two most limiting factors for the growth of a mule deer population is the survival of does and fawns.
The doe mule deer killed and consumed by the mountain lion in this specific case was collared in 2020 between Kremmling and Ute Pass. The mountain lion’s collar was deployed in January, 2021 in northern Middle Park.
Mountain lions prey primarily on ungulates, especially deer, but also elk, moose, bighorn sheep and pronghorn. Prior research studies by CPW of mountain lions on the Front Range showed that 66 percent of lion kills were of mule deer, with over half of those being fawns. On average, a mountain lion could consume a deer a week.
“While it is very uncommon, from time-to-time we will have a collared mountain lion interact with a collared deer, particularly collared fawns,” Lamont said.
The reason this mountain lion had a GPS satellite collar is because the animal is a part of a new project CPW launched last winter to better understand lion population numbers on the west slope. A 10-year project looking at multiple study areas, it started in Middle Park for the first 2-3 years. You can learn more about the lion study from this video produced last March.
After collaring 25 lions last winter, biologists are now relying on trail cameras to help them derive lion density in the study area.
“We can use that sort of relationship of marked individuals and unmarked individuals over a month or two of sampling in the winter to actually get a density or abundance – a number of mountain lions in that population – as an estimate,” said Mark Vieira, CPW’s Carnivore and Furbearer Program Manager.
Although the trail camera that captured the convergence of the deer and mountain lion was not part of either study, it did capture a little bit of Colorado’s wildness. Mountain lions are rarely seen feeding on their prey.
“Mountain lions are amazing creatures in terms of what they are able to do, taking down animals that are three or four times their size, and at the same time staying largely undetected by people,” Vieira said.
The population size of the deer herd the collared doe comes from (Data Analysis Unit D-9) was estimated to be 13,470 animals in 2020. Colorado has an overall statewide population of greater than 427,000 deer. CPW estimates we have 3,800 to 4,400 independent/mature mountain lions, not including dependent young, in Colorado.
GPS coordinates from collared wildlife are sent to biologists through email, texts and collar database software.
“Technology plays an important role in wildlife management for the collection of necessary data to inform decisions,” said Shannon Schaller, Deputy Regional Manager for CPW’s Northeast region. “This intersection of projects was illustrated with those technologies.”