Colorado has one of the fastest-growing populations of any state in the country. In 2019, for example, the state expected to grow by 1.32 percent, putting it firmly in the top ten in terms of growth. Many of the newcomers are attracted to the state because of its outdoor recreation possibilities. Indeed, it’s not just Colorado drawing new residents for outdoor fun; seven out of the ten fastest-growing states are the mountainous western states.

Increased space taken up by housing and infrastructure for people naturally affects the wildlife that lives in states like Colorado, but it isn’t just construction and traffic that disturbs animals. As those people fan out onto trails, ski lifts, into the rivers, and the summits, wildlife takes note. The behavior of animals changes. And recent studies are showing that their populations can plummet.

This especially seems to be the case with elk in Colorado. Biologists make aerial surveys of elk populations, counting the majestic animals from above to estimate herd sizes and to take stock of reproductive success. In the area surrounding the posh resort town of Vail, biologists in years past regularly counted 1,000 head of elk in a population called “Unit 45.” But last February aerial surveys counted only 53 animals.


As elk numbers in the area plummeted, the number of backcountry wilderness and trail users skyrocketed. Since 2009, Vail area trail use has reportedly doubled, according to The Guardian and the Society of Environmental Journalists. Hiking, trail running, and mountain biking are the quieter uses of backcountry spaces, but off-road vehicle use has also increased. It’s not just during daylight hours, either. Use of trails in the area at night has increased by 30 percent.

Wildlife managers think this explosion of trail use, not construction, or roads, or vehicular traffic by itself, is what has caused such a dramatic and rapid decline of the elk population.

Studies from Colorado State University have shown that as people enter a backcountry area, elk tend to leave. Or, if nothing else, they’re disturbed enough to get up and move around. When this happens to cows with calves, the effects can be deadly. Bothering elk cows has a direct result on the mortality rates of calves. This is a problem for pregnant cows, as well as cows that are already nursing calves. If pregnant cows were disturbed too often, according to the CSU study, the calves would die. If the nursing mothers were bothered often, their calves died too. Research doesn’t explain why, necessarily, it’s thought that nursing calves don’t have the strength to follow their mothers if they flee from people and become easy prey for predators tracking the herd.


Tule elk in Point Reyes National Seashore. Photo: Kyle Glenn.

A similar study conducted in 2012 in Point Reyes National Seashore, just north of San Francisco, California, showed something similar when a resident Tule elk herd was studied in the presence of hikers. Hiking disturbed the elk, as you might expect, but so did the presence of people in kayaks along the shores of Tomales Bay, near where the elk roam. This was especially apparent during the rutting season.

Researchers participating in the Point Reyes study wrote that they wondered how the constant disruption of the elk herd by hikers would affect the reproductive health of cows as well as their calves, but it was outside the scope of that particular study.

It’s also known that the mere sounds of the human voice can freak out predators so much, entire food webs can be disrupted.

Back in the Vail area, wildlife managers have taken to closing certain trails that may impact calving areas and to organize campaigns that educate people as to the importance of staying out of closed areas that are there to protect the elks. When biologists flew over the elk grounds to count their numbers, they noted fewer elk tracks than they expected to see and a whole lot of backcountry ski tracks.

It’s hoped that education and trail closures can reduce pressure on the elk and help increase population numbers.

Top photo: David Rupert