Wildlife Migration

Animals in any environment have many essentials for survival. Two are obvious and are needs that we have. The need for food and water. Many don’t consider other essentials that are very much like the needs humans have. Those include cover from the elements, cover from predators, protection for newborns. Humans can put all those together in one place, our homes.

Many animals need to move between numerous habitats to have access to all their needs. These movements are called migration. Climate change and extreme weather are affecting animal migration patterns, with many species moving north and to higher ground.

There are different kinds of migration. Daily animal migrations, also called diurnal or diel migration, involve the 24-hour cycle of the day. Animals move from one habitat to another and back on these daily cycles. This behavior is common in many animals in the mountain habitats around us. In many mountain valleys, elk and deer move out of the nightly protection of the trees and into the meadows to feed on the grasses and shrubs. They move back to the trees around sunrise.  In the winter, daytime is shorter. Sunrise and sunset happen while people are traveling to work in the morning and home at night. This is the same time the deer and elk are on the move, their daily migration. Many vehicle collisions with elk and other animals occur at this time. The Colorado Department of Transportation (CDOT) states that November sees more car accidents involving wildlife than any other month.  Drivers need to be especially alert around dusk and dawn. Often a driver encounters an animal on the roadway and swerves to avoid it and the result can be even more severe. People will often focus on the first animal to cross the road and collide with other animals in the group. Around 5,000 deer and 700 elk are killed each year by vehicle collisions in Colorado. Around 200 people die in the United States from crashes caused by wildlife and an average of 26,000 people are injured.

Migrating animals are often blocked by roadways that cut through their historic migration routes.

These collisions can be costly, averaging $3,103. It is estimated that in Colorado around 14,000 collisions, costing a total of over $40,000,000 in property damage occurs each year, and most go unreported. Coloradans who are involved in crashes involving wildlife pay about $66.3 million annually in medical expenses, according to CDOT and the Colorado Wildlife & Transportation Alliance.

Daily animal migrations are becoming more and more difficult for the wildlife because of the construction of structures, fencing, and other man-made obstructions. The solution to keep drivers safe is to keep the animals off the roadways. Wildlife fences are being put up along many major roadways. They are generally very effective, but it blocks the ability for deer and elk to make daily and yearly movements between the habitats they have used for eons.  These fences also block longer terrestrial migrations. Most of the migrations around us are short, usually from higher elevations to lower elevations. The shorter routes save energy for the winter as the animals move between seasonal ranges to avoid weather and snow cover that makes feeding difficult. The lower valleys have historically had a better food resource, but that is changing as that area is also where humans choose to live. That development blocks travel and eliminates the food the deer and elk have relied on.

When fences were erected, housing constructed, golf courses, farms, and ranches developed, the traditional migrations were restricted or completely blocked. The animals had to change their behavior. The large populations of elk died out. In previous decades, areas in Eagle County saw large herds of elk in the valley. In the last few decades those herds have disappeared. Twenty to thirty years ago elk were often seen on the west facing hillsides of Dowd Junction. They are no longer there. Many large herds of elk were in the meadows between Avon and Eagle. Many of those meadows no longer exist, and the valley has been interrupted by I-70. All of that caused the population of elk to decline.

Poorly designed fencing may block migration, but animals that attempt to get past them may get caught and that can lead to the death of those animals. This pronghorn did manage to escape.

The elk also changed their behavior. Moving into the forests is now a bigger problem for them and they are now frequently seen during the day bedded down on ball fields and parks in those areas. That leads to other issues for them as they are disturbed by people and people with dogs.

In 2019, Governor Polis signed an executive order to conserve Colorado’s Big Game Winter Range and Migration Corridors. The Colorado Parks and Wildlife Commission (CPW) also adopted a resolution reaffirming the Governor’s Executive Order and supporting federal funding opportunities.

“Safe Crossing for Colorado Wildlife and Motorists Act,” a bill signed by Colorado Governor Jared Polis in June of 2022, created the Colorado Wildlife Safe Passages Cash Fund. CDOT uses the fund for projects that provide safe road crossings and connectivity for wildlife. The objective is to increase motorist safety by reducing wildlife-vehicle collisions.  More than forty wildlife underpasses and three overpasses have been built by CDOT, with more planned using state and federal dollars. Long stretches of wildlife fencing are used to funnel the animals to the safe passageway. Those passages have made an enormous impact: Reductions in wildlife-involved crashes hover around 90% in Summit County and other locations.

Fencing along highways often has escape routes designed to let animal find a way off the roadway.	Underpasses, like this one in Summit County, are very effective and are favored by deer, bears and mountain lions.

These safe passages are used by the wildlife. Cameras and sensors record the traffic using them. Deer, bears and mountain lions seem to favor an underpass. Elk, bighorn sheep and pronghorn are much more likely to use an overpass. The smaller critters like mice, voles, weasels, snakes and frogs use the passages as well. Some of the passages have branches, sticks, and rocks where they can hide when using them.

CPW Wildlife Movement Coordinator Michelle Cowardin says the animals need to see through the structure and understand that their habitat continues on the other side. Tunnels that are too long will frighten many species, though in some cases, they seem to lend a hand to one another. Cowardin is often brought in as the wildlife movement coordinator. One of her responsibilities is helping design the wildlife crossing structures.  Humans have also eliminated many animals from the environment. This has changed ecosystems and that has impacted the plants and animals in them as well as the migration patterns the animals used. The elimination of one species or the introduction of non-native species may cause significant changes. This radical change is called a trophic cascade.

Research on the wolves in Yellowstone show that when the wolves were eliminated, elk moved into the valleys and browsed excessively on the willows in the valley floors. Willow stands must be more than 6 feet tall to make them beyond the reach of browsing elk and allow for new young willows. The loss of the willows caused a loss of the building materials used by beaver. The loss of beaver ponds changed the riparian environment and impacted the fish in the streams and the songbirds that use the area. Migrations of animals through these areas also changed.

When wolves were restored an ecologically complete ecosystem in Yellowstone was recreated. This reduced the impact of elk on the willows. More willows meant more beaver. Streams were slowed allowing even more willows. The fish and songbirds returned, and migration patterns were restored.

We often have a greater impact on wildlife and their migrations than we realize. Understanding our impact and working together to support Safe Passages and other initiatives can help to mitigate issues for wildlife.

This article is from the Eagle County Community Wildlife Roundtable. Text and Photographs by Rick Spitzer

The Eagle County Community Wildlife Roundtable is a collaborative partnership with the White River National Forest, Colorado Parks and Wildlife, Bureau of Land Management, local government entities, community members, and citizen scientists. The purpose of the Eagle County Community Wildlife Roundtable is to gather a group of diverse stakeholders in the valley to understand and address issues facing wildlife populations. Together we will identify a shared vision and realistic actions that the community can rally around to support wildlife. We want to leverage diverse values, creativity, and resources to move toward positive action.