Wildlife Roundtable: How climate change and development are impacting the migration of animals | VailDaily.com
YOUR AD HERE »

Wildlife Roundtable: How climate change and development are impacting the migration of animals

Rick Spitzer
Wildlife Roundtable
Bighorn sheep, like these in the East Vail herd, use south-facing slopes during winter because they are often snow free.
Rick Spitzer/For the Vail Daily

When people think of migration, they often think of the animals in the world that travel huge distances. Some of these migrations are amazing. They involve thousands or millions of animals and are incredible feats of endurance. Migration often involves traveling from one type of habitat to another. Animals migrate to find food, breeding grounds, or more livable conditions.

The most well-known migration is called The Great Migration. It is the movement of more than 2 million wildebeest, along with large numbers of zebra, and smaller numbers of various gazelles and impala. This is a predictable movement that covers around 620 miles. The migration crosses Tanzania’s Serengeti and Kenya’s Massai Mara. The animals follow the rain and are in search of grasses needed for survival. The large numbers of animals are why it is called The Great Migration.

But the distance is a short trip compared to what some animals do.



The Arctic tern has the record for distance. This small, gray-and-white bird travels from the Arctic breeding grounds in the North American summer to Antarctica for the Antarctic summer, a distance of 25,000 miles.

For land animals in North America, the caribou travels annually between tundra and forests in Alaska and Canada. The annual cycle covers as much as 3,000 miles. The migrations of the Porcupine caribou herds are among the longest of any land mammal.



Hotter, dryer summers are increasing pine beetle numbers and extending the season allowing them to cause greater damage.
Rick Spitzer/For the Vail Daily

There are many animals that migrate and some of them are here in Colorado. These species may not cover the great distances found elsewhere, but they migrate for the same reasons as other species.

Colorado’s big game animals migrate along routes used for centuries to find better forage, a place to birth their young or to find better environmental conditions. Some move from lower winter elevations to higher summer elevations. They may also move simply to find forage that is greening up as the summer progresses. For every 1,000 feet of elevation gain, the temperature decreases by about 5.5 degrees. That means that summer arrives one day later, and fall arrives one day earlier for every 100 feet of elevation gain.

Elk and other big game animals may get caught in corridors that take them to their winter habitat that is now developed and no longer a place for food and shelter.
Rick Spitzer/For the Vail Daily

There is also a huge temperature and moisture difference between north- and south-facing slopes. This difference in microclimate has a big impact on what types of vegetation are present. South-facing slopes are warmer and dryer because of the exposure to more direct sunlight. South-facing slopes in Eagle County are often covered with grasses, sedges, and sagebrush. North-facing slopes are more likely to have evergreens and aspens.

Hummingbirds migrating on their historic schedule, may cause them to arrive in their summer habitat only to find that many flowers have already bloomed, due to global warming.
Rick Spitzer/For the Vail Daily

There is also a large moisture difference between the slopes and the valley bottoms. Moisture moves downhill. The valley floors are also closer to the water table. The plants in these areas are more likely to be grasses and willows that provide a different food source than the hillsides.

Animals may use the south-facing slopes and valley floors for obtaining forage like grasses and sedges but move into the trees of north-facing slopes for protection from predators. They may also move from the hot south-facing slopes to cooler north-facing slopes during summer. Movement may also be from north-facing slopes into open meadows in the valley floors. Some of this movement occurs during a 24-hour daily cycle.

The mountainous terrain and elevation extremes in Colorado create a situation where the winter ranges are closer to the summer ranges. For this reason, the big game animals do not travel as far as animals in the prairies and open grasslands to find the microenvironment that they need. The migration pathways tend to be shorter and narrower. This is an advantage as the animals do not require as much energy to move from summer to winter habitats. This allows a higher survival rate during long winters.

During the winter months, several big game animals are on the move. A herd of pronghorn near Toponus in Routt County move into northern Eagle County near Burns during the winter. Elk move from high alpine areas into the meadows of Eagle County every year. Bighorn move from mountainous alpine areas to the lower south facing slopes in the winter. Mule deer also move into the south facing slopes of the county in winter

There are numerous things that these migrating animals now face that were not an issue in the past century. Some of these changes are having an impact on the survivability of wildlife.

Climate change is altering our environment in many ways. Longer summers, drought, and warmer temperatures are altering our environment in alarming ways. Some of these things have a big impact on migrating animals.

Mule deer and other wildlife have specific habitats, that are disappearing where they give birth and raise their young.
Rick Spitzer/For the Vail Daily

Some migration is prompted by changes in day length. The migration begins on or about the same date each year because of the number of hours of sunlight. The problem is that vegetation does not follow that trigger. Temperature and moisture are the plant triggers. An animal, particularly birds, that migrate may arrive in their summer environments to discover that many of their food sources have already bloomed or gone to seed. Drought is causing some of these plants to brown up earlier or not produce the nutritional value the animals need.

Higher temperatures and drought impact our forests directly because the trees do not have the moisture they need. Higher temperatures make it more difficult to maintain that moisture in leaves and needles. In addition, insects are surviving in larger quantities and attacking the trees. Pine beetles usually had only one life cycle in the summer months. They are now producing two life cycles which has a greater impact on the trees. Warmer winter temperatures do not kill the larva, so more beetles come out in the spring.

Highways and fencing erected along those highways block the migration of a number of big game animals.
Rick Spitzer/For the Vail Daily

Drought and higher temperatures are also causing more wildland fires. These fires are often more severe. Lodgepole pines, and some other evergreens, have serotinous cones that put down seeds during a fire. In the following years, the forest begins to recover with pine seedlings producing a new generation of lodgepoles. However, a second wildfire will kill those seedlings. They do not yet have cones. After the second fire there are no seeds and the ability of that forest to recover has changed, probably forever.

Animals need to be able to move within these seasonal ranges to respond to changes in habitat conditions and changing pressures on the landscape. Humans are altering this ability to move in huge ways. We build homes, commercial buildings, parking lots, recreational areas, and fences that prohibit animals from moving in their traditional ways. They cannot get to their preferred habitat.

The valley along the Eagle River has very little habitat left for use by wildlife.
Rick Spitzer/For the Vail Daily

Their preferred habitat is being altered as well. There is nowhere to go. More people are recreating in the winter and that disturbs wildlife. Multiple adverse threats are often compounded resulting in a huge negative impact to wildlife populations. Animals that are blocked from using their preferred habitat may simply die off.

Wildlife crossing structures, radar detection systems, signage, removing unneeded fencing, buffer zones, and seasonal closures may help maintain wildlife population. The problem is that they can be very expensive solutions and difficult to police. In addition, many areas are so developed there is no room for a corridor. Those corridors may lead to a historical critical habitat used by wildlife in the past, but those sites are now developed and no longer available.


What can you do?

  • Do whatever you can to reduce your environmental impact
  • Refrain from disturbing wildlife, especially in the winter
  • Respect closures that protect animal’s winter habitat, nest sites or birthing areas
  • Watch speed when driving, especially during dawn and dusk — vehicle collisions are deadly for wildlife and people
  • Keep your dogs on a leash to prevent them from disturbing wildlife
  • Stay on trails, as social trails can ​cause erosion, damage plants,​ aid in noxious weed dispersal, and disturb wildlife
  • Support programs and investments in wildlife protection and conservation
  • Get involved in activities that protect critical wildlife habitat and corridors

Support Local Journalism