Elk Use Changing Environmental Signs to Time Migrations

Candice Gaukel Andrews November 12, 2019 0

The Greater Yellowstone Ecosystem is home to approximately 30,000 to 40,000 elk. Yellowstone National Park alone provides summer range for an estimated 20,000 elk. ©Candice Gaukel Andrews

On a recent Natural Habitat Adventures fall trip to Grand Teton and Yellowstone National Parks, my guide talked about a common question he gets from visitors who come to see the National Elk Refuge at this time of year. “Where are all the elk?” they typically ask.

Visitors tend to believe that because there is a wildlife preserve for the elk, they are there all the time. But in truth, the migrations of the Greater Yellowstone Ecosystem’s (GYE) superherds of elk are some of the most exciting phenomena in the region. The annual winter migration usually starts in late October and lasts into December, taking the elk to the lowlands to find softer snow and the food under it. The best time to see the animals in the National Elk Refuge is in winter.

Then, ordinarily, the elk make their way back to higher elevations in April and May. Calves are born in protected areas during this spring migration in late May and in June.

But what, exactly, drives this extraordinary and massive migration pattern? A brand-new study may just provide the answer.

The annual winter elk migration runs from late October until December. In the lowlands, the animals find softer snow and the food under it. ©John T. Andrews

Why the location of elk matters to so many

The Greater Yellowstone Ecosystem is one of the last remaining large, nearly intact ecosystems in Earth’s northern temperate zone. It encompasses about 18 million acres of land managed by more than 25 public entities and hundreds of private landowners. And Yellowstone National Park’s approximately 20,000 migratory elk are among the most important large mammals in that ecosystem, pulsing in and out of both Yellowstone and Grand Teton National Parks and the adjacent wilderness areas each year. Where they can be found at any given time greatly matters to wild animals and humans alike.

The abundance of these migratory elk sustains diverse carnivores and scavengers, attracts tens of millions of dollars in visitor enjoyment to gateway communities (as well as revenue to local economies through hunting outside the park), and inspires national and global conceptions of wilderness. These migrations define and unify the GYE, both culturally and ecologically.

As Yellowstone’s most abundant ungulate, elk comprise approximately 85 percent of winter wolf kills and are an important food for GYE’s threatened grizzly bears, mountain lions and at least 12 scavenger species, including bald eagles and coyotes. Competition with elk can influence the demography, diet and habitat selection of bighorn sheep, bison, moose, mule deer and pronghorn. Elk browsing and nitrogen deposition can affect vegetative production, plant diversity and soil fertility. Thus, changes in elk abundance over space and time can alter a multitude of plant and animal communities in Yellowstone.

In a new study, the migratory patterns of more than 400 elk in nine major populations in the Greater Yellowstone Ecosystem were analyzed using GPS tracking data provided by a variety of federal, state and nonprofit organizations. ©Wyoming Migration Initiative, University of Oregon Infographics Lab

But the migratory elk of the GYE are experiencing a growing number of new ecological changes and conservation challenges, such as drier and hotter summers, invasive species and introduced diseases. Understanding and management of the GYE elk migrations remains fragmentary: scientific studies typically focus on one herd at a time, management is divided among numerous agencies and public interest is fractured among more than 100 nongovernmental organizations. In fact, most people in the region have never seen a map showing the striking geographic scope of elk migrations.

And that’s why this new study is so important.

How being flexible could help elk deal with climate change

The new study, published in the scientific journal Global Change Biology in March 2019, combined tracking data from more than 400 elk in nine major populations in Yellowstone that had been fitted with GPS collars between 2001 and 2017 with satellite imagery to create a comprehensive model of what drives these animals to move. While a smattering of previous studies had investigated the migration of individual herds in the park, none before had investigated the phenomenon on an ecosystem scale.

Elk are browsers and grazers, feeding on forbs, grasses and sedges in summer and woody growth (aspens and willows) during winter. Female elk can weigh up to 500 pounds. ©Candice Gaukel Andrews

The data was then analyzed to pinpoint when each elk made its trek from its winter range to its summer range and back again, and used satellite images to infer the conditions on the ground during the journeys. The results showed that elk tended to rely primarily on environmental cues, leaving their winter ranges and setting out to their summer ranges as soon as the snow had melted and during the “green-up,” when fresh, nutritious plant growth began to sprout. Likewise, encroaching snowfall and hunting pressure cued them to make the return journey.

The research team was surprised by the extent of the flexibility of the elk: one year, a female might migrate in early May, but the next year in late July, depending on the timing of the snowmelt and green-up. So, in contrast with some other species, such as migratory birds—which rely on changing day length to decide when to move—elk use the immediate environment to choose the time to migrate.

The results of the study seem to suggest that as climate change reshapes the environment and weather of the GYE, elk have the means to adjust their migratory patterns and adapt to the new conditions. That’s likely a good thing—but, of course, there will a number of consequences because of these adaptations.

Bull elk can reach weights of 700 pounds. Only the males have antlers, which they shed in March or April. They’re territorial only during the mating season. ©Candice Gaukel Andrews

When subtle signs lead to robust ripple effects

The tracking data in this study did reveal a definite trend: elk, on average, arrived on their winter ranges 50 days later in 2001 than in 2015. This change had been noted by wildlife managers in the area but had yet to be quantified on the ecosystem scale until now. While this adaptability could benefit the survival of the elk, it will soon have ripple effects throughout the Greater Yellowstone Ecosystem and in local economies because climate change is likely to hit national parks harder than other areas of the country.

This new picture of the GYE elk migrations clearly demonstrates the need to think and operate at the landscape scale. In the future, with climate change, the altered timing of these mass movements will affect other wildlife and the people who depend on them, including predators, scavengers and humans. For park managers, this kind of research gives them incentives and options—such as protection of migration corridors and seasonal habitats—for ensuring elk and other keystone species in the Greater Yellowstone Ecosystem will persist.

Here’s to finding your true places and natural habitats,

Candy

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