In the shadow of ancient and dense pine forests, a sage-grouse burrows beneath a blanket of deep snow. Guided by gleaming starlight, a snowshoe hare drifts through the frost-covered grasslands like a snowy spectral—swift-footed and sure. Its large feet distribute its body weight over the surface and its hollow white hairs—which contain air instead of pigment—keep it well-insulated. The icy luminance cast by the moon shimmers with the rising sun and reveals snow-dusted boulders of slumbering bison. Their vaporous breaths swirl in the air with each exhale and sink into the steam of nearby hot springs.
These hydrothermal features are a surface expression of the deep magmatic forces below the frozen Earth. They shelter thermopiles (heat-loving microorganisms) that thrive in the alkaline pools, sulfuric cauldrons and bubbling fumaroles (steam vents). Single-celled communities of cyanobacteria obtain energy through photosynthesis and, in turn, grant the Grand Prismatic Spring at Midway Geyser Basin its vibrant colors. Bison, moose, elk and geese wade in thermally influenced wet alpine meadows and snaking streams—grazing on vegetation and seeking respite from winter’s chill.
To combat the cold, conifer trees retain their needles, extending their ability to photosynthesize. Aspens and cottonwoods photosynthesize before they produce leaves with the aid of chlorophyll stored in their bark. Every resident animal, plant and microbe species in the Greater Yellowstone Ecosystem evolved over millions of years to endure the extreme elements through behavioral, morphological, physical, biochemical and physiological adaptations.
The Greater Yellowstone Ecosystem encompasses an area between 12 and 22 million acres. The region spans portions of Wyoming, Montana and Idaho and contains extensive climatic and elevational gradients—making it one of the largest nearly intact temperate-zone ecosystems on Earth. The prairie expanse is biologically integral to myriad species—providing critical habitats and migration routes. As one of the most threatened biomes on the planet, its preservation is equally significant to Tribal nations within the Northern Great Plains, who share spiritual and symbolic attachments to the landscape.
Martha Kauffman, Vice President of World Wildlife Fund’s Northern Great Plains program, declares, “The Northern Great Plains is as important as the Amazon or Arctic, and deserves our attention.” Grasslands are responsible for sequestering and storing carbon. Destruction of these lands has an equally devastating effect as global deforestation. In 2019 alone, approximately 2.6 million acres of intact grassland were plowed and converted for row-crop production across the U.S. and Canadian Great Plains. That is an area larger than Yellowstone National Park. In the Northern Great Plains, 600,000 acres were lost to wheat, corn and soy production.
In June 2021, the United States Geological Survey (USGS) Northern Rocky Mountain center released the Greater Yellowstone Climate Assessment in collaboration with scientists, resource managers and Tribal communities from Wyoming, Montana and Idaho. The report analyzed climate trends in the Greater Yellowstone Ecosystem from 1950 to 2018, revealing illuminating information about how these changes could progress by 2100 based on various greenhouse gas emission scenarios. According to the data projections, if future emissions are not mitigated, Bozeman, Montana and Jackson, Wyoming will be subject to 40‒60 more days per year exceeding 90℉.
Annual monitoring data suggest consistently dry, warm years could diminish 40 percent of the Greater Yellowstone’s wetlands. Declines in water levels could affect species that are dependent on wetlands for survival, such as moose, beaver, trumpeter swans and sandhill cranes. Another repercussion of higher temperatures is less soil moisture, which would place significant stress on plant communities and impact the dietary quality of browse species. Reduced plant productivity impacts the carbon sequestration potential of landscapes, affects hydrologic flow paths and water storage within floodplains, reduces wildlife viewing opportunities and removes natural barriers to wildfire outbreaks. The Greater Yellowstone Ecosystem is one of our planet’s last large landscapes and one of Earth’s last wild places. It urgently needs protecting.
Greater Yellowstone is home to the largest concentration of mammals in the lower 48 states. Predator and ungulate (hoofed herbivore) species include the gray wolf, bear (grizzly and black), plains bison (buffalo), moose, and elk. The sheer diversity and distribution of species positions Yellowstone as prime territory for observing the complexities of predator-prey dynamics.
At the very top of one trophic system is a mammal called Drew McCarthy. This species is a year-round resident of the Greater Yellowstone region—qualifying him as a most adept Expedition Leader for Natural Habitat Adventures. In his webinar, McCarthy examines the following survival strategies: resistance, migration, and hibernation; and how climate change influences animal behavioral and biological adaptations.
In contrast to top-down trophic systems, bison (“iinniiwa”: Blackfoot, “tatanka”: Lakota, “ivanbito”: Navajo, “kuts”: Paiute) influence natural systems from the bottom-up, which makes them a keystone species. As the largest land-dwelling mammal in North America, bison exhibit the ability to transform the landscape simply by engaging in their typical behavior each day. Comparable to how elephants engineer the African savanna by clearing forest cover and germinating seeds through dung droppings, bison are the eco-engineers of America’s savanna.
Bison play critical roles in shaping the biodiversity of open grassland communities. All of Yellowstone’s 67 mammal species have benefited from bison in one form or another. During the winter season, bison perform an array of ecosystem services. Their elongated vertebrae—to which strong neck muscles are attached—enable the mammal to sweep its massive head from side to side to clear off up to three feet of snow. Deer, elk and smaller animals like fox and prairie dogs save critical energy by traveling through these bison-paved highways.
Bison also influence how the spring season blossoms through the valleys and mountains of the Greater Yellowstone Ecosystem. Through grazing, bison keep the grasses short and nutrient-dense. Grazing may appear to be a destructive process within the environment, but it actually preserves soil moisture, increases the rate at which nutrients are recycled back into the Earth and stimulates productive plant growth. The non-uniform yet repetitive grazing patterns of bison, and the intensity at which they graze, turn back the clock on forage green-up (progression of plants emerging), allowing for a longer and more fertile spring. And with up to eleven hours a day dedicated to foraging, it’s easy to imagine how verdant these landscapes can become. The excess of young plants that spring up from grazing is also advantageous to Yellowstone’s free-ranging and migratory wildlife, which collectively consume as much as 35 million pounds of plant matter each year.
Moose (Alces alces) are the largest member of the deer family, and their size is precisely why they are one of nature’s most resilient cold-climate species. Their adaptive mechanism to conserve body heat is best described by a zoological principle known as ‘Bergmann’s Rule.’ The rule applies to the ratio of body surface to weight in warm-blooded animals. Moose have a relatively small surface area compared to their volume. Regardless of external temperatures, moose maintain a relatively constant internal temperature (homeothermy)—meaning they require only minor metabolic and environmental adjustments to live comfortably in Yellowstone’s lowest temperatures. In addition to an insulative coat that sheds moisture and wind, moose have a long and cavernous nasal passage that prevents evaporative heat loss. The chambers in the sinus cavity cool and condense moisture with each exhale, allowing the moose to retain both energy and heat
In the park’s southwestern corner and in the Soda Butte Creek, a solitary moose may be spotted grazing on aquatic plants such as water lilies and duckweed or making use of their impressive stature to tear off twigs high in the willow trees. An adult moose will eat as much as 44 pounds of food each day in the winter. Moose thrive in this winter wonderland, but climate change is straining their ability to self-regulate during other seasons. Higher external temperatures push moose to the upper limits of their thermoneutral zone, which is defined as the range of ambient temperatures without regulatory changes in metabolic heat production or evaporative heat loss. Fewer than 200 moose remain in Yellowstone. Their decline in population can be attributed to the loss of old-growth forests beyond the borders of the park, hunting across the boundary lines, and ravenous wildfires.
In the United States and throughout the world, summers are becoming dryer and hotter. Fire activity has therefore increased in frequency and severity, compromising forest health and resilience. Moose in the Greater Yellowstone Ecosystem rely on mature conifer forests for their wintering habitat. The more spruce and fir forests that become decimated in blazes, the less likely moose will be able to survive the West’s harsh winters. Warming temperatures are also contributing to an uptick in tick populations, which put significant stress on moose by causing blood loss, reducing reproductive success and lowering the survival rates of newborn calves.
About half of the wolves in Yellowstone display a black coat, while the other half more closely resemble their nomenclature. Biologists have observed that the black-coated wolves are less aggressive than the gray-coated wolves, which is a survivorship advantage when territorial conflicts arise. Interestingly, there is superior mate choice between male and female pairs of opposite coat colors. Wolves have both a fur undercoat and an overcoat. The thick undercoat traps heat, which helps wolves regulate their body temperature. The overcoat consists of hollow and coarse insulative hairs. This combination of layers enables the wolves to stay active throughout the winter months. Wolves take advantage of deep snow to prey upon long-legged, small-footed ungulates, which are less agile in extreme winter conditions. However, warming temperatures mean a decrease in annual snowpack, which may decrease wolf hunting success.
The best time to see wolves is the peak of winter, and the Lamar Valley of Yellowstone’s northern range is the best spot on the planet for wolf viewing. The wide-open expanse is lined with trees covered in glittering ice crystals. The snow lays thickly drifted on the sloping hills and can be heard falling faintly through the park and faintly falling on a prowling wolf pack, which stands out in sharp contrast against the sea of white.
Nat Hab has a dedicated team of professional naturalists and biologists who possess intimate knowledge of wildlife behavior. Their constant communication with local wolf researchers grants travelers unparalleled access to wolf locations and activity. Despite the millions of visitors who scour through sage and shrubbery each year, WWF and Nat Hab’s Ultimate Wolf & Wildlife Safari ensures private experiences and close encounters with Yellowstone’s most elusive predators.
The elk (Cervus Canadensis), also known as the ‘wapiti’ by Native American populations, are the most abundant large mammal found in Greater Yellowstone. Yellowstone National Park shelters approximately 10,000-20,000 elk during the summer months and fewer than 4,000 in the winter. In winter, colder temperatures and snowfall decrease the amount of forage that grows. This forces many ungulates to migrate in order to increase their access to high-quality food. Elk travel to the northern range and around Gardiner, Montana, and south to the Jackson Hole Elk Refuge in Wyoming.
Though elk make up more than 85 percent of the wolves’ winter diet, herd size and distribution face a much graver threat—climate change. As a migratory ungulate species, elk mothers and calves are disproportionately affected by volatile conditions. There is, unfortunately, but one herd (Madison-Firehole) that resides in the park during both winter and summer, so research on reproduction and survival is limited. Thus far, studies have conclusively determined that environmental variability plays a role in food accessibility and nutritional content. Warmer temperatures stimulate plant growth and accelerate green-up, which in turn causes a shorter growth cycle. Consequently, there is poor synchronization of calving with peak plant nutrition—resulting in lower fat reserves and an associated high mortality of newborn elk.
The third adaptive strategy is hibernation—or more accurately—torpor. Torpor is the most effective means of energy conservation available to mammals. This physiological suppression of metabolic rate—often accompanied by suppression of feeding behaviors and defecation—is an adaptation of endothermic vertebrates that enables them to survive the energetic demands of cold ambient temperature and limited resources.
The American black bear (Ursus americanus) is an archetype of this adaptation. The Greater Yellowstone Ecosystem is one of the few regions south of Canada where black bears coexist with grizzly bears. Though smaller than grizzlies, black bears still require mass quantities of vegetation to stimulate their winter torpor. Black bears have a broad thermoneutral zone but require substantial energy input in order to maintain their internal body temperature. The fall season is a critical time for bears to feed on berries. Bears have an elongated digestive tract, which allows for more efficient digestion of vegetation. To maximize the quality of vegetal food items ingested, they typically forage for plants in phenological stages (periodic biological phenomena) of the highest nutrient availability.
After black bears have built up sufficient adipose (fatty) tissue and have grown thicker fur, they retreat into dens constructed out of fluffy, insulative material. Though these wintering habitats shield the bears from freezing temperatures and harsh winds, they fail to protect the animals from the consequences of climate change. Longer summer months delay typical foraging and denning behaviors. As a result, black bears are more active during the day—increasing their chances of coming into contact with humans and causing conflicts over food and territory.