A Yellowstone Winter
It’s deep winter in Yellowstone and the evening air is crisp and still. My breath hangs in the last weak rays of the sun which is setting behind the trees to the west. The crusty snow creaks under my boots. Occasionally, I break through to deep fluff and fight back to the top. I stop to listen. Absolute silence. The temperature is dropping so fast that all the forest seems to be holding its breath. I am near the road now and relish the thought of a warm car. In winter, simple pleasures become lavish delights. A warm meal, a mug of dark beer, a gathering of friends around a fire, these are the rarely counted blessings of modern life. But winter for most animals is an epic struggle for existence that only slows with the spring thaw. In Yellowstone, this is a time of tension and hardship, of using every adaptation, every calorie and sinew in efficient, calculated operation.
Wolves are supremely adept at surviving the harsh winters of Yellowstone. The grey wolf (Canus lupis) is a native to Yellowstone Park and well adapted to handle the cold. Wolves hunt in larger groups in the winter, which is more efficient and uses less energy than hunting individually. In addition, the previous year’s pups are now able to hunt and anxious to participate in pack duties. Pooling their efforts, they bring down bigger game, which allows the weaker pack members to eat as well.
Hunted, poisoned, and trapped to near extinction by every means available including the U.S. government, the wolves have been quick to recover. In January 1995, 14 wolves were reintroduced to the park, and 17 more a year later. After just five years, there are about 120 wolves in the Yellowstone ecosystem in 14 packs. They are considered to be thriving and are slowly changing the face of Yellowstone.
Bloody carcasses of elk and moose throughout the park are telltale signs of the wolves’ handiwork. Before the wolves were reintroduced, elk had few predators as they are too fast for grizzlies to catch and too big for coyotes to bring down. There was a gap in the predator lineup for over a century in the park. Wolves fit the bill perfectly, being both large and fast enough to bring down elk and moose. The wolves cull the weak from the herds leaving the stronger ones to breed.
“I think the most noticeable thing around Yellowstone Park was every five or 10 years, you'd have these big winter die-outs. You'd have elk herds with very high numbers that contained a lot of old decrepit sick animals. And they would hang on and hang on. So when you got a bad winter, literally thousands of them would just die from starvation. The vegetation was being used by animals that were no longer reproductively active.”
Ed Bangs, Wolf Recovery Coordinator
U.S. Fish and Wildlife Service
Wolverines, foxes, eagles, and other carrion eaters feed on the leftover carcasses that were a rare treat until now.
Wolves are well suited for the cold climate and deep snows of Yellowstone in winter. Their adaptations read like a wish list of winter survival skills:
•Thick coat of water-repellant guard hairs with a
downy underlayer
•Stamina enough to cover 50–150 miles a day
•Keen eyesight, hearing, and a sense of smell a hundred times more sensitive than ours
•Operate in packs to increase odds
•Unique body temperature regulation
But, it is the wolf pack itself that really makes wolves unique. Pack hierarchy is very complex and brutally reinforced. It is not uncommon for members to attack their own, sometimes even killing them. Led by an alpha pair, the pack moves, hunts, and mates through an elaborate communication system. From howls and barks to body position, eye contact, and tail position, they relay important information, warn of strangers, and signal danger. This helps them in the hunt as they move in on prey. With military efficiency, they stalk, surround, and attack. One goes for the mouth or nose while others tear at the legs and heels, tearing and nipping at its flanks. Once the prey is down, each wolf eats in order of its rank in the pack with the omega (the lowest) getting the scraps. This systematic and calculated efficiency in killing has made the wolf feared and despised by man.
Elk are one of the most numerous ungulates in the park (about 20,000 in the winter) and have been in the national spotlight since the early 1930s. For thirty years, elk, pronghorn, and bison numbers were artificially controlled by shooting or trapping. In the 1960s, based on new studies that suggested ungulate populations could possibly be self-regulating, they stopped killing elk. According to the National Park Service, "protein content of grasses, yearly growth of big sagebrush, and seedling establishment of sagebrush were all enhanced by ungulate grazing." However, the belief that elk grazing was damaging to the vegetation in the northern wintering range and that grazing accelerates erosion, although not supported by research data and analysis, has persisted.
In winter, elk move north to warmer, open meadows of the winter range away from the deep snows and freezing temperatures of the park’s southern mountainous plateaus. With long, powerful legs and thick coats of hollow hairs they brave the cold in vast herds. By winter, the bulls’ antlers are hard and shiny and show the scars from defending their harems in rut. When they drop in March or April, rodents will chew them for much-needed minerals. The elk congregate in open meadows where grasses are easily exposed and water is near. To get at the grasses, they paw the ground with their hooves, but when the easier food has been eaten or is too hard to attain, elk will begin to forage on shrubs, pine branches, even the bark of trees.
Elk have good hearing, eyesight, and an acute sense of smell to alert them to predators. The thick-tined antlers and sharp hooves of a healthy bull offer considerable defense against the opportunistic wolf. With a bleat from one of the herd, the massive brown elk are able to move gracefully and quickly through the woods for cover. Many a frustrated hunter can tell you how amazingly fast these animals can move when alarmed.
Like elk, buffalo have been native to the Yellowstone area since prehistoric times, though rampant "hunting" (read slaughter) reduced them down to only 50 around the turn of the century. After years of importing and management, the numbers reached a high of 3,500 bison in 1996, but 1,100 were killed over the next year to control spreading brucellosis to beef cattle.
Brucellosis causes cattle to abort their fetuses but has never been shown to have been spread by buffalo. Despite the very low risk to humans and livestock today, the possibility of contagion exists. Therefore, the state of Montana believes its "brucellosis-free" status may be jeopardized if bison are in proximity to cattle. Although the risk is very low, if cattle become infected, ranchers can be prevented from shipping livestock out of state until stringent testing and quarantine requirements are met. Scientists are studying new possibilities, but there is yet no known safe, effective brucellosis vaccine for bison. This hot subject brings Montana and Yellowstone to the forefront of national news every year and still lacks an acceptable solution.
Bison are the largest mammals in Yellowstone National Park and are strictly vegetarian. They graze on the grasslands and the meadows, the foothills, and even the higher, forested plateaus to the south. Bulls can weigh up to 1,800 pounds, while cows average about 1,000 pounds. Both stand about six feet tall at the shoulder, and can move with surprising speed to defend their young or when approached too closely by people or snowmobiles. Every year a few snowmobilers find out that a ton and a half of buffalo, even with its seemingly lethargic demeanor, can erupt with explosive speed and ferocity.
In the deep snows of winter, they use their large heads like a plow to push aside snow and find winter food. Swinging their heads back and forth, burrowing downward, they expose the grass beneath. In the park interior where snows are deep, they winter around the geyser basins and thermal pools. They gather around the meadows where hot steam rises from the numerous geothermal spots (Yellowstone has more than the rest of the world combined). Despite the bison’s thick, scraggly fur that traps heat in, they usually move, like elk, to winter range in the northern part of Yellowstone when the snow gets deep.
Winter is a quiet time in Yellowstone Park. Besides the occasional whine of a distant snowmobile, or the quiet slish-slishing of cross-country skiers, little human activity interrupts the tranquil, frozen struggles of nature here. When snow comes to the Yellowstone ecosystem, the animals make their primordial sally with nature. They struggle toward another spring and the serene complacency of summer.
