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Online Programs: Wildlife in Winter

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Winter Ecology Concepts

What challenges does winter bring?

In mountainous regions, winter is characterized by snow, wind, cold, difficult travel, lack of shelter, and scarcity of food and water. Take a moment to think about how people respond to cold and snow. Do they head south for the season? Hole up inside? Consume foods higher in fat? Animals respond similarly to the challenges of winter.


How does wildlife respond?

During the harsh winter months, animals respond in a variety of ways to minimize energy and heat loss. Much of this energy loss results from a scarcity of food or the low nutritional value of available food. The amount of energy consumed by an animal should equal the amount of energy it expends in keeping warm, obtaining food, and avoiding predators. To keep this equation in balance, animals may adapt, hibernate or migrate in order to become more resistant to winter conditions.


What is adaptation?

While some animals migrate or hibernate, others adapt in order to resist the stresses of their surroundings. Animals may minimize the threat of winter through an interesting variety of physiological and behavioral adjustments or changes. Physiological adaptations aid mammals in dodging predators, moving with agility, obtaining food, and keeping warm. The snowshoe hare and the ermine change fur color from brown to white, better camouflaging themselves against predators in a snow-covered landscape. The large feet of the snowshoe hare and the lynx allow them to “float” on top of snow, as if wearing snowshoes. The large skull of the bison enables it to plow the snow aside when feeding.

Behaviorally speaking, small mammals may “aggregate,” or group together. In winter, deer mice become communal nesters, balling up with other mice, thereby reducing heat loss. Elk will “yard-up,” or herd together to reduce heat loss from the cold winds and to benefit from the effects of numerous animals trampling the snow. Trampling exposes vegetation and creates greater ease in foraging.


What is hibernation?

While some mammals migrate, others undergo an extended period of dormancy called hibernation. Warm- blooded mammals normally maintain a body temperature independent of the surrounding atmospheric temperature. Maintaining a constant body temperature demands much more energy when it is cold outside. Hibernation involves entering a state of dramatically reduced metabolic rate and activity. In this state, body temperature drops below normal and all bodily functions slow down. Energy savings From this reduced state of activity are extraordinary and the survival rate of hibernators is high.
Hibernators include jumping mice, ground squirrels, bats and marmots. While bears are often thought of as hibernators and do enter a reduced rate of activity, they are not considered “true” hibernators. Bears go into a state of torpor or sluggishness from which they periodically awake, and on warmer days even leave their dens in search of food.


What is migration?

Migration is the process of moving from one place to another in order to find surroundings more suitable for survival. For some species, leaving their territory is worth the energy expended in travel.

Many bird species migrate great distances. Migrating over land, however, requires approximately ten times more energy than flying. Mammals generally do not migrate to avoid winter, but there are several exceptions to this rule. Migratory mammals include caribou, some bat species, and marine mammals.Many mammals in the Greater Yellowstone Ecosystem make short migrations to more suitable living conditions at lower elevations. In the Jackson Hole area, thousands of elk leave the mountains, descending approximately 60-110 kilometers and up to 4,000 vertical feet into the valley, where they can forage more easily in shallower snows and can gain a herding advantage in the harsh winter wind and cold. Likewise, bison, bighorn sheep, and moose move to lower elevations during the winter months.

Field Guide Information for animals represented in Wildlife in Winter

Bison

Identifying Features
Height: 5′ – 6.5′
Weight: 800 – 2000 lbs.
General: dark brown coat; massive head with shaggy beard; horns; large hump protruding from shoulders; long, shaggy hair on shoulders and front legs; small tail with tuft at the end; in both sexes, short black horns curving out, up, and in againHabitat:
Open plains; grasslands; sage flats

Feeding: Grazing animal, feeds mostly on sedges and grasses. During the winter, they will push aside snow with their large head and hooves to forage.

Behavior: Bison are active during the day, but particularly during the early morning and late afternoon. In the spring, bulls band together in small groups while cows and calves collect in separate groups. Typically herds will consist of 4-20 animals, but during the cold winter months, herds upward of several thousand may join together. Such herding is beneficial during the wintertime as mass numbers of bison trample snow, making forage easier to obtain and minimizing convective heat loss.

Bison are excellent swimmers, primarily due to their buoyancy, so their heads, humps, and tails remain above the water’s surface.

When frightened, they may stampede and reach speeds of 32 mph. Primarily a plains animal, the bison wallows in dirt, creating immense 8’ x 10’ depressions that are 1’ deep. Rolling in dust and mud relieves them of itchiness and irritation, and protects their fur against insects.

In July, bulls begin to battle and gather harems of cows for mating season. Battles involve charging one another with heads down and horns facing their opponent, continuous head-butting, until one gives up. Bulls collect harems of 10-70 cows and breed with these females repeatedly during the 24 hours in which they are in heat. Gestation lasts approximately 9-10 months, followed by the birth of one calf, and occasionally two.


Moose

Identifying Features
Height: 6′ – 7 .5′
Weight: Males/Bulls 850-1400 lbs. Female/Cows 600-800 lbs.
Antlers: Mature males have large flattened “palmate,” velvet covered antlers with small “tines” or points protruding from them. Bulls shed the velvet cover off their antlers in late summer and begin to drop their racks in December. Antler spreads can reach up to 6.5 ft., averaging 77 lbs.
General: Largest member of the deer family-Cervidae. Dark brown to black with long gray legs. Long, overhanging snout. Dewlap, a “bell” of skin and fur, hangs from throat.

Habitat: Aspen stands, willow thickets, and river bottoms. Woodlands with marshes, lakes, and ponds.

Feeding: Moose are considered “browsers,” meaning they nibble on leaves and twigs. During the winter, their diet mainly consists of buds, twigs, bark, and leafy vegetation. During the summer, they rely primarily on aquatic vegetation as their food source.

Behavior: Moose are primarily crepuscular, meaning active at dawn or dusk. In the summer, moose are solitary creatures; however, during the winter, they form groups of 5-10. Moose can survive deep snow but will commonly migrate to lower elevations where depths are shallower. Such seasonal migrations may affect the size of their home ranges, but typically, moose range between 2-4 square miles.

Mating occurs in early fall, before bull moose shed their antlers. Mating behavior consists of urinating and rolling in wallows. Using their antlers for sparring, they fight for the privilege of mating with a female. They typically mate with more than one cow. Following an eight-month gestation period, calves are born in late spring, at which time the cows drive off their yearlings for seclusion in birthing. Females first breed between two and four years old. Moose life spans average 20 years.


Gray Wolf

Identifying Features
Height at Shoulders: : 26-32 inches tall at shoulder
Weight: Male = 90-110 lbs.; Extreme range = 45-175 lbs. Female = 80-90 lbs.; Extreme range = 39-125 lbs.
Length: Male = 5-6.5 ft. from nose to tail tip Female = 4.5-6 ft.
Color: Ranges from white, brown, gray, and black

General: Largest member of the dog family, Canidae; likely to be the direct ancestor of the domestic dog; long legs; deep narrow chest; large feet, front slightly larger than hind; blunter snout than coyote. With its long legs and deep narrow chest, the wolf is supremely adapted for far-ranging travel. The large surface area of the feet facilitate swift, graceful movement over snow and crust in the wintertime, granting the wolf a distinct advantage in preying on heavier ungulates.

Feeding: Wolves rely largely on ungulates for their prey-base year-round. Elk, moose, and deer comprise their principal diet in northern Montana. Nonetheless, when snow is not present, wolves also depend on smaller mammals such as beavers, marmots, ground squirrels, snowshoe hares, pocket gophers, and voles. In regions where beavers are not very abundant, ungulates constitute 90% of the biomass consumed by wolves.

Behavior: Howling and scent marking comprise two critical means of communication for wolves. Howling can occur at any time of day, and wolves may be heard howling alone, as well as together. Lone howling and social howling may communicate different messages.

Solitary wolves have been known to howl when separated from the group in an effort to locate their companions. Able to recognize other pack members’ voices, the lone wolf will call out and wait for a response. Pack members will continue howling back to the separated relative until he or she reunites with the family. When wolves in separate packs need to communicate their location or intention, howling is also beneficial.

Among the pack, howling signifies identification, location, and the assembly of separated pack members. This language also proves integral to moving pups and adults from one gathering site to the next. Through group howling, wolves reaffirm their pack bonds. This chorus commences as one wolf, typically the alpha male, raises his head to the sky and begins to sing. Soon after, other pack members join in excitedly, shoulder to shoulder, bodies wiggling, and tails wagging. Each individual member of the pack voices a unique note to produce a chorus of various sounds. The ceremony of togetherness may take place prior to a hunt in an effort to encourage the pack toward cooperation in taking down prey. A celebratory howl can follow a successful hunt as well. Finally, group howling may advertise a wolf pack’s territory and aid in its defense of that territory.

Scent-markings constitute another important means of communication among wolves. Through scenting the environment with urination or defecation, the animal can communicate a great deal to its own pack-mates, as well as to foreign packs. Scent marks enable a wolf to indicate its territory, positioning in hierarchical dominance, location of food, and even the behavioral or physiological condition of the animal.

Social Organization: A “pack” is the basic social unit of a wolf population. It may contain between 2 and 30 animals. Averaging approximately 10, the group typically forms around a mated pair of wolves which develop a pair bond, breed, and produce a litter of pups. At the core of the pack lies the dominant, “Alpha,” male and the “Alpha” female. Other members of the pack are usually their offspring and form tight social bonds with one another and with the dominant pair.

The Alpha pair are frequently the eldest members of the group and have demonstrated the greatest experience in hunting, defending territory, and various other group-related activities. The remaining members of the pack continually display their subordination to the Alpha pair via submissive posture and expression. As young subordinates approach sexual maturity at two years of age, they may challenge the dominant animals and potentially change their social position within the pack.

Breeding: Breeding typically only takes place between the Alpha pair and occurs from late January until April. Wolves habituating higher latitudes generally breed later. A few weeks prior to giving birth, the pregnant female begins preparing a den for her family. A rock cave, a hollow log, an abandoned beaver lodge, or a burrow in the sandy soil, are all likely locations for this den site. Some dens are utilized by the same packs year after year.

After a 63-day gestation period, many pups are born in late March to May. Litter sizes generally range from 4-7 pups. In the late 1900s, the average litter in Yellowstone National Park was 7 pups. During the first month of the pups’ lives, they never leave the den, and the mother is the only pack member with whom they have contact.

As soon as they leave the den, the entire pack begins to look after the pups. Pups are able to venture forth from the den at 8-10 weeks of age and are then moved to a “rendezvous site” which becomes the new meeting place for pack members, as well as a home base for the pups. While the older pack members are out hunting at night, one relative, called the “pupsitter,” remains with the pups at the site. Each morning the group returns to the rendezvous site where they remain all day resting and playing with the pack. After two to three weeks in one rendezvous site, the pack is likely to relocate this spot nearer to prey.


Elk

Identifying Features
Height: 4 – 5’
Weight: Males/Bulls 700-1000 lbs. Females/Cows 500-600 lbs.
Antlers: Bull elk grow antlers in late spring and early summer and typically shed them in April. Spreads can reach up to 60-74 inches and 40 lbs. Healthy adult males average six points, or tines, per antler beam.
General: A large member of the deer family with a reddish brown body, a cream-colored rump patch, and a darker head, neck and legs. Males often have a paler coat than females.

Habitat: In the summer, elk generally inhabit forests and meadows at higher elevations. In the winter, they migrate to lower elevations. Typically they rest in forested regions during the daytime and graze in the meadows at night. They are widely distributed in Jackson Hole, Wyoming where they are drawn toward “ecotones,” or transitional regions between plant communities, or vegetative cover. The severity of winter brings many elk into the valley. Much of this land is designated National Elk Refuge land, offering the elk a higher degree of protection during hunting season and supplemental feeding when snow depth impedes foraging effort.

Feeding: Elk graze more heavily than they browse, but they will eat leaves, twigs, and the bark of aspens and other deciduous trees, as well as grasses, forbs, herbs, and shrubs. During the winter, many elk migrate to feed grounds when forage is difficult to find. The National Elk Refuge in Jackson, Wyoming has incorporated supplemental feeding into their management program beginning in 1912 feeding the elk hay. In 1937, the Refuge began feeding baled alfalfa, and today, the United States Fish and Wildlife Service feeds the elk alfalfa pellets for a few weeks to a couple of months each winter. Elk process their food through rumination or cud chewing, a trait of the entire deer family.

Behavior: Elk, or “wapiti,” are primarily nocturnal but most active at dawn and dusk. During the summer, mature bulls separate into bachelor herds, while cows and calves herd with one another. Breeding season begins in late summer/early fall, and this period introduces a new social grouping of elk, as each mature bull rounds up his own harem of cows.

During the breeding season, or “rut,” bulls exhibit a variety of behaviors in attempt to gather mates and to deter competitors. They wallow in mud, thrash about in the brush, and spar with rivals, rearing up and locking antlers. Aside from such aggressive displays of dominance, bulls also compete by calling out in a sequence of high-pitched notes. This mating call is referred to as “bugling.” These combined efforts enable dominant, mature males to accumulate and defend harems of up to 60 cows. Eligible females include cows at least 2.5 to 3 years old.

After mating, females have an 8.5-month gestation period, typically giving birth to one spotted calf in the spring. Calves can walk within a few minutes of birth. Cow elk will nurse their young for a month after birth.


Red Fox

Identifying Features
Weight: 10-15 lbs.
Length: Head and body 22”-24”; tail 14”-16”
Color: Many color variations but predominantly reddish-yellow, darkest on shoulders; belly white; tail scattered with black hairs and a white tip; black feet; back of ears black
General: Size of a small dog; narrow snout; pointed ears; bushy tail

Habitat: Widespread; mixed cultivated and forested area; open country; brushlands; streamsides

Feeding: Voles and mice comprise the bulk of their diet, but the Red Fox will also eat birds, rabbits, squirrels, other small mammals, insects, and fruits.

Behavior: Late afternoon through early morning is the most active time for the red fox. Male home ranges vary between one and three square miles. Predominantly solitary mammals, foxes are shy and cautious with the exception of breeding season. In the winter, a female, or vixen, will mate with a male and together form a family unit with their kits.

An average of four to eight kits are born in a den each spring when both the male and female share the responsibilities of rearing their offspring. Typically, foxes will locate an abandoned badger or marmot den, or dig their own on a slope with open views. Both adults bring food to the den for about a month until the kits are ready to leave. Kits remain with their parents until the following fall when they are prepared to venture off on their own.


Snowshoe Hare

Identifying Features
Weight: : 2-4 lbs.
Length: Head and body = 13-18 inches long. Females, “does,” are larger than males, “bucks.” Ear length: 2.5-3.5 inches
Color: Summer – dark brown with black-tipped ears Winter – white with black-tipped earsGeneral: Long ears, long hind legs, large feet, soft fur, short tail, large and laterally positioned eyes

Habitat: Swamps, riparian areas with willows and thickets, and boreal coniferous forests with dense undergrowth

Feeding: In the summer, hares feed on grasses, green vegetation, willows and berries. In the winter, they feed on conifer buds and the bark of aspen, alder, and willow. On occasion, they eat meat and can irritate trappers by stealing their bait.

Behavior: Snowshoe hares forage at night and typically remain hidden, bedding down among bushes during the day. Their molting (coloration change) and camouflage enables them to remain active throughout the year. The changing pelage is initiated by a shift in photo-period, or length of daylight. As daylight decreases in autumn, hare begin to grow a white-tipped winter coat. Splotchy at first, hares blend in nicely with the patchy snow cover. By the time the ground is fully covered, the hare has turned completely white.

The snowshoe hare avoids open expanses of land and often runs among the bushes. It can bound up to 12 feet in distance and run up to 30 mph. Hares avoid water, opting for dust baths instead. The home range of the non-territorial male hare averages 3-10 square miles, often overlapping with the ranges of several females.

In courtship display, males drum the ground with their large hind feet, chase females, and leap into the air while urinating on them. They breed between the spring and early summer of their second year. Females have a gestation period of five to six weeks and annually yield two to three litters of one to six offspring each.

Like most leporid populations, meaning the rabbit and hare family, the Snowshoe Hare population is especially cyclic, skyrocketing and plummeting every nine to ten years. Because leporids reproduce so rapidly, they can achieve extremely high population densities in brief peiods of time. It is theorized that the consequent crowding initiates the “stress syndrome,” which is thought to retard the reproductive process and to stimulate a dramatic decline in population. Weasels, foxes, mink, owls, hawks, wolverines, bobcats and lynx are known to prey on rabbits. Hares can live up to eight years in captivity and three in the wild.


Mountain Lion

Identifying Features
Height at Shoulders: 26-31”
Length: head and body, 3.5’-4.5’; tail, 2.5’-3.0’
Color: yellowish to tawny or grayish with buff below; dark brown on tip of tail, back of ears, and the sides of its nose; eye shine greenish-gold Other names: “cougar,” “puma,” “catamount”

Habitat: The mountain lion is highly adaptable and inhabits a variety of terrain including forests, open woodlands, swamps, and semi-arid mountainous terrain.

Feeding: Mountain lions chiefly feed on deer but also eat coyotes, porcupines, rodents, hares, and occasionally domestic animals. Typically, they will kill one deer a week, but on occasion, they have been known to slaughter several deer or an entire flock of sheep in one night. After making a kill, cougars will often cache portions of meat to consume later.

Behavior: Mountain lions are solitary and strongly territorial mammals that require undisturbed or isolated tracts of wilderness. As solitary predators, these skilled hunters rely heavily on the remarkable adaptations that allow them to stalk noiselessly. Retractable claws, spongy toes, central pads, and hair that covers the bottom of the paw, all contribute to stealth. Speed is essential in its predatory efforts and is made possible through long legs, digitigrade locomotion (walking on toes, not using the heel), and a flexible spine. Digitigrades are animals that walk on their digits, or toes, such as dogs and cats, thereby lengthening their legs significantly. The flexible spine enables the back to curve severely and the hind legs to reach beyond the front legs while running.

Mating season is not fixed for mountain lions. After an 88-97 day gestation period, kittens are typically born in a den lined with vegetation or moss in a rocky crevice or otherwise protected spot. Females have a litter of 1-6 kittens who remain with her for one year. Kittens are ready to breed at 2-3 years of age and can do so every 2-3 years thereafter.



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