By Jenny Feick, PhD
All pictures were taken by Jenny Feick unless otherwise credited.
Relatively few intrepid souls traverse the vicinity of the Great Divide during the winter months. Most thru-hikers spend from November to March planning and preparing for their trekking expeditions. Humans, if they travel on the Great Divide Trail (GDT), visit it by choice. But what about the wildlife who live near the Great Divide? How do they prepare for winter? How do they even know that winter is coming?
In wild animals, seasonal changes are tracked by the photo-neuroendocrine system, a sensitive collection of glands, hormones, and neurons that are wired to adjust an organism’s internal chemistry as the length of a day changes. Wildlife notice when the photoperiod (day length) begins to shorten in the fall. This triggers their preparatory behavior. Their choices are to leave, sleep through it, change in some way, store or cache food, or simply endure it! Then there are those who, like the grasshopper in the Aesop’s Fable “The Ants and the Grasshopper”, don’t prepare for winter at all, and have to count on the next generation to perpetuate the species.
Some creatures (besides people), migrate away from the Great Divide area to avoid the harsh winter conditions. Many birds travel south great distances while others migrate to the B.C. coast, and a few just travel to nearby mountain valleys. In summer, a GDT hiker wearing a bright red or pink hat might hear a buzz and a chip sound as a rufous hummingbird (Selasphorus rufus) dives close and hovers to see if the colourful object is a giant flower full of nectar and then dashes off in disappointment. As the short alpine flowering season ends, these tiny, fast-flying birds head south, flying over 6,400 km to southern Mexico. Starting in mid-August, MacGillivray’s warblers (Geothlypis tolmiei) leave the shrub thickets of the upper subalpine to migrate even further south, all the way to Central America.
Rufous hummingbirds fly south to Mexico along the Rocky Mountains as early as July to be sure to escape winter on the Great Divide (Photo by Larry Halverson)
One of the most amazing long distance bird migration phenomena in the Rocky Mountains involves golden eagles (Aquila chrysaetos) and up to 17 other birds of prey. Starting in September, hundreds of eagles leave their breeding areas in Alaska, Yukon, northern British Columbia and Alberta. They use thermal wind currents to efficiently fly south over the Rockies to reach their wintering areas in the southern United States and Mexico. They travel along specific corridors along the Eastern Slopes and the Rocky Mountain Trench. Citizen scientists with the Rocky Mountain Eagle Research Foundation have been tracking this extraordinary migration ever since it was noticed and monitored by naturalist Des Allen and international bird expert Peter Sherrington on March 20, 1992 at the Mount Lorette Natural Area in Kananaskiis where Des was the Natural Area Steward. Telemetry data shows that these eagles fly from 1,900 km to over 6,400 km to reach their wintering sites. Quite the thru-fly!
RMERF volunteers at the eagle watch site near Mount Lorette in Don Getty Provincial Park documenting migrating raptors in October 2022, the 30th year of the count.
Other birds sometimes seen by summer hikers in alpine tarns such as goldeneye ducks (Bucephala sp.) or in fast flowing mountain streams like harlequin ducks (Histrionicus histrionicus), do not migrate as far. Like many who enjoy the mountains in the summer, they winter on the west coast. Actually, the males head for the coast as soon as mid-June to early July shortly after the females begin to incubate their eggs. Their mates leave the mountain streams to join them in the early autumn after the ducklings have fledged and learned to survive on their own.
A Harlequin duck drake in October 2017 ready to spend the winter on British Columbia’s west coast (Photo by Brian Wesley)
Certain other birds move to lower altitudes as winter approaches. As invertebrates die out with the first frosts in high elevation areas, Townsend’s solitaires (Myadestes townsendi) head for valleys plentiful in junipers, including the upper Columbia Valley in B.C. Here they subsist primarily on the fleshy cones of Rocky Mountain, common, and creeping junipers for the entire winter until insects and spiders hatch the following spring.
Townsend solitaires spend the winter in big, dry valleys containing juniper. (Photo by Larry Halverson)
If its local alpine rivulet freezes, American dippers will also make a slight altitudinal shift to a part of their territory where they can find mountain streams that still flow quickly, enabling them to seek out the aquatic invertebrates that sustain them year-round.
As wintertime approaches in the mountains, North American porcupines (Erethizon dorsatum) descend the slopes along well-defined routes marked by debarked trees. They will either build a nest or find an overhanging rock outcrop, a hollow log, an abandoned burrow, or a stump to protect them from severe weather. They reduce the size of their home range to 80-90% of the area they use in the summer. Porcupines turn into snowplows in winter, creating deep troughs between their dens and favorite feeding areas, which tend to be within 100 metres of their winter dens. Usually nocturnal, in winter when the weather is dry, they will feed at any time of the day or night. They focus on eating the needles and inner bark of conifers, especially pine, in the winter months. When precipitation falls (snow, sleet or rain), porcupines prefer to stay in their dens. If caught outside feeding when a storm hits, a porcupine will sit hunched in a tree until the storm stops. Even though porcupines are usually solitary, several porcupines will den together to stay warm in winter. In the spring, they return up the mountainside to their summer feeding areas.
In winter, porcupines eat the nutritious inner bark of pines, like this lodgepole pine near Lake Louise, Alberta, Feb. 2023.
Rocky Mountain elk (Cervus canadensis) also follow a similar pattern, moving out of the high country and into the valleys in the fall, as snow accumulates in the mountains. A sure sign of the transition from late summer to autumn is the bugling of bull elk. By congregating in the valleys, elk are more likely to find open water for drinking and places where the lighter snow pack has blown off, melted, or sublimated (gone from solid snow to water vapour), revealing nourishing dry grasses and forbs to supplement browsing of shrubs. The ever watchful timber wolves (Canis lupus) mimic this migration, following their prey.
Rocky Mountain elk carcass in February 2022 along the Columbia River near Brisco, B.C.
From Jasper National Park north in the area of the Great Divide, the remaining endangered mountain caribou (Rangifer tarandus) still follows a unique movement pattern. Initially, as snow starts falling, individuals and small groups of mountain caribou move down into areas with less snow. Once the snowpack in the dense old subalpine forests has firmed up enough for them to stand on with their large snowshoe-like feet, they go back up into the high country. Here, they can now access arboreal lichens hanging from subalpine fir and Engelmann spruce, which sustain them until spring.
Sleep through it
The term for when animals “sleep” through the winter is called “hibernation”. The verb “to hibernate” comes from the Latin verb “hībernāre”, which means “to pass the winter.” Certain wild animals hibernate to survive the season of prolonged frigid temperatures and scarce food that typifies the months of November to March in the high altitudes and latitudes of Canada’s GDT. While hibernating, an animal’s body temperature, heart rate and breathing rate all drop to significantly lower levels (90% in the case of ground squirrels). These animals put themselves into a sort of suspended animation state for weeks at a time rather than try and survive tough weather conditions.
Hibernating animals can significantly lower their heart rate and body temperature when they “sleep”. For example, least chipmunks (Neotamias minimus) can reduce their heartbeat from 350 beats per minute to just four beats per minute during their periods of hibernation. True hibernators only fully wake every few weeks to eat small amounts of stored food and to pass waste. These animals dramatically drop their body temperature to below freezing, aided by their salty body fluids, which prevent tissue crystallization.
There are different degrees of hibernation with certain species employing a deep state of dormancy and others being easily aroused from a light torpid state. The main difference between hibernation and torpor is that during torpor, an animal is able to wake up easily if hurt or threatened by predators. Generally, smaller animals can more easily make the metabolic changes necessary for hibernation. Certain animal bodies are too big to get rid of the body heat required to hibernate.
Rapidly gaining weight and then lying still for several months is not generally considered a recipe for fitness, yet most hibernators that do this remain healthy during hibernation. Medical researchers study hibernation in the hopes of preventing osteoporosis and Type II diabetes, helping those suffering from kidney failure, and prolonging the viability of human organs for transplant. Other scientists are exploring how to put astronauts into “hibernation” for long space voyages.
Finding the Right Place to Sleep
Western toad at 1,890 metres asl in Waterton Lakes National Park, Alberta.
In October, as temperatures plummet, deciduous trees shed their leaves, and snow starts to fall in the high country near the Great Divide, Western toads (Anaxyrus boreas) seek hibernacula (sheltered places occupied in the winter by a dormant animal). Toads are cold-blooded, meaning their body temperatures take on the temperature of the environment around them. This puts them at great risk of freezing to death during a Rocky Mountain winter. A suitable spot for a toad to “hole-up” in for the winter could be a cozy small mammal burrow, a well-insulated niche in a beaver dam, or a rock chamber near a fast-moving stream that doesn’t freeze. The proximity of running water to stream-side hibernacula provides an environment that stays above 0 degrees C. Hibernacula in burrows or beaver dams must be sufficiently insulated and deep enough to stay below the frost line (up to 1.3 metres underground) to prevent the toads from freezing solid.
Overwintering in these terrestrial cavities minimizes the risk of predation. These sites also safeguard the toads from hypoxia (failure of oxygen to be utilized by body tissues), and anoxia (physiologically inadequate supply of oxygen), both likely fates for any amphibians trying to hibernate in the muck at the bottom of ponds where the pond freezes and also gets blanketed by snow. Toads must find hibernacula that are moist and yet do not freeze. In addition to providing protection against predators and maintaining adequate oxygen levels, a good toad hibernaculum must not get too dry or cold. Plus, it has to supply cues to trigger emergence from hibernation in March/April.
Once closeted away in their hibernaculum, Western toads lower their metabolism to the point where they use very little energy. Their heart rate and body temperature drops and they typically do not eat. Like other amphibians, Western toads breathe through their skin while hibernating, albeit at a slow rate.
Western toads in the Canadian Rocky Mountains can spend over half of their lives (six to seven years out of their ~13-year lifespan) hibernating. Unfortunately, scientists know very little about the wintertime behavior of Western toads or the microclimate of their hibernacula. Occasionally, people have seen Western toads basking in the sunshine outside their burrows on warm, sunny days during the winter months, suggesting that toads may be able to come out of and return back into a state of hibernation.
A Mourning Cloak is a large, long-lived butterfly that stays in the Rockies all year long.
Most butterflies in the Rockies either migrate south during winter or spend winter as a larvae. This is not the case for the mourning cloak (Nymphalis antiopa). This large long-lived butterfly (wingspan up to 9 cm) stays in the Rockies all winter long. These tough butterflies find a hole in a tree or crawl under some bark and rest all winter long in their adult form. They enter a state of dormancy similar to hibernation called “diapause” where they rest and remain very inactive.
In the spring, the overwintering adult mourning cloaks emerge. They may look a little tattered or ragged. But they have a head start over all those other butterfly species migrating back north or emerging as larvae or pupae.
As with many other native bees and wasps, once the first frosts begin, newly mated bumble bee queens locate a safe location for their diapause. Only the queen bee or wasp survives the winter, emerging from dormancy in spring.
Fattening up beforehand and reducing energy demands
Golden mantled ground squirrels try to fatten up before their winter hibernation.
From mid-August to September, golden-mantled ground squirrels (Spermophilus lateralis), the rodents most GDT hikers assume are chipmunks on steroids, gain extra weight and put on a special layer of fat. They also grow thicker fur coats. Golden-mantled ground squirrels usually make their dens near or under a tree or log. Typically, their dens aren’t dug very deep, but they can extend up to 30 metres. Unlike Columbian ground squirrels, they do not nest in colonies. Using its cheek pouches, each ground squirrel carries food to its individual den to eat in the spring when it wakes up.
As they begin hibernation in October, golden-mantled ground squirrels curl up in a ball to minimize their exposed surface area. Then these ground squirrels reduce their metabolism. They regulate their body temperature, maintaining it at ∼1°C above the ambient temperature in their dens. During hibernation, they suspend or substantially reduce many physiological and cellular functions, including respiration, reproduction, cardiac function, digestion, renal metabolism, mitosis, RNA translation, and immune function. Their metabolic rate can be less than six percent of non-hibernating values! This really conserves energy.
Golden-mantled ground squirrels, in common with all other mammalian hibernators, do not remain dormant or torpid continuously. They wake up repeatedly throughout the hibernation season (October to May) and temporarily achieve normal body temperature (∼37°C) at intervals of every two to ten days, only to reenter hibernation less than a day later. Biologists are still studying why this takes place. There must be negative physiological consequences to continuous hibernation and health benefits for periodic arousals. There is a cost to waking up, though. Up to 70% of a hibernating mammal’s winter energy expenditure occurs during these periods of wakefulness. The insulation provided by their fur helps conserve energy during hibernation by slowing body heat loss during the time when the ground squirrels are awake between torpor bouts. The increased density, thickness, and length of the hairs in their pelage significantly decrease thermal conductance in the winter.
Even though they wake up between torpor bouts, golden-mantled ground squirrels rarely consume the food they store in their den during the hibernation season. Instead, they survive the winter primarily by drawing fuel from their stored body fat. Studies show that nearly all of the decrease in body mass during hibernation reflects depletion of their stores of white adipose tissue. Their natural diet is high in linoleic acid, which reduces the melting point of their fat deposits, making them easier to metabolize at low temperatures. Feeding ground squirrels “people food” can interfere with this essential process, putting them at risk during their most vulnerable time of year.
When aroused from its dormant state in its den, a golden-mantled ground squirrel will spend most of its time moving about and rearranging nest materials. Occasionally, it will go to the surface and if possible, briefly leave its den. Although both sexes observe the same annual period of torpor, females have a significantly longer total hibernating period than males. Male golden-mantled ground squirrels experience longer bouts of continuous torpor, as well as longer periods of wakefulness.
Just like in Aesop’s fable, ants prepare for winter.
Golden-mantled ground squirrels are not the only alpine creature that employs this strategy of fattening up and then reducing its energy demands. In the autumn, most species of ants also devour large amounts of food to build up their fat stores. When cold air arrives, the ants’ body temperatures drop dramatically and they become sluggish. They seek out warm places, such as deep soil, under rocks, or under the bark of trees to reduce their energy demands. They close off the entrance to their nests as ant traffic slows down and ceases.
Inside their nests, ants cluster around one another to maintain body heat. Many huddle protectively around the queen, sheltering her as she carries the promise of the next generation. The extra fat the ants put on in the fall allows them to go without eating much throughout the long alpine winter. The ants enter a dormant stage, moving little. They absorb and metabolize the fats, carbohydrates and proteins they stored the previous fall. As warm weather returns each spring, ants emerge from dormancy, open the entrance to their nest, and head outside.
Although most species of mosquitoes die-off in late summer or fall when food becomes scarce and the temperatures drop, amazingly, even a few species go dormant in winter. They find holes under bark and elsewhere and huddle together for warmth until spring. In these species, only the females overwinter. They even “bulk up” and store fat, much like bears do before winter.
Sleep like a Bear — Lightly
For about three weeks in the fall, both grizzly (Ursus arctos) and black bears (Ursus americanus) enter a period of excessive eating called “hyperphagia”. It would be like humans at a Thanksgiving feast that lasted several weeks. During their fall feeding frenzy, each day, black bears can eat up to 20,000 calories and grizzlies as much as 30,000-50,000 calories and put on up to 1.4 kg of weight. Bears need to gain a lot of weight quickly since during hibernation they must survive entirely off their fat stores.
During the summer mating season, fertilized eggs will remain in a female bear’s womb but will not implant until weeks or months later. This helps Mama Bear to conserve energy until hibernation, and may be a way to control the population if food is scarce. If she has not accumulated enough fat by the time she settles into her den, the egg will spontaneously abort.
Bears sleep in dens that they excavate themselves, as well as in hollow trees or caves. They will use dens built by other bears. A bear can build a den in three to seven days. The timing of den building varies from bear to bear. While some bears make their dens months before hibernation season, others wait until the last minute.
Grizzly bears in the Rockies typically dig their dens on south or west-facing slopes at high elevation; black bears lower down toward the valleys. The den entrance is just large enough for a bear to squeeze through so it will cover quickly with insulating snow. The chamber is dug only slightly larger than the bear’s body to allow for maximum heat retention. On the few occasions where I have had the opportunity (in the summer!) to crawl inside an empty grizzly bear den, I have always felt amazed at how small it is.
Jenny at the entrance of a grizzly bear den In Mount Revelstoke National Park, B.C. in 1987.
After digging or finding a den, bears will line their winter bed with bedding material, usually consisting of grasses, leaves, and branches. This layer of bedding helps keep the bear warm during the cold winter. My husband Ian, our neighbour Laura, and I witnessed a black bear do exactly this in early December 2021 prior to denning in a ravine 300 metres from our houses near Invermere, B.C. The day after the bear backed into its den, pulling in the dry grasses all around him, snow fell and remained for the rest of the winter. The bear didn’t emerge until mid-March.
Black bear gathering and piling up dried grass to bring into its den (the hole above the culvert) in a ravine near Invermere, B.C., Dec. 3, 2021
We have all heard the expression “sleep like a bear”, meaning sleep deeply, or that bears “hibernate” through the winter. In fact, bears are awake and aware while in their dens even though they are in a reduced metabolic state. Their heart and breathing rates decrease and their body temperature goes down slightly. Bears do not eat or release bodily waste while in this torpor state. Bears can sleep more than 100 days without eating, drinking, or passing waste! Instead, through an amazing urea recycling process, bears are able to transform their pee into protein. The urea produced by their fat metabolism is broken down and the nitrogen is re-used by the bear to rebuild protein. Pregnant female bears wake up from torpor to give birth, then go back to sleep afterwards while nursing their tiny cubs. Bears are known to “wake up” during winter, leave the den, and explore their surroundings for food. After a day or two, however, they will return to the den.
Some species of wildlife go through a transformation in how they look in preparation for winter. The most well-known are the species whose appearance transitions from summer browns and greys to winter white to help them blend in with their changing environment. Other creatures completely change in other unique ways to prepare for winter.
Snowshoe hare beside cross-country ski trail in Peter Lougheed Provincial Park in March 2020.
Becoming Snow White
Seasonally moulting to white plumage, in the case of white-tailed ptarmigan (Lagopus leucura), or white pelage, as do snowshoe hare (Lepus americanus) and short-tailed weasel (Mustela erminae), happens for different reasons. Camouflage to conceal their whereabouts comes to mind immediately. When on snowy ground, white-tailed ptarmigan and snowshoe hares can hide more easily from predators in their winter white attire. The weasels do the same thing to make their appearance less obvious to the prey they hunt in winter and to evade larger predators like lynx or coyote that given the chance would devour them. However, another advantage of having a pale coat turns out to be that it has better insulating properties. White fur and feathers lack melanin, the substance responsible for colored hair and feathers. This leaves air spaces in the hair shafts and feathers. The air also scatters light, making these animals appear more bright white than other white mammals and birds.
This transition doesn’t happen overnight and so these creatures appear in a mottled state as autumn progresses into winter. With climate change affecting the timing of snowfalls and how long the snowpack persists, biologists observe with concern that these creatures are now more frequently white when their environment is not, making them more not less visible. For all of these species, the colour change is linked not to changing temperatures but to photoperiod, the amount of light received during a day. With shortening days, receptors in the retina transmit that information to the pituitary gland and central nervous system, stimulating the systematic moult of brown hairs or feathers and replacement with milk-white hairs or feathers in patterns peculiar to each species. Hormones and temperature can exert a secondary influence on the timing and quality of these moults.
Change Body Parts or Body Chemistry
Each fall, all species of grouse found in the Rockies grow tiny bristly projections called “pectinations” on the hard scales covering their feet. These comb-like protrusions nearly double each foot’s surface area, making it easier for the birds to navigate in snow. However, instead of the fleshy pectinations typical of other grouse, white-tailed ptarmigans produce expansive foot-feathers increasing both warmth and surface area and serving like insulated snowboots and snowshoes.
Since insects are cold-blooded animals, if they overwinter, their body temperature drops to that of the outside temperature, which can be below freezing. Yet the overwintering adult mourning cloak butterflies and other insects in diapause do not freeze because they can reduce the amount of water in their bodies, replacing it with glycerol, which is similar to the anti-freeze solution that people put in cars.
Certain bird species that one can see near the Great Divide, including the mountain chickadees (Poecile gambeli ), have an antifreezing adaptation known as a counter current heat exchange system. The arteries and the veins in the feet and legs run side by side, allowing cold returning blood in the veins to be warmed by the arteries. Abundant, dense feathers help conserve heat and keep exposed skin to a minimum.
In addition, chickadees possess the remarkable ability to go into regulated hypothermia each night. They can actually lower their body temperature, in a controlled manner, to about six to eight degrees C below their normal daytime temperature of 41.7 degrees C. This allows these tiny birds to conserve almost 25% of their hourly metabolic expenditure when it’s freezing outside. The lower the outside temperature, the more energy chickadees conserve.
Caribou (Rangifer tarandus) have the rare ability to change their eye colors. Like many other mammals and some other animals, caribou have a reflective layer behind the retina of the eye called the “tapetum lucidum”. This reflective layer allows their eyes to gather more light at night. The ability of this reflective layer to turn blue during long winters allows caribou eyes to become as much as 1000 times more sensitive to light.
Some insect species overwinter in a completely different shape, i.e., as larvae or pupae.
For several species of dragonflies (Odonata), their nymphs spend the winter underwater in water bodies that don’t freeze completely. In this active carnivorous stage, they continue to prey on other pond life. The larvae of horseflies (Family Tabandidae) go into a quiescent diapause period during winter, overwintering underwater or in moist soil. These larvae can still obtain air because of a respiratory siphon at their hind end.
Mountain pine beetle (Dendroctonus ponderosae) larvae thrive throughout the winter under the bark of pine trees, feeding on the phloem in channels constructed at right angles to their natal egg gallery. A prolonged period (four to five weeks) of cold temperatures (below -30 C for four or five consecutive weeks) will kill nearly all pine beetle larvae nestled inside tree trunks. This used to be the norm in the Great Divide area, but with the milder winters since the 1990s, more mountain pine beetle larvae survive. Summer hikers along the GDT witness the results, high numbers of dead lodgepole and other pine species.
Many of the alpine butterflies and certain moths overwinter as larvae and pupate in the early spring. Like other late-season caterpillars, the so-called woolly bear of the Isabella tiger moth (Pyrrharctia isabella) use natural materials to protect themselves from frigid temperatures. They find a protected place in late summer or autumn such as curled leaves, seed pods, crevices under rocks, or loose soil, and hunker down. Other butterfly larvae overwinter in groups, or in cocoons or silken nests. The larvae must be well camouflaged to avoid predation by birds and mice.
A banded woolly bear caterpillar near Akamina Pass in Waterton Lakes National Park in September 2023.
The ultimate shape shifters are swallowtail butterflies. In the fall, their caterpillars form a chrysalis and they overwinter in this pupal state. During this stage of life, the larval structures are broken down while the adult structures of the swallowtail butterfly form in the process called metamorphosis. Hover flies (family Syrphidae) which are important pollinators like the bees they mimic, also overwinter as pupae.
Western swallowtail butterflies overwinter in a chrysalis, emerging as adults in the spring
Prepare and Store or Cache Food
Several mammal species that live all year long in the Rocky Mountains capitalize on a temporary abundance of food in the summer by caching surpluses to eat in the winter. Storing food provides some insurance for survival given the uncertainty of finding adequate food during the upcoming lean times of snow and cold. American Pika (Ochotona princeps) and American red squirrels (Tamiasciurus hudsonicus) are among the mammals especially adept at preparing and storing food.
Periods of food scarcity also pose serious challenges for birds, especially when those times correspond with the cold temperatures typical of a Canadian Rocky Mountain winter. Caching ensures a reliable supply of resources to help offset these demanding circumstances. Birds in the Great Divide area that cache include mountain, boreal and black-capped chickadees (Poecile gambeli, P. hudsonicus, and P. atricapillus), red-breasted nuthatches (Sitta Canadensis), and all the corvids (Family Corvidae), which include nutcrackers, jays, crows, ravens and magpies.
American pika on Lineham Ridge in Waterton Lakes National Park (Photo by Ian Hatter)
The American pika has justly earned its nickname of “farmer of the mountains”. During the summer, a pika will chew off plant stems, collect a big mouthful of wildflowers and grasses, and then lay them out in little piles on sunny rocks or paths to dry. The sun drying technique ensures the plants don’t get moldy. As the plants dry and the pikas add more plants to the pile, they create a “haystack.” Pikas then move the dry haystacks into their dens deep among the rocks. Pikas are active throughout the entire year. They do not hibernate in winter, but tend to spend most of their time inside the den in the winter or travelling in tunnels under the snow and rocks. They rely on the insulating effect of ample snow to survive winter’s harsh temperatures. Pikas eat the grasses and other plants throughout the winter. They venture out to forage when the weather permits.
Pikas have an unusually warm resting body temperature of 40.6 °C and this enables them to tolerate the cold typical of Great Divide winters. Moreover, a pika’s metabolic rate is high and its thermal conductance is low. It thus generates a lot of heat internally and loses it gradually, helping it maintain a constant body temperature through the winter. In addition, pikas have other physical adaptations to help them survive cold temperatures. Their furry paws keep their toes warm and provide traction in the snow. Their thick coat of fur endows excellent insulation against the cold. Unlike the rabbits to which they are related, they have short and rounded ears to reduce the risk of frostbite.
American red squirrels start gathering food long before winter begins.
Like American pikas, American red squirrels stay active throughout the whole year. Squirrels start to prepare for winter long in advance as they do not hibernate. If you see a red squirrel frantically scurrying about in August or September, it’s getting ready for the upcoming cold months by gathering and storing food for future consumption. In a frenzy of activity in late summer and fall, red squirrels climb conifer trees, clip ripe unopened conifer cones, and then climb back down to retrieve them, carrying them to their storage area or “midden”. Wildlife researchers have documented that a hard-working squirrel can clip and store up to 12,000 ripe, unopened cones during this intense time.
The American red squirrel is omnivorous and enjoys a varied diet, including seeds, flowers, berries, fungi, insects, mice, eggs, and even small birds. In the vicinity of the Great Divide, their primary source of nutrition comes from the seeds in conifer cones, especially those of whitebark, limber and lodgepole pines, Engelmann and white spruce, Douglas-fir, and subalpine larch. They will cache and consume the seeds of sub-alpine fir but prefer the seeds of other species. Red squirrels also snip off and dry mushrooms, placing them carefully on a branch or on the ground where sunlight and air will hasten the drying process.
An American red squirrel stashed this mushroom in a young lodgepole pine protected by a large old subalpine larch
Red squirrels are experts when it comes to food storage. Using tree cavities, underbrush piles, or dens as their own pantries, these feisty, industrious rodents work hard to ensure that the food they’ve collected for the winter will be stored safely and kept away from cache-robbers. The key to their success are their food storage facilities or middens, large piles of conifer cones, and piles of scales from cones that have already been eaten by the squirrels, and leaf litter used to store food for winter.
A red squirrel develops its midden at the base of a good cone-bearing tree. The squirrel climbs the tree above the midden and runs out on a branch to sit. There, it holds a cone with its front feet and rapidly gnaws off the cone scales to reach the seeds inside. The scales pile up on the ground below, forming the midden. A large midden can be almost a metre deep and measure two metres wide or more. Most will be just up to a metre wide and half a metre deep. The accumulating pile of cone debris essentially forms a cold storage area for their food. Squirrels also round up new, unopened cones and bury them in the pile. The debris keeps the cones cool and locks in moisture. This keeps the stored cones from opening and losing their seeds. As long as they stay moist and cool, the cones can stay in this state indefinitely. As time goes on, the midden enlarges, as squirrels eat through more cones each year. A large midden may contain up to 15,000 cones. If you examine the midden, you may see tunnels. Squirrels use these to stash new-found cones and select the ones they want to eat. Depending on the size of the cone, squirrels can chew through 50-100 cones per day, eating the seeds stored inside. In a typical white spruce cone with two seeds per scale, there are approximately 130 seeds per cone, meaning a squirrel could consume between 6,500 and 13,000 spruce seeds in one day!
It took many generations of American red squirrels to build up this huge midden near Sunset Pass in Banff National Park, Alberta.
With their food supply centrally located, one can understand why squirrels are so protective of their territory and their midden. Red squirrels use their midden for years, fiercely defending it and their territory (an area around 1.6 hectares in size) from other squirrels. Young squirrels must either inherit middens from their mother or find and establish their own. The average life span for an adult red squirrel is two years, so there is turnover. Juvenile American red squirrels must acquire both a territory and a midden prior to their first winter. Otherwise, juveniles without a midden do not survive that first winter. If an adult squirrel dies, a juvenile seeking its own territory may “strike it rich” and find a midden with a full larder ready for the taking.
American red squirrels change their eating habits as winter appears imminent. They consume more food and try to fatten up. The extra layer of body fat that squirrels put on before winter insulates them, keeping their body heat inside and the cold out. This helps squirrels lower the need for foraging and endure the food scarcities of winter, allowing them to spend more time in the comparative warmth of their dens, further reducing their energy needs. Red squirrels tend to be very physically active. They dart, scurry, and leap. Their constant movements generate body heat and keep them warm. If feeling cold, squirrels shiver. The vibrations generate body heat. Nevertheless, despite their cold repellent nature, red squirrels can succumb to frostbite and hypothermia in extreme weather.
Clark’s nutcracker, Peter Lougheed Provincial Park, Alberta, March 2016.
While American red squirrels put all their seeds in one big midden, corvids such as the Clark’s nutcracker (Nucifraga columbiana) and Canada jay (Perisoreus canadensis) employ “caching”. This food storage technique involves gathering and concealing food items in small batches that they retrieve later. A “cache” refers to hidden food. Typically small in size, these edibles can be secreted away under leaf litter or logs, in nooks high up in trees, behind tree bark, and in holes pecked in the topsoil.
Starting in the summer, the nutcrackers fly from tree to tree, using their beaks to pry open pine cones (primarily whitebark and limber and also ponderosa and lodgepole) and collect seeds. These birds can amass 32 seeds per minute, tucking them into special storage pouches under their tongues. Each Clark’s nutcracker can pack about 100 seeds in their mouths. They then need to carry them to where they create their small caches (one to 14 seeds per cache). Nutcrackers make their caches between two and 33 km from the source tree and often at a different elevation. Each Clark’s nutcracker makes 5,000 to 20,000 separate seed caches throughout its home territory annually. As it quickly creates its caches, usually in less than 30 seconds, it consigns the location and contents of each individual cache to a map in its brain. A nutcracker can cache up to 98,000 seeds during the summer and fall. They store more than they actually need as insurance against loss due to seed pilfering and the lack of alternate foods such as insects, berries, and eggs in the winter months.
At high altitudes, Clark’s nutcrackers depend on cached seeds as their major source of food throughout the winter and well into the spring breeding and offspring rearing season. They use their spatial memory to locate their concealed caches. Studies of caching show that their memory for cache sites may last as long as seven to nine months, and that nutcrackers find 80% of their caches. This likely underestimates their prowess, since nutcrackers sometimes return to a cache site only to find that pilferers such as unrelated nutcrackers, other jays, squirrels or other rodents have robbed some sites. It indicates amazing powers of recall. These birds return to accurately recover their stashed seeds many months after caching them. They retrieve the seeds despite the significant environmental changes that take place between the time of caching and salvage. For example, nutcrackers make caches in summer when green plants and flowers blanket the landscape and retrieve the seeds after this vegetation has died and disintegrated. Nutcrackers also make caches in the autumn before snow arrives and yet later dig down through a metre of snow to recover them.
Clark’s nutcrackers employ diverse methods to find their numerous seed caches. They memorize two or three permanent landmarks or objects in the vicinity of their caches, which they use to later triangulate the cache’s location based on the cache’s proximity to the landmarks. The birds may also note landmarks, but rather than relying on distances, they use angles to find their cache. They also use trial and error. Snow burying landmarks certainly makes it more challenging. Sometimes a nutcracker will perch on a low-lying branch to survey an area before swooping down and digging through the snow only to have to go back to its branch to consider things again before trying another nearby spot.
Nevertheless, each year, some stored seeds never get reclaimed, either because the bird who cached them gets killed, circumstances change enough that the bird cannot find the cache, or the bird cannot remember a particular cache. Many of the hiding spots nutcrackers favour prove ideal for seed germination. So, a forgotten cluster of seeds can sprout into seedlings.
Nutcrackers bear significant energetic cost for long-distance seed transport and caching, particularly in regions as tough as the Great Divide. To offset this, nutcrackers seek out the seeds of the endangered whitebark pine. These seeds are as calorie dense as is chocolate and more fat-laden than butter, making them ideal winter sustenance. Clark’s nutcrackers are thus the primary means of whitebark pine seed dispersal and are essential for the recovery of this tree species at risk.
Caching allows Clark’s nutcrackers to breed in January and nest in February, giving them a head-start on the birds that migrate south for the winter. The Clark’s Nutcracker is one of very few corvids where the male incubates the eggs. The male nutcracker develops a brood patch on its chest just like the female, and takes his turn keeping the eggs warm while the female goes off to get seeds out of the caches she made.
Canada jay, Peter Lougheed Provincial Park, Alberta, March 2020.
Unlike Clark’s nutcrackers, Canada jays do not eat conifer seeds. However, these scatter-hoarding birds cache in conifers. Studies show that Canada jays can rapidly identify conifer species and then preferentially exploit those conifers as cache locations. These jays make quick, fine- scale habitat assessments. They discriminate among trees of different species and employ what they see in terms of the shape and structure of the tree to choose the perfect cache-sites. When few potential high-quality conifer cache sites exist, jays will actually cluster their caches in whatever conifers are present, rather than put them in what they perceive as unfavorable locations such as deciduous trees. Canada jays select conifers since conifer resin has protective properties that aid in cache preservation by preventing food spoilage. This is important because, unlike most scatter-hoarders, Canada jays cache primarily perishable food. Without protective measures, their highly perishable cached items would decay over time. Research in 2011 and 2015 indicates that Canada jay breeding success, abundance, and distribution is closely associated with the availability of high-quality habitat, specifically a high density of spruce, because these conifers best preserve the contents of Canada jay caches.
Canada jays enjoy a varied diet that changes seasonally, including insects, spiders, berries, seeds, mushrooms, eggs, small rodents, pieces of scavenged meat, as well as anything they can persuade human visitors to part with. From June until autumn, these jays make many thousands of little home-made energy balls, making up to 1000 caches daily. They carefully chew their food morsels and coat the resulting mixture in lavish amounts of their sticky saliva, which is believed to possess antibacterial qualities. Then they tuck their sustainable spit ball snacks in crevices in conifer branches, among conifer needles and tree lichens, and under the bark of conifer trees. They favour the cool, very shaded branchy areas in spruces, the intersections of branches and twigs, and where a branch emerges from a trunk. Super-sized salivary glands that stretch from the corner of a Canada jay’s bill and almost meet inside the back of its head, supply the super-glue that keeps the “boluses” (the technical term for the gooey food blobs) intact and firmly stuck to where they’re cached. Unlike other corvids, these jays do not need heavy bills to hammer or chop hard frozen food in the winter. They can easily use their blunt little bill to detach a bolus and thaw it out in their mouths.
Possessing remarkable visual memories, Canada jays can find thousands of their hidden tidbits months later. They remember various details about their caches, including location, contents, and even the relative time when the cache was made. They can actively evaluate and process information about cache sites prior to caching, in addition to retaining information about caches that have already been made. Studies indicate that their memories enable them to recall nearly every single hiding spot within a one-square-kilometre territory. This is daunting news for anyone who has ever forgotten the whereabouts of one’s iPhone, car, or house keys.
Like the nutcrackers, the jays cache food to combat resource scarcity. Both species are so good at storing sufficient food that they breed in January and nest in February/March. This precedes the end of the alpine winter and is long before the breeding and nesting season of most other perching birds. Both nutcrackers and jays use their cached food to feed their offspring. So, in both species, both adult and offspring survival depends on food caching.
Male Canada jays choose the nursery site and initiate nest-building in early February. Each male jay assembles twigs and binds them into a loose ball using caterpillar cocoon thread. Then his mate pitches in, adding a ring of sticks to the top of the ball and filling in the gaps with bits of lichen and bark. Together, the pair use feathers and fur scavenged from elk or deer carcasses along with their saliva to line their creation. By squeezing their bodies inside, the parents form what they have made into a cup-shaped nest about five cm deep. Only the female jay incubates the eggs while the male provides her with food from his caches. After the hatchlings have sufficient feather cover to stay warm without their mom, both parents spend the rest of February and the month of March feeding their young even during blizzards. The jays can feed their nestlings entirely from the boluses they’ve stored away. By the time the migrating birds return in April/May, the Canada jays’ offspring have already fledged, giving them a head start on foraging. Unlike most other birds that nest in spring and summer, Canada Jays spend that time caching food for the next winter.
Depending on the risks they perceive, Canada jays flexibly employ a few different non-mutually exclusive cache-protection strategies including cache depression, out-of-sight caching, and spacing. These context-specific strategies reduce the risk of cache theft and increase the likelihood that their caches will stay available for their own use. By placing caches high in conifers they reduce the risk of losing food to mice and other ground-dwelling rodents. Nevertheless, every year Canada jays lose some of their caches to unrelated jays, other corvids, and American red squirrels.
Stashing their caches up high in conifer trees instead of burying them in the ground like Clark’s nutcrackers, means that Canada jays will flourish in areas that continue to receive a heavy snowpack, i.e., deeper than a metre. However, their reliance on caching mostly perishable food items may render their caches more susceptible to climate-change-induced deterioration, particularly as alpine winters experience more freeze-thaw periods and alpine spring, summer and autumn temperatures rise. Some argue that this is already happening. The long-term results from the Alberta Breeding Bird Survey in data books from 1971 to 2015 show that Alberta’s Canada jay population has decreased by 35%. Fortunately, Canada jays demonstrate great adaptability. When they encounter novel situations such as exceptionally early, warm spring weather, they direct foraging efforts away from their less nutritious, less palatable defrosted and refrozen “freezer-burned” caches to the emerging higher quality fresh foods.
Certain wildlife species seem to just tough it out, enduring the fierce alpine winters in the vicinity of the Great Divide, some teetering on the edge of survival and others flourishing despite their harsh habitat. Among these are the mountain goat (Oreamnos americanus), the lynx (Lynx canadensis), and the common raven (Corvus corax).
Mountain goat in on Mount Wardle Kootenay National Park with its characteristic long thick coat.
Mountain goats feature the thickest and longest pelage of any North American ungulate except for muskox. With their bearded chins and the long hair of their upper legs resembling pantaloons, they look distinctive. To prepare for severe alpine winters, mountain goats grow thick two-layered coats. Their winter coat consists of coarse hollow guard hairs up to 20 cm long and very fine, interwoven underfur that is five to eight cm long. This allows goats to withstand brutal temperatures and the most severe wind chill.
While in summer, mountain goats will range up to 15 km across their home mountain, in the wintertime, snow conditions often force a goat herd to stay on a ridge less than one km in length with a total area of eight to ten hectares. They select high areas with steep cliffs where the snow sheds readily or windswept ridges where little snow accumulates. Mountain goats prefer that the ridge faces the sun to the south or southwest for warmth. This exposure also helps keep the ridge clear of snow. Having short legs means mountain goats easily become “high-centered”, floundering when trying to travel through deep, soft snow. So, a mountain goat herd remains in this restricted winter habitat from mid-October until April, roughly half the calendar year. Ideal winter habitat for mountain goats is a sunny, south-facing, steep-sided windswept mountain “island” surrounded by a sea of deep, soft snow.
In these habitats, mountain goats find exposed vegetation not eaten during the summer as well as shrubs and lichens, enough to survive. As long as the snow is no more than half a metre deep, they can use their hooves to remove it and access the dry grasses and other alpine plants underneath. If the snow gets compacted, it takes more energy for a goat to paw it away, or it may even become impossible to do so. Kids born the previous spring may be too small to paw away snow and depend on their mothers to do this for them. Even then, kids have a 50:50 chance of survival in their first year largely due to starvation and exposure during the winter. If they can hang on until spring, alpine plants on south-facing slopes start new growth sooner than on slopes facing north and east.
Unlike most creatures, in winter, mountain goats no longer need access to running water as they can eat snow instead to supply their hydration requirements. Since the quantity and quality of forage is low, mountain goats also burn body fat accumulated in summer and fall. They depend on body fat reserves accumulated the rest of the year to survive the brutal cold and winds. Goats sleep a lot in winter to lower their caloric needs. They also restrict their movements. Still, they can lose up to 27% of their body weight over the winter. Moving in winter is costly as it consumes vital energy from fat reserves. Starvation may occur in late winter and early spring when fat reserves are depleted, particularly if new plant growth is delayed by a lingering deep snowpack and/or spring snowsqualls.
Although treacherous, the rugged south-facing windswept ridges not only provide some sustenance for the goats, but they provide protection from predators. This is especially true if a ring of deep, soft powder snow encircles their mountain in the subalpine timberline zone that separates the forested valley from the high windswept ridges in the alpine. The snow must be soft enough to inhibit large predators from travelling from the lower valleys to the sub-alpine and alpine winter range of mountain goats. If the snow remains soft and deep, the predators cannot penetrate the ring of snow.
However, sun, rain, and wind can change soft powder snow into a crusty or rock-hard surface that can support a predator’s weight. People also create trails through soft powder snow when they ski, snowshoe, or snowmobile through an area. These trails harden within an hour and can then support the weight of many predators. Any human-made trails that go from a mountain valley to the alpine facilitate predators reaching mountain goats at their most vulnerable time of year. When predators or human visitors disturb mountain goats in the winter, the exertion needed to escape may rob them of vital fat reserves. Fleeing could also expose the goats to avalanche hazards or force them into a new place with less nutritious and/or inadequate amounts of feed. From this standpoint, it’s a good thing if people do not use the GDT in winter, at least in the places where it overlaps mountain goat winter range.
The characteristic “ice cream cone” shape indicates lynx tracks in deep snow.
Lynx live in coniferous forests, where the snow gets very deep in winter. They have long, soft coats with extra-long hair on their legs and paws to keep them warm. Compared to their body size, they have huge, hairy paws that act like snowshoes. Just as snowshoes keep people from sinking in the snow, lynx paws can support twice as much weight on packed snow. Lynx can spread their fur-covered toes apart making the surface area even larger. This, along with their long legs, allows these cats to wade through soft, deep snow with ease and use their larger back legs to help power big leaps either up trees or when bounding to catch up to its preferred food, the snowshoe hare.
In one of the longest, most well-studied examples of a predator-prey interaction, lynx were found to prey almost exclusively on snowshoe hares during the winter months. Hares comprise 75-90% of a lynx’s diet on average. In the summer and when hare populations are low, lynx switch to consuming other small animals like American red squirrels, mice, and ptarmigan. However, lynx prefer hares. Hares are particularly nutrient-rich. They thus imbue lynx with the necessary energy and fat reserves needed to survive long, cold winters.
The number of hares in an area determines the number of lynx that can survive there. Snowshoe hare populations are cyclic: they peak about every ten years then crash shortly thereafter. Lynx follow this pattern, lagging about one to two years behind the hares. When hare populations boom, lynx have better survival rates and females can support more kittens to adulthood. Extensive studies show that an abundance of food and high reproduction rates will increase lynx population density to 30-45 lynx/100 km2, but once the hare numbers drop, lynx population density plummets to just two lynx/100 km2.
Common raven at Bow Lake in Banff National Park at -37 degrees C, December 2011.
Over the years, I have often seen common ravens (Corvus corax) nonchalantly hanging out near the Great Divide despite deep snowpacks, the most bone-numbing temperatures and bitter cold winds. They appear to endure and even thrive in winter. How do they do it?
A key advantage is their large size, as it gives them a slower rate of heat loss than other perching birds. They have high metabolisms that generate a lot of heat, like a very efficient furnace. They also sport specialized feathers on their nostrils to retain moisture. Their strong massive beak can be used like a hatchet to break apart frozen food.
Ravens are incredibly intelligent, communicative, curious, and opportunistic. They are flexible about what they eat and how they acquire it. Ravens can and will kill almost any small animal that they can catch. However, they figured out long ago that given the high energy demands required to survive mountain winters, meant they would need to feed on the carcasses of large animals they could never kill. So, ravens learned to exploit carnivores such as wolves. Amazingly, ravens have been documented to arrive at and feed on wolf kills within minutes after a pack kills an ungulate, such as an elk. Some human hunters have observed the same phenomenon after they shoot a moose or deer. They will also cache any surplus food.
Ravens profit from each other’s experiences. They share information. A single raven might catch sight of a carcass of a bighorn sheep killed in an avalanche. It tends to return to the nocturnal roost, and let its companions know. Soon a crowd of ravens follows the discoverer to the feast. For most of the winter, ravens share food as a crowd. However, there are times when the first fortunate raven to discover a carcass does not willingly share information with its fellow ravens. During the breeding season in February, a territorial pair of ravens will fiercely defend a carcass from others.
The American dipper (Cinclus mexicanus) is another astounding bird that endures sub-zero temperatures. Even in the dead of winter, one can see these aquatic songbirds near or in clear, cold, rushing mountain streams with rocky substrates and that flow through forests. To survive swimming in or under cold waters during the winter, dippers have a low metabolic rate and extra oxygen-carrying capacity in their blood. They wear a thick coat of waterproof feathers, thanks to an oil gland above their tail. They also have handy nostril flaps that keep water out and extra eyelids, called nictitating membranes, to help see under water. In winter, they consume mostly aquatic insect larvae, including those of mayflies, mosquitoes, and midges, as well as very small fish, fish eggs, snails and some worms.
Some species of wolf spiders (Family Lycosidae), particularly the alpine wolf spider (Melocosa fumosa), endure mountain winters by living in miniature underground burrows and excavations made by other small creatures and sheltering in rock crannies under talus and scree. From here, they make nocturnal hunting forays under the snow in the sub-niveum, preying on small insects that can be stalked even in the winter months. The tapetum lucidum in the back of each of their eight reflective eyes gives them incredible night vision.
At least three other species of arthropods can be observed living out their lives above the snow in the vicinity of the Great Divide, including springtails, snow scorpionflies, and wingless snow-walking craneflies (see “Snows of the Great Divide” in the February 21, 2022 issue of the Pathfinder Newsletter).
Count on the Next Generation
In the Aesop’s Fable, “The Grasshopper and the Ants”, a hungry grasshopper, who sang and danced its way through the summer and fall, begs for food from the ants when winter comes. The ants, which have worked hard since spring to store food in anticipation of the lack of nourishment and cold temperatures of winter, refuse. The tale was meant to provide moral lessons about the virtues of hard work and planning for the future.
Two two-striped grasshoppers (Melanoplus bivittatus) preparing for winter in Waterton Lakes National Park, Alberta.
Adult grasshoppers, like many insects, do spend their summer living life in the moment and then perish with the first hard frosts, whereas, as mentioned earlier, ants store food and persist. However, grasshoppers as a species continue because they mate and lay eggs long before winter begins. Although the adults die, the next generation overwinters as specially adapted coated eggs buried deep undergound. Many species of insects use this strategy, overwintering as eggs, from certain types of mosquitoes to aphids. Even some dragonfly species lay eggs that survive the winter and hatch into nymphs the next spring or summer.
Although this adult dragonfly perished when winter arrived, the next generation will emerge next spring.
Many alpine butterfly species adopt this same practice of counting on the next generation. The eggs of the Rocky Mountain Parnassian (Parnassius smintheus) must survive the frigid temperatures of the long alpine winters and not get fooled to hatch before they should if warm Chinooks blow or the jet stream moves north allowing warm southerly air to shift up into western Canada. If a resumption of the chill of winter doesn’t kill prematurely hatched larvae, the food plant where their egg was laid will. From November to February, the leaves of the lanceleaf stonecrop become fatally toxic to these larvae even though from March to October the same plant supplies the nutrition that this butterfly’s caterpillars depend on. The eggs must be very cryptic to avoid detection and consumption by predators like spiders, rodents and birds.
Although the adults of the Rocky Mountain Parnassian die each fall as temperatures plummet, their eggs survive and their caterpillars hatch next spring to feed on lanceleaf stonecrop.
All of these examples illustrate that how wildlife prepares for winter near the Great Divide varies greatly from leaving, sleeping, changing, caching, enduring, or counting on the next generation. Being the biggest and strongest doesn’t guarantee survival. Over millennia, successful wild creatures have had to master the equation of energy output versus input, bearing in mind all of the factors and ensuring they (or their next generation) have enough calories to persist into the future. Perhaps there’s a moral lesson here for a new Aesop’s fable.