The boom-and-bust cycles of lynx and snowshoe hares are well known. Lynx numbers are driven by hare numbers and hare numbers are driven by food availability. Across the boreal forest, snowshoe hare populations follow a predictable cycle, peaking every 8 to 10 years before sharply declining. Lynx populations mirror this boom-and-bust pattern because lynx are closely tied to snowshoe hares in a predator-prey relationship.
Canada lynx in the snow
Historical Data and Population Cycles
Students will analyze population data from a “real world” predator-prey system. Students will compare data from this real world system with the simple predator-prey model they investigated in the previous activities. The Hudson Bay Company in Canada bought pelts from trappers during the 1800s and early 1900s.
For 90 years, from 1845 to 1935, the Hudson Bay Company kept detailed records of the number of lynx and hare pelts they acquired from trappers each year. These counts of pelts provide an approximate measure of the lynx and hare population sizes during the 90-year period. The lynx and hare predator-prey relationship is a good real-world example of the simple predator-prey system modeled earlier in this lesson.
Figure 7 shows a graph of 90 years of data from the Hudson Bay Company. The graph shows the number (in thousands) of hare and lynx pelts acquired by the Hudson Bay Company. Discuss that the pelt count is not a direct record of the hare and lynx populations.
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Both the hare population and lynx population rise and fall in cycles, as was the case in the model. The graph of historical data isn’t as smooth as the graph of model data, which is generally the case. The peaks and valleys of population levels for both species vary substantially in shape and maximum values. In several cases (especially around 1865, 1915 and 1925) the lynx population clearly peaked slightly after the peak of the hare population.
The data represents the number of pelts turned in to the Hudson Bay Company, not the actual population of that creature in the wild. Other factors besides the actual population would have influenced the number of animals captured and pelts turned in i.e. the relative value of lynx versus hare pelts, the relative ease of capturing each creature, and so on. It seems likely that the population of hares in the wild must have been much greater than the number of pelts turned in. In general, there are significantly more individual prey organisms than individual predators in most ecosystems.
The strength of models is typically not in predicting an exact population value at a specific future time, however, the shape and pattern of the model-based graph was similar to the historical data. Models, therefore, can be helpful when making predictions about overall patterns or trends.
Lynx and the Hare Population Activity
Factors Affecting Hare Populations
Local Arctic residents noticed that in some locations there was a different boom cycle. Peaks were higher and lasted longer than in other locations. The difference? Mineral licks. When hares had access to mineral-rich soil, they were able to maintain higher population numbers for longer.
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In 1997, biological technician Donna DiFolco and her team began tracking snowshoe hare numbers in and around Gates of the Arctic National Park and Preserve in hopes of untangling how changes in hare populations may be affecting lynx in the region. When Donna and her team began monitoring snowshoe hares in 1997, they counted hare tracks along a 2-mile (3.5-km) transect.
Snowshoe hare tracks
Just a year later, in 1998, the team ran into trouble because there were so many tracks that it was difficult to accurately count them. As Donna recalls, “I felt I was unable to get a good count due to all the overlapping of tracks and the packed snow. From 1998 to 2001, measurements of plant browse (the leaves, shoots, and stems hares eat) clearly showed the toll the booming hare population was taking on the local vegetation. Spruce seedlings were stripped of their bark, needles, and branches by hungry hares, and many died. Willows in the area were also heavily browsed.
While talking with Jack, who lives in the village of Wiseman just east of the park, Donna learned something surprising about snowshoe hares. Jack shared that he had observed hares visiting mineral licks-areas of bare soil rich in minerals. Jack, along with other Wiseman residents, had also noticed that hare populations in some areas would reach an extremely high peak-a “super-peak”-about once every 20 years, with a much smaller peak occurring in between.
This sparked Donna’s curiosity, so in 2007, she and her team expanded their study to include pellet counts. Pellets-small, round droppings left behind by hares-are a reliable index of hare population densities. This gave the team another way to determine the number of hares when they entered the “boom” phase of their life cycle and their tracks were hard to count. A mineral lick-the soft light-gray substrate-in the central Brooks Range (left). Hare pellets accumulate on dried leaves during a time of high snowshoe hare populations (middle). A volunteer checks a plot for snowshoe hare pellets during an annual survey (right).
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From track counts conducted between 1997 and 2023, Donna and her team confirmed that snowshoe hare populations followed a distinct boom-and-bust cycle. In 1998, they recorded a super-peak of over 200 tracks per 100 m, the highest observed during the entire study. But by 2003, the population had crashed, with track counts dropping near zero. A small peak was observed in 2009, only to be followed by another dramatic crash. In 2019, a second super-peak occurred, reaching about half of the 1998 peak.
During super-peak periods, the team observed that overcrowding forced some hares out of areas with dense willow cover that provided both food for browsing and protection from predators. When that happened, hares were more likely to be hunted by lynx and other predators (such as great-horned owls). This helped explain the hare population crashes observed in the region.
Donna’s team compared pellet counts at mineral sites and non-mineral sites. In non-mineral areas, the hare population peaked around 2017-2018. However, in mineral areas, the population continued to increase until it peaked in 2019.
In 2015, the team had set up cameras at sites in both mineral and non-mineral areas. At first, the cameras only captured typical hare behaviors-feeding, grooming, and resting. But by 2017, some cameras began to capture hares visiting mineral licks and engaging in geophagy (eating or licking the soil). When Donna and her team analyzed pellets collected at mineral licks, they found their ash content was significantly higher-about 17%-compared to pellets from other sites where ash content ranged from 2 to 12%.
Since it began in 1997, this study, along with other research it has sparked, has deepened our understanding of snowshoe hare ecology. While Donna retired from the National Park Service in November 2024, her colleagues will continue to monitor snowshoe hares in the Gates of the Arctic region, aiming to discover more about super-peak cycles and determine how, when, and where mineral licks influence hare populations.
Lynx Adaptations and Hunting Behavior
With long legs, and huge, snowshoe-like paws, Canada lynx have evolved to hunt in the deep snows of a mountain winter. Canada lynx are among the rarest wildlife species to spot. They’re highly adapted to winter conditions, making them expert hunters in deep, persistent snow.
Unlike grizzly bears, Canada lynx require highly specific habitat. They seek slopes with thick vegetation cover to build their dens and shelter their kittens. They also hunt in these areas with horizontal cover-meaning lots of plants, rocks and fallen trees close to the ground-since that’s where their prey will hide. Additionally, these areas must retain the snowy winter conditions lynx require to gain a competitive advantage while hunting.
Lynx rely on snowshoe hare as their main source of prey, with the single species comprising up to 96 percent of their diet. When hare populations are high, lynx can eat up to one hare per day. Because of this relationship, the two critters have evolved together, with hare developing winter adaptions to avoid lynx, and lynx in turn developing winter adaptions to catch them.
Much of what’s known about lynx diet and hunting behavior has come from scat analysis and snow tracking. Studd used snow tracking to verify hunting data obtained from an accelerometer and audio recorder. Biologging offers a new way of looking at hunting behavior, particularly of small prey.
Impact of Climate Change
Climate change has led to warmer winters across Canada lynx and snowshoe hare habitat. This often means less snow, which both species rely on, as well as faster and more frequent melting of snow. Recent research and observations also show that snowshoe hare change their coat color based on the photoperiod, or length of day, and not the presence of snow.
Hares can now be spotted more frequently with a white coat before snow has come down in the fall, or when the snow has already melted in the spring, making them easy targets for predators.
The snowshow hare is common in Canada and the United States. It is brown in the summer, but molts to a white coat in the winter. When motionless in the snow, it is impossible to detect. Males are slightly smaller than females. This hare breeds at one year of age and can have as many as four litters in a season when food is plentiful. Population density exhibits extreme fluctuations, and can range from 1 to 10,000 per square mile across the species range.
With shorter winters due to climate change, there can be a mismatch between the timing of snow cover and molt; that means you can get white hares on a mostly brown landscape in early spring and late fall. Taken together, the different impacts of a couple of extra snow-free weeks on either side of winter could change the amplitude of the predator-prey cycle, Boutin says.
The Role of Predation and Other Factors
Although the cyclical relationship between hare and lynx has long been documented, exactly what makes the hare population collapse is not well understood, with “ecologists divided into two camps: those that believe that the little things run the world and it’s a bottom-up process… and those that believe it’s a top-down process where predators regulate the food web.”
“That’s what (biologists) have been trying to untangle for the last few years now - is it bottom-up or top-down? There’s evidence for both, in reality. It’s not as simple as just one choice,” Jung notes.
“What seems to be driving hare populations in some cases is an increase in their predators.” Meat-eaters such as great horned owls, golden eagles, wolverines and coyotes are capable of “prey switching” and “tune into snowshoe hare” when they are plentiful, putting increased pressure on the population as it rises, he says.
Lynx Behavior During Hare Population Crashes
Across large swaths of Alaska, Yukon and the Northwest Territories, snowshoe hare (Lepus americanus) populations have crashed, causing extreme hardship for the Canada lynx (Lynx canadensis), which relies almost exclusively on the hare for sustenance. When hare populations across areas of Alaska, Yukon and the Northwest Territories have crashed, hungry lynx “need to get creative”, says Jung.
Lynx, which grow to around a metre long and weigh around 10 kilograms, are far too small to tackle larger prey species such as moose and caribou, and may turn to livestock and pets for food. This year’s crash has led to a rash of attacks, including two separate incidents in Yellowknife and Beaver Creek, YT, where women had to physically overpower the large cats to save their dogs from being dinner. A man in Anchorage, Alaska, recently chased off a lynx displaying predatory behaviour towards his two-year-old daughter in their backyard.
“They’re not usually long distance travellers, like wolves… which move at a trot and can cover 50 km a day that way,” says Kielland. “These guys (lynx) are moving at a walk. It’s very puzzling.”
Although some lynx do certainly perish during lean times, changes in lynx population during these periods is not solely related to mortality; when the going gets tough, lynx may simply get going, moving hundreds of kilometres from their home ranges in search of prey, says Knut Kielland, a professor of ecology with the University of Alaska who studies lynx.
A recent study of 150 collared lynx headed by Kielland found the animals “took off in all kinds of directions” as food supplies dwindled, with some collared animals moving as far south as British Columbia and Alberta.
Conservation Efforts and Future Research
What Canada lynx and snowshoe hare need now more than ever is connected habitat. In response to the challenges from the changing climate both species may explore new areas, seeking habitat at higher elevations, on colder sheltered slopes, or farther north. Open, wild corridors make that movement possible.
If fire suppression is to continue, forestry methods need to change by doing a better job of mimicking natural disturbance processes (especially fire), that are specific to each region. Likewise, global warming is adding a new challenge for both lynx and hare by changing the nature of wildfires.
Ivan says he’d love to sit down with the Forest Service, silviculturists, recreation managers and land managers, and ask them if there are techniques available “to protect these really important areas from wildfire. Can you do that? Or is that … off the table?
While Donna retired from the National Park Service in November 2024, her colleagues will continue to monitor snowshoe hares in the Gates of the Arctic region, aiming to discover more about super-peak cycles and determine how, when, and where mineral licks influence hare populations.
Table: Snowshoe Hare and Lynx Population Dynamics
| Species | Population Cycle | Primary Diet | Habitat |
|---|---|---|---|
| Snowshoe Hare | 8-10 year boom-and-bust cycle | Vegetation, bark of young trees | Boreal forests, areas with dense willow cover |
| Canada Lynx | Mirrors snowshoe hare cycle | Snowshoe hare (up to 96% of diet) | Slopes with thick vegetation cover, areas with snowy winter conditions |