Last updated: March 27, 2025
Article
Why Snowshoe Hares Use Mineral Licks
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. But 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. This opens up new ways to look at the many other species that use mineral licks and how they can supplement their diets in times of scarcity.
Snowshoe Hare Visits Mineral Lick
Video Player is loading.
Visit our keyboard shortcuts docs for details
- Duration:
- 10.133 seconds
A snowshoe hare visiting a mineral lick near Gates of the Arctic National Park and Preserve. A recent report, "Snowshoe Hare Population Trends at Mineral and Non-mineral Sites in the Central Brooks Range, Alaska" by Donna DiFolco and Julie Maier, corroborated local knowledge of hares using mineral licks during “super-peaks” when their populations explode to very high numbers. NPS
Snowshoe Hare Population Cycles – A 25-Year Journey
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. When hare numbers surge, lynx populations rise with them, and when hare numbers crash, lynx numbers fall soon after.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. Over the next 25 years, their study grew in unexpected ways to make use of new methods and pursue questions that were raised when local experts shared their observations of hare behavior with Donna and her team.
NPS / Donna DiFolco
Early Insights – The Impacts of Booming Hare Numbers
When Donna and her team began monitoring snowshoe hares in 1997, they counted hare tracks along a 2-mile (3.5-km) transect. At the time, the hare population was booming and starting to peak—but this peak was far larger than usual. 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. I started measuring browse…to supplement the track data to better show the impact hares were having on the area.”
NPS / Donna DiFolco
Geophagy – The Hares’ Hidden Diet
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. According to Donna, “[Jack] wondered if mineral consumption (geophagy) by hares might adversely affect lynx, because he noticed that lynx became skinny and showed a change in the color of their flesh (it got darker) when hares were eating mineral [soil].”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. In other areas, hare populations would peak at about the same level, about every 10 years. Jack believed these patterns in hare population cycles could be linked to the location of mineral licks, since “mineral areas” where populations reached super-peaks were found to the north of Wiseman, while “non-mineral areas” were located to the south.
Hare Geophagy - Snowshoe Hare Ecology Project
Video Player is loading.
Visit our keyboard shortcuts docs for details
- Duration:
- 4 minutes, 45 seconds
Learn more about the study – and hear from Jack Reakoff – in this video. NPS
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. But the pellets offered an additional benefit; they could be collected and tested for their ash content, indicating the hare’s use of mineral licks.
NPS / Donna DiFolco
Super-Peaks – Hares in Overdrive
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. These fluctuations followed the predicted pattern: a rapid increase in numbers followed by a sharp decline.
NPS / Donna DiFolco
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. But what sustained the very high numbers of hares during super-peaks?
The Mineral Advantage – How Geophagy Supports Super-Peaks
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. This confirmed the observations of local trappers and knowledge holders, including those Jack had shared with Donna: Hare populations in areas with mineral licks reached larger peaks that lasted longer.
NPS / Donna DiFolco
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). Between 2017 and 2020, the licks were visited almost 3,000 times, with most visits taking place in 2018 and 2019, when hare numbers were climbing toward a second super-peak.
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%. This result confirmed another observation reported by local residents: Hares were indeed consuming minerals from the licks during population super-peaks. Mineral licks were acting as a critical source of nutrients— sodium, calcium, potassium, and magnesium—that helped hares stay healthy when their usual food (plant browse) was in unusually high demand.
Hare Geophagy Nolan Flats
Video Player is loading.
Visit our keyboard shortcuts docs for details
- Duration:
- 10 seconds
Trail cameras capture snowshoe hares visiting mineral licks near Gates of the Arctic in winter. NPS
Two Hares Scratching
Video Player is loading.
Visit our keyboard shortcuts docs for details
- Duration:
- 9.567 seconds
Trail cameras capture two snowshoe hares visiting a mineral lick near Gates of the Arctic in summer. NPS
A Look to the Future
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. Beyond hares, this study also provides valuable new methods that can be used to study how other mammals might use mineral licks to supplement their diets, particularly when food resources become scarce in the harsh environments of arctic Alaska.Even though I’m bowing out, I’m really glad that the project is not going to stop and that my colleagues…are keen to keep it going. There’s still more that can be learned and the continuation of the project should eventually either confirm or reject the hypothesis that mineral licks somehow influence snowshoe hare populations enough that there are predictable differences in their population cycles at a smaller scale [and] local level.