Winter Predation: A New Frontier for the
Voyageurs Wolf Project
By Tom Gable
Project Lead
Voyageurs Wolf Project
Last winter, we embarked on a new area of research for the Voyageurs Wolf Project—studying the predation behavior of wolves during winter in the Greater Voyageurs Ecosystem (GVE). In particular, we sought to understand and quantify how frequently wolves kill deer in winter and how that varies with pack size, winter conditions, and deer density.
For much of the past decade, we have almost exclusively studied the summer ecology of wolves. And by summer, I mean the biological part of the year when wolves rear pups, which starts in early April when wolves give birth to pups and continues until late October when pups are mature enough to travel nomadically with adult pack members.
Looking out over an abandoned rendezvous site in a grassy beaver meadow during the summer of 2019.
We focused on this period because little was known about many aspects of wolf ecology during summer in southern boreal systems like the GVE. Wolves are quite difficult to study during summer in forested ecosystems where observing them on a regular basis is impossible. Fortunately, when we started the project in 2015, recent technological innovations, namely GPS-collars and trail cameras, made it possible to study the ‘secret lives’ of wolves in ways that had not been successfully done before in the Northwoods.
We have learned much about the summer ecology of wolves over the past decade because of these technological advances and many miles in the woods (often in pretty miserable conditions!). For instance, we have uncovered previously unknown behaviors such as wolves hunting fish, ambushing beavers, and foraging on berries and have described previously unknown phenomena such as how wolves impact wetland creation and alter the composition and trajectory of forests.
Yet, for many years, we have wanted to gain a better understanding of wolf predation during winter, and how predation changes with winter conditions. This feeling was only reinforced when we dug into the scientific literature and realized there was surprisingly little research on kill rates of wolves on white-tailed deer during winter.
However, despite our interest, we simply have not had the financial and logistical capacity for much of our project’s duration to add a large winter field season to our plate. Recently, that has changed.
​
The subadult male from the Listening Point pack traveling along a game trail in the winter of 2023.
Indeed, thanks to the generous support of thousands of private donors, funding sources such as the Minnesota Environment and Natural Resources Trust Fund, non-profits, and foundations, our project finally reached a point, financially and logistically, where we were able to add a winter predation component to our research in Winter 2023-2024.
And it was a fortuitous time to do so because Winter 2023-2024 turned out to be the mildest winter on record in the GVE and much of northern Minnesota. This meant we were able to study what wolf predation on deer was like at one extreme of winter conditions in Northern Minnesota, a helpful data point to compare to other winters moving forward.
A video of a wolf chasing a deer during the end of 2023. The winter of 2023-2024 was the mildest winter on record, and there was not much snow accumulation as you can see in this video. Captured by one of our trail cameras.
During February and March 2024, we tracked two packs in the GVE to identify every kill they made during this period to understand how frequently these packs were killing deer and how much food these packs were acquiring each day of the winter.
Deer are more vulnerable to predation in winter because snow makes it more difficult for deer to move and evade wolves, and there is not high-quality, herbaceous forage for deer to replenish energy reserves. The increased vulnerability of deer means wolves are usually able to kill deer more often during winter than other times of the year. As a result, winter is typically when wolves put on body weight and build up critical fat reserves for the upcoming summer, which is a lean season for wolves.
But this was not the case during the historically-mild winter of 2023-2024. Instead, we learned wolves struggled to kill enough deer to meet their daily caloric demands, and as a result, wolves lost body weight during the winter. Most deer, it seems, were not vulnerable to predation, likely due to the lack of snow cover for most of the winter.
Replace
Pictures of wolves from the winter of 2023-2024. Notice the malnourished appearance on all individuals. Interestingly enough, a few packs suffered from a dog louse outbreak, contributing to an even more sickly appearance.
This winter work also revealed that wolves did not kill enough deer during Winter 2023-2024 to have a negative impact on the deer population. Rather, at a minimum, the deer population remained stable during the winter, and more than likely increased. For example, deer hunting success, which closely follows changes in deer populations in the GVE, increased by 14% this past fall, strongly suggesting the deer population increased.
The big takeaway from our first year of winter predation work is that winter conditions seem to be the primary driver of wolf predation on deer populations. If winters are mild, predation on deer is low; if winters are severe, predation on deer will likely be considerably higher. Thus, increases or decreases in deer populations appear largely driven by winter conditions—not wolves—in northern Minnesota and other similar ecosystems. The magnitude of wolf predation is simply a symptom of winter conditions.
We published the results of this research in a peer-reviewed journal in late 2024 so other biologists and researchers could learn from our results. If you want to read this study, which we think is a fairly-accessible read (not too science-y), check out this link where you can download a PDF of it!
A pack of five wolves traveling across a frozen lake.
In January, we started our second year studying wolf predation in winter. This winter, though mild, is already more ‘wintry’ than last year and we have about 16-18” of snow blanketing the forest right now. We are currently studying the predation behavior of 5 packs in various portions of the GVE, which should allow us to understand how predation levels this winter compare to last year.
In particular, we are curious about whether the predation levels we observed during the historically mild winter are an anomaly or if they are typical of predation levels during most mild winters. Data from this winter, if it continues to be mild, should be telling!
Importantly, we want to thank you for your support! Your generosity made this research possible and has facilitated the overall success of our project in ways we could not have imagined when we started this work a decade ago.