Wolf population in the Greater Voyageurs Ecosystem increases in 2021-2022

By Tom Gable

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Wolf pups of the Cranberry Bay Pack in Fall 2022. 

           Every year, we use remote cameras and GPS-collar data to study and understand the wolf population of the Greater Voyageurs Ecosystem (GVE), Minnesota. Much of this effort is focused on determining the number of wolves in each pack and the size of pack territories in order to estimate wolf population density in the GVE. Wolf density is a reflection of wolf population size and is typically measured as the number of wolves per 1000 square kilometers (km).

 

A low-density wolf population would generally be around 1-10 wolves/1000 square km, a moderate density would be somewhere around 20-30 wolves/1000 square km, and a high density population would be >40-50 wolves/1000 square km. Annual density estimates allow us to understand how wolf population size in the GVE changes through time, and our hope is that, with enough time and data, we might get insight into the factors (e.g., prey density, disease) that influence wolf population change.

Figure 7. The known and estimated home ranges of 16 wolf packs in the Greater Voyageurs Ecosystem, Minnesota from April 2021 to April 2022. Colored polygons represent known wolf pack home ranges (n=9) based on GPS-collar data from April 2021 to April 2022. Notably, there are two home range polygons for both the Tamarack and Cranberry Bay Pack because we had two wolves collared in each pack (a home range polygon for each wolf in the pack).White polygons represent pack home ranges (n=7) that we estimated using a combination of remote camera data, historical home range data, and data on neighboring wolf pack home ranges.

The territories of 16 wolf packs in the Greater Voyageurs Ecosystem, Minnesota from April 2021 to April 2022. See our 2021-2022 report for more details.

Current wolf population estimates

We recently completed our 2021-2022 Wolf Pack and Population Size report and are excited to share the report with everyone (download report here). The big takeaways from this year’s report: wolf population density in the GVE during 2021-2022 was 63.2 wolves/1000 square km, which is an increase of 16% from 2020-2021 and 48% increase from the recent population low in 2019-2020.

 

The increase in population density appears to be the result of a dramatic increase in pup survival. In 2020-2021, we estimated that a mere 7% of wolf pups survived to adulthood. In contrast, our preliminary estimates for this past year indicate 52% of wolf pups survived.

 

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Wolf pups of the Half-Moon Pack in a den in Spring 2021.

The increase in pup survival is evident in the size of wolf packs in Winter 2021-2022.  Indeed, average pack size was 4.7 wolves per pack this past winter compared to 3.1 wolves per pack in Winter 2020-2021. 

 

For perspective, the wolf population in 2021-2022 was very similar to average wolf population density during 2014-2022 (61.5 wolves/1000 square km). Although annual population density has fluctuated during this period, there is no indication that the population has increased or decreased during this period. Instead, the wolf population in the GVE has remained at very high densities for almost the past decade. 

Current and historical wolf population estimates

One objective of this year’s report was to also examine and discuss how current wolf population density in the GVE compares to historical estimates of wolf population density. Prior to our research, there had been 2 major studies of the wolves of the GVE: the first was from 1987 to 1991 and the second from 1998-2001.

 

Both of these earlier studies estimated wolf population density was substantially lower than it has been over the past 9 years. During 1987-1991 and 1998-2001, wolf density was estimated to be 46% (33.5 wolves/1000 square km) and 37% (38.6 wolves/1000 square km) lower, respectively, than during 2014-2022. 

After a careful review of the data and methods used in earlier studies, we concluded that earlier studies almost certainly underestimated wolf population density. Moreover, we think it is highly likely that current wolf population density is similar to wolf population density during 1987 to 1991 and 1998 to 2001.

 

For anyone interested in why we think this, check out our recent population report where we provide a detailed explanation and analysis of how we arrived at this conclusion. But, the main takeaway from this assessment is that the GVE has likely sustained a dense, relatively stable wolf population for at least 35 years!

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Wolf density in the Greater Voyageurs Ecosystem, Minnesota from 1985 to 2022. Data from 1987-1991 and 1998-2001 are from two previous studies of wolves in and around Voyageurs National Park. 

Why use wolf density to measure population size?

After reading all of this information about wolf population density, you might be wondering why we use density to measure wolf population size instead of the total number of wolves in the Greater Voyageurs Ecosystem. We get asked this question frequently and the answer is two-fold.

 

First, the Greater Voyageurs Ecosystem—like most areas where wolves are studied—does not have distinct boundaries that delineate the population. For example, many wolf pack territories straddle the boundary of the GVE and lone wolves rarely remain in the GVE for the entire year, choosing instead to wander far and wide. Therefore, it is particularly tricky, and a fool’s errand from our perspective, to even try to determine what wolves are “in” or “outside” of the GVE population. 

 

Fortunately, estimating population density resolves these challenges because density is a measure of the number of wolves per area and is not affected by whether wolves straddle the border of the GVE, how many lone wolves are in the GVE at any given time, etc.

 

In other words, we do not need to count all the wolves in the GVE to get a good estimate of population density. Instead, we can study a subset of wolf packs in the GVE to estimate several wolf population metrics like average pack and territory size. We can then use these population metrics to calculate wolf density. Our goal, of course, is to study as many packs as possible to ensure our estimates are as robust and accurate as possible.   

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The Shoepack Lake Pack crossing a frozen beaver pond in Winter 2019-2020. The two wolves leading the pack are the breeding pair, which continued to lead the pack in Winter 2021-2022.

The second reason we use density to measure the population is because density estimates allow us, and other scientists who read our work, to compare the GVE wolf population with other populations across North America, Europe, and Asia. Putting the GVE wolf population in context would be challenging if we measured the population by the number of wolves in the GVE.

 

For instance, we could conclude there are 80 wolves in the GVE but what if we wanted to know if the wolf population in the GVE was larger than Yellowstone National Park? The best way to assess this would be comparing the number of wolves per area (i.e., wolf density) in both the GVE and Yellowstone. In other words, wolf density is a universal population metric that allows scientists from dramatically different areas to compare wolf population size. 

Going forward

Our long-term goal is to keep the Voyageurs Wolf Project running for decades. With enough years of data, we hope to gain a better understanding of why the wolf population in the GVE experiences annual fluctuations but remains relatively stable over time.

 

Regardless, one thing is for certain: annual wolf population data like that described above will be valuable for understanding virtually every aspect of wolf ecology that we are currently exploring and we are excited to see what we will learn in the years ahead!

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Members of the Nashata Pack pausing on a frozen beaver dam in Winter 2021-2022.