It’s an important question to answer, as it carries a lot of weight when it comes to managing wolves
2,856 wolves! That was the latest Minnesota Department of Natural Resources estimate of Minnesota’s wolf population in winter 2016-2017. That important number drives a significant amount of discussion related to the management of gray wolves in Minnesota.
How is that estimate made? It carries with it a lot of weight: Population goals were set to mark wolf recovery, and the success or failure of that recovery is measured by those estimates. Thus it’s important to understand what is behind it.
“Knowledge of these annual population numbers is vital to effective wildlife management, but gaining that knowledge is not easy,” said Rob Schultz, executive director of the International Wolf Center. “Free-roaming wolves are rarely seen, are more active at night, live in very wild places, roam widely and exist in low densities.”
All wolf counts are made during winter when the populations are close to their lowest in the annual cycle after reproducing in spring and sustaining mortality throughout the year.
Direct counts of wolves are difficult; they’re attempted when the area of census is small, as in the case of Isle Royale National Park in Lake Superior, 210 square miles. In Minnesota’s 27,570 square-mile wolf range, DNR and collaborators study packs in numerous study areas, and then use that data to extrapolate findings to the wolf population across the entire range.
“Methods used to count wolves vary depending on funding, difficulty of terrain and weather conditions,” Schultz said. “Winter snow-track surveys, monitoring radio-collared wolves or a combination of these methods are standard. Citizen reports, carcass retrievals, trail cameras and other techniques are also used across the U.S. wolf range.”
Managing wild animals is generally the business of individual states. Where wolves have been listed as federally endangered or threatened, the U.S. government conducts their population reviews using data collected by the various states. While the state-specific methods are variable, qualitatively many rely on the same approach.
So how are the estimates made? Here’s what happens in Minnesota: Formerly, the DNR estimated its wolf population about every 10 years. Since 2012, the DNR has counted wolves every year. Biologist John Erb explains the present approach. “I view the estimate like determining the outer boundary of a puzzle; how many puzzle pieces (pack territories) are in the puzzle, and how many wolves are on each puzzle piece.”
According to a report prepared by Erb, Carolin Humpal and Barry Sampson of the DNR’s Forest Wildlife Populations and Research Group, the method used to estimate the population uses three key pieces of information.
First, the DNR estimates the total area of land occupied by wolf packs. This estimate is based on information and observations from scores of conservation officers, foresters, biologists, technicians and other field workers throughout the state. This provides an estimate of “occupied range”, or how big the ‘puzzle boundary’ is in MN.
Second, they estimate the average wolf-pack-territory size, yielding an estimate of how many pieces (packs) can fit in the puzzle.
Third, they determine mid-winter pack size, or how many wolves there are, on average, on each puzzle piece.
Because it would be impossible to radio-collar all wolf packs within the state, DNR relies on data collected from a sample of packs around the state, a collaborative effort between DNR and Federal, Tribal, and University entities. Typically about 30 to 50 wolf packs are monitored during all or part of the survey period. Average pack-territory size and mid-winter pack size were estimated from data on many of those packs.
Wolf pack range
The overall wolf range within Minnesota hasn’t changed significantly since 1997-78 the DNR concluded.
“It is likely that occupied range changes on a comparatively slow timescale compared to fluctuations in average territory and pack size,” the report reads. Hence, while DNR is estimating population size annually now, wolf range (‘how big the puzzle is’) is re-assessed only at five-year intervals. The range will be re-evaluated this winter, Erb said.
The DNR estimates (2012/13 survey) that the wolf range in Minnesota is 70,579 square kilometers (27,570 square miles) and assumes little change in recent years. However, wolf range is now being re-evaluated based on data being collected this winter.
Pack territory size
The DNR concluded that the average territory size for a wolf pack in Minnesota during 2016-17 was 139 square kilometers (54 square miles). That average is smaller than last year but not “significantly different from most estimates obtained after 1998” the DNR says.
Mid-winter pack size
To determine the average mid-winter pack size, “radio-marked wolves were repeatedly located via aircraft during winter to obtain visual counts of pack size,” the report reads. “In cases where visual observations were insufficient, we also rely on any estimates of pack size based on tracks observed in the snow and trail camera images from within the pack’s territory.”
The DNR concluded in the most recent survey that the mid-winter pack size for 2016-17 was 4.8 wolves. That number has varied little since 1988, ranging from 4.3 (2014) to 5.6 (1989).
Running the numbers
With those three estimates in hand, the DNR estimated that there were 508 wolf packs in Minnesota during winter 2016-17. When they multiplied 508 by 4.8 (the average pack size), they came to 2,438 ‘pack wolves.’
In addition, it is assumed that the overall population contains an additional 15 percent lone wolves temporarily unaffiliated with any pack. When those figures were added up and all the various calculations were tabulated, the DNR came to its estimate of 2,856 wolves, or four wolves per 100 square miles of occupied range.
The margin of error in the studies is typically in the range of +/- 500 wolves. That means that if the estimate formulated by the DNR comes out to 2,850, the count could range from between 2,350 and 3,350, a difference of 1,000 wolves.
“The Minnesota DNR annual wolf counts represent some of the most accurate and reliable in the country,” said Dave Mech, a USGS senior research scientist who has studied wolves for 60 years.
The International Wolf Center aims to educate the public about wolves. It publishes International Wolf magazine, offers outreach programs to schools and operates an interpretive center in Ely with a pack of resident gray wolves. For more information on the Center, visit wolf.org.
Portions of this release were taken from an article written for International Wolf magazine by Dick Thiel and Diane Boyd.