Wolf Population Expansion in Minnesota
By William Berg and Todd Fuller, Minnesota Department of Natural Resources
Wolves were bountied in Minnesota from 1849, when they were worth $3, through 1965 (when all bounties ended in Minnesota), when a bountied wolf pelt brought $35. Although bounties generally did not control populations of other predators, they had an impact on wolves. By the early 1900s, wolves were rare in southern and western Minnesota. By the 1950s, wolves were gone from these areas of the state.
A wolf study conducted by Milt Stenlund in the early 1950s centered on a portion of the Superior National Forest in northeastern Minnesota. After extrapolation to the rest of northern Minnesota, Stenlund’s data indicated a population of 450-700 wolves, most of which resided in 12,000 square miles of main wolf range.
Through the early 1960s, wolf numbers were likely stable (see Minnesota Wolf Population Trend graph below). From 1953 to 1965, about 190 wolves were bountied annually, and bounty claims gradually decreased outside the main range — suggesting that fewer wolves existed. One estimate in 1963 put Minnesota’s wolf population at 350-700. After the bounty ended in 1965, wolves could still be legally trapped and hunted year-round in Minnesota. Minnesota Department of Natural Resources (MN DNR) records indicate that about 250 wolves were killed annually until 1974, when wolves became completely protected under the federal Endangered Species Act of 1973.
In the mid-1970s, biologist L. David Mech extrapolated the wolf densities from three study areas in Minnesota to the known wolf range at that time and estimated a population of 1,000-1,200. During the winter of 1978-1979 field personnel from several resource management agencies were queried by the MN DNR. Their knowledge, combined with results from four radio-tracking studies, resulted in a state-wide population estimate of 1,235 wolves. This figure persisted as the official population estimate for ten years. In the early 1980s work by Mech, Steve Fritts and Bill Paul identified areas of newly colonized wolf range that suggested range and population were expanding to the west and south.
In winter 1988-1989, the methodology of the MN DNR’s 1978-1979 survey was repeated, using an even larger sample of natural resource agencies and personnel, as well as incorporating geographic computer technology. As a check, a second method used the well-established relationship between densities of wolves and ungulates — in Minnesota’s case, deer and moose, to estimate wolf numbers. Both methods estimated the wolf population at between 1,500 and 1,750. There were at least 233 wolf packs, with the average pack size being five. This survey identified about 23,000 square miles of existing and potential wolf range.
The DNR wolf survey was repeated in the winter of 1997-98, using an even larger base of natural resource professionals and applying more advanced GIS technology. That survey estimated a population of 2,450 wolves residing in a contiguous pack range of about 34,000 square miles. A total of 385 packs existed in the contiguous range, in addition to several west and south of the “new wolf range.
The successful recolonization of vacant wolf habitat over a span of three decades resulted from high deer densities, wolves dispersing from existing packs, and wolves colonizing new areas. This has been documented in all wolf telemetry studies done in Minnesota. All colonization of new areas has been done by the wolves themselves, unlike some states where wolves have been reintroduced by natural resource agencies. While some wolves dispersed to new areas from the major wolf range identified in 1978, others dispersed from the very few scattered packs in north central Minnesota that survived the bounty era. An example is one pack that the MN DNR had ear-tagged or radio-collared from 1969 to 1980, which occupied a 100-square-mile area southeast of Hill City. Besides being partly responsible for the eventual startup of five neighboring packs, the Hill City pack sent dispersers to Boy River, Walker, Hinckley and Baudette, distances ranging from about 28 to 135 miles.
Populations of white-tailed deer, the main prey of wolves in Minnesota, benefited from many mild winters and accelerated timber harvests over the years. These factors, which reduce winter-caused mortality and create more suitable habitat, allowed the deer herd to increase most years, even in the main wolf range. In Minnesota, each wolf takes the equivalent of 18 to 20 adult sized deer per year on average. Based on this average, wolves kill the equivalent of about 40,000 deer per year, compared to deer hunters, who have taken 60,000-80,000 deer across the entire wolf range through the 1995 deer season. But then, winters got much worse. The 1995-96 and 1996-97 winters set records for their severity, and deer numbers decreased by about half. Consequently, deer hunters took about 25,000 deer (all bucks) in 1996 in the Minnesota wolf range, while wolves, whose numbers remained unchanged, continued to take about 40,000 deer.
When prey populations fluctuate dramatically, predator numbers usually follow, and wolf numbers stabilized (if not slightly decreased) following the deer decline, albeit temporarily. The winters of 1997-98 through 1999-2000 were among the mildest on record, thereby allowing the deer and the wolf population to again increase. By 1999, the deer hunter harvest had increased to 73,000 deer, and the wolf scent station index (DNR’s annual index of the wolf population) rose to a new record for Minnesota.
How many more wolves can Minnesota hold? And how should wolves be managed? Wolf populations increased about 6% annually in the 1970s, about 3% annually in the 1980s. All indications are that those increases have continued during the 1990s, and about 4.5% currently. Annual increases of this magnitude can be equated to compounding bank interest in a savings account, and doubling your money (or wolf populations) every 15 to 20 years. Wolf range, as well, continues to increase. Much of the unoccupied and potential range identified in the 1988-1989 survey, and even many areas deemed unsuitable for wolves, now contain wolf singles, pairs or packs. Some wolves are surviving in areas with higher road densities (more than one mile of road per square mile of area) and human densities (more than ten people per square mile) than identified as critical to wolf survival in 1988-1989. Wolf packs have even colonized Camp Ripley in Morrison County. Dispersal continues to areas as distant as the west-central and south-eastern part of the state, the northern Minneapolis/St. Paul outer suburbs, as well as North and South Dakota. Thus, wolves seem to be adapting more to humans and, perhaps due to more education about wolves, humans are becoming more accepting of the wolf’s presence. The most wolves that the MN DNR believes Minnesota can sustain without increased wolf-human conflicts is about 2000.
The 1992 Eastern Timber Wolf Recovery Plan established a population goal for Minnesota of 1,251 to 1,400 wolves by the year 2000. By the early 1980s, Minnesota had already reached that goal and by the late-1990s had nearly doubled that number. With the recovery of the wolf populations in Minnesota, Wisconsin and Michigan, the U.S. Fish and Wildlife Service may soon reclassify the wolf in these populations