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Do Wolves Affect White-Tailed Buck Harvest
In Northeastern Minnesota?

Introduction


Wolf numbers in Minnesota, Wisconsin, and Michigan have exceeded the criteria for recovery and removal from the federal list of endangered species in those states (Michigan Department of Natural Resources 1997, Wisconsin Department of Natural Resources 1998, Berg and Benson 1999). After delisting, each state will regain management responsibility with temporary federal oversight. One biological and political issue important to the design of a sound wolf management plan is the question to what extent wolves affect deer hunting, for deer are the primary prey of wolves in all 3 states. Minnesota alone hosts some 400,000 deer hunters (Fuller 1990).

Many aspects of wolf-deer interactions have been studied (Stenlund 1955; Pimlot et al. 1969; Mech and Frenzel 1971; Kolenosky 1972; Potvin et al. 1988; Mech et al. 1991). However, the resulting information is only partly relevant to the question of wolf effects on deer hunting. The latter subject has had little scientific attention. In the Superior National Forest (SNF) of northeastern Minnesota, Stenlund (1955) concluded that wolves reduced deer browsing pressure, and thus in some ways, benefitted the herd while at other times wolves competed with hunters. In part of this region where deer habitat was poorest, wolves and severe winters extirpated the wintering deer herd during 1968-1974 and reduced deer numbers in the surrounding area (Mech and Karns 1977). This area included 3,000 km² of wilderness largely inaccessible during the hunting season. Because deer declined throughout northern Minnesota, the Minnesota Department of Natural Resources closed the deer hunting season for 1971 and implemented more restrictive antlerless deer hunting regulations in 1972 and 1973, and restricted the take to bucks only since 1974 (Mech and Karns 1977).

A few attempts have been made to numerically examine the interactions among wolves, deer, and hunters. For the area described above, a simple model using wolf and deer numbers predicted the deer demise (Mech and Karns 1977). A more complex model, utilizing data on hunter harvest and winter severity, indicated for the region around the void, that "without wolf predation the deer herd would have declined very little by 1976 but that with the known wolf densities the deer population would drop to less than 0.4 deer/km²" (Mech and Karns 1977:21). The actual density dropped to 0.3-0.7 deer/km² (Nelson and Mech 1986a), with wolves killing 20% of the legal bucks in the area and hunters taking 30% (Nelson and Mech 1986b).

For an area 130 km west of ours, Fuller (1989) modified a model by Keith (1983) to examine interactions among wolves, human hunters, and deer and showed graphically the minimal hypothetical effect of wolves on human harvesting of deer. The most direct study of wolf competition with human hunting was conducted in Quebec where wolf numbers were experimentally reduced by 40-71%; the authors concluded that "the harvest of bucks was not affected" (Potvin et al. 1992:1595).

These studies yielded certain insights into the effects of wolf predation on deer harvesting by humans. However, they also had limitations. The deer decline on SNF in the early 1970's was extreme, and the exact role of poor habitat and several severe winters was unknown. The Keith-Fuller models were hypothetical and based on assumptions that might not be valid. For example, wolf predation and hunting mortality were considered completely additive to other mortality factors. Furthermore, in Fuller's (1989,1990) study area, only 10% of the deer mortality was due to wolves, whereas some 77% was due to humans, so wolf predation was relatively light. In the Quebec wolf-removal experiment, wolves had repopulated the removal areas within 8 months, greatly confounding that study (Potvin et al. 1992).

Thus, additional information is needed on the question of wolf competition with human harvests of deer. One approach to the subject is to examine data on wolf numbers and deer harvests in an area where wolves and humans have both killed deer over a long enough period to include a good representation of weather conditions and their effects on deer numbers. We use such data from the central SNF of northeastern Minnesota from 1975 to 1997 to test the extent to which wolves might influence deer hunting there.


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