with six pups born per pack and more than half of pack members
lost to mortality and dispersal each year (Mech 1970; Cochrane 2000). A
dispersing wolf may pair with one of the opposite sex and colonize a
vacant territory or may join another pack and replace a missing breeding
member (Mech 1970; Rothman and Mech 1979). A wolf population can
cover thousands of square kilometers with several independent but interacting packs. In the western Great Lakes region (Minnesota, Wisconsin,
and Michigan), midwinter pack territories average 150 to 180 km
2 (Fuller
et al. 1992). Range expansion is facilitated by great variation in dispersal behavior: some wolves establish territories and mate near their
natal territories, whereas others move long distances (Gese and Mech
1991).
Although gray wolves once lived throughout the Lake States, European
settlers nearly eliminated wolves through intensive, unregulated exploitation. By 1960, wolves were limited to the wilderness of northeastern
Minnesota, contiguous to a large Canadian wolf population, and Isle
Royale in Lake Superior (Mech 1970). Following protection under the U.S.
Endangered Species Act in 1973, wolf numbers and range in the Great
Lakes region increased. Yet in the core wilderness range within the Superior National Forest, Minnesota, precipitous local extirpation of whitetailed deer (Odocoileus virginianus) caused a sharp decline in wolf numbers
in the 1970s until the remaining wolves switched to hunting less numerous
moose (Alces alces) (Mech 1986). The wolf decline was thought to be
spreading westward into Voyageurs National Park in the mid-1980s (Gogan
et al. 2000). Thus, while wolves were generally faring well by the 1980s, their
long-term persistence was still not certain throughout the western Great
Lakes region.
After determining that most wolf mortality near Voyageurs Park was
caused by humans, either accidentally or by deliberate illegal killing, biologists raised concerns about recreational disturbance impacts on the park’s
wolves. Interagency consultation with the U.S. Fish and Wildlife Service on
park development proposals in 1992 led to stipulations for a cumulative
effects model to assess the long-term fate of wolves in the park (Cochrane
2000). At the same time, wolves had moved into the largely forested region
of northern Wisconsin, but their fate was uncertain because they had
colonized isolated areas with relatively low road densities within a humandominated landscape. To meet recovery goals in Wisconsin and Michigan’s
Upper Peninsula, wolves would have to be able to survive in nonwilderness
conditions. Modeling was seen as a useful approach to explore wolf viability in human-dominated landscapes (Haight et al. 1998).
By the late 1990s, the picture for wolves was much more favorable, with
their range covering most of northern Minnesota, northern Wisconsin,
and upper Michigan (Figure 2.1). In 2000, the population in Minnesota
exceeded 2400 wolves (W.E. Berg and S. Benson, Minnesota Department
of Natural Resources, personal communication, 2000), and the populations
2. Modeling for Endangered-Species Recovery
25
lost to mortality and dispersal each year (Mech 1970; Cochrane 2000). A
dispersing wolf may pair with one of the opposite sex and colonize a
vacant territory or may join another pack and replace a missing breeding
member (Mech 1970; Rothman and Mech 1979). A wolf population can
cover thousands of square kilometers with several independent but interacting packs. In the western Great Lakes region (Minnesota, Wisconsin,
and Michigan), midwinter pack territories average 150 to 180 km
2 (Fuller
et al. 1992). Range expansion is facilitated by great variation in dispersal behavior: some wolves establish territories and mate near their
natal territories, whereas others move long distances (Gese and Mech
1991).
Although gray wolves once lived throughout the Lake States, European
settlers nearly eliminated wolves through intensive, unregulated exploitation. By 1960, wolves were limited to the wilderness of northeastern
Minnesota, contiguous to a large Canadian wolf population, and Isle
Royale in Lake Superior (Mech 1970). Following protection under the U.S.
Endangered Species Act in 1973, wolf numbers and range in the Great
Lakes region increased. Yet in the core wilderness range within the Superior National Forest, Minnesota, precipitous local extirpation of whitetailed deer (Odocoileus virginianus) caused a sharp decline in wolf numbers
in the 1970s until the remaining wolves switched to hunting less numerous
moose (Alces alces) (Mech 1986). The wolf decline was thought to be
spreading westward into Voyageurs National Park in the mid-1980s (Gogan
et al. 2000). Thus, while wolves were generally faring well by the 1980s, their
long-term persistence was still not certain throughout the western Great
Lakes region.
After determining that most wolf mortality near Voyageurs Park was
caused by humans, either accidentally or by deliberate illegal killing, biologists raised concerns about recreational disturbance impacts on the park’s
wolves. Interagency consultation with the U.S. Fish and Wildlife Service on
park development proposals in 1992 led to stipulations for a cumulative
effects model to assess the long-term fate of wolves in the park (Cochrane
2000). At the same time, wolves had moved into the largely forested region
of northern Wisconsin, but their fate was uncertain because they had
colonized isolated areas with relatively low road densities within a humandominated landscape. To meet recovery goals in Wisconsin and Michigan’s
Upper Peninsula, wolves would have to be able to survive in nonwilderness
conditions. Modeling was seen as a useful approach to explore wolf viability in human-dominated landscapes (Haight et al. 1998).
By the late 1990s, the picture for wolves was much more favorable, with
their range covering most of northern Minnesota, northern Wisconsin,
and upper Michigan (Figure 2.1). In 2000, the population in Minnesota
exceeded 2400 wolves (W.E. Berg and S. Benson, Minnesota Department
of Natural Resources, personal communication, 2000), and the populations
2. Modeling for Endangered-Species Recovery
25