The Wild World of Wolves
Assessing Potential Gray Wolf Restoration in the Northeastern United States
David J. Mladenoff & Theodore A. Sickley
A spatial prediction of favorable habitat and potential population levels
The gray wolf has been protected since 1974 under the U.S. ESA of 1973. However, a recent revision of wolf taxonomy considers the eastern timber wolf to be Canis lupus lycaon. This subspecies is now considered extinct in in the eastern United States but extant in southeastern Canada. A restored population of this subspecies in the Northeast may be more important for its persistence in the United States than previously assumed because the recovering wolf population in the upper Midwest is not C.l. lycaon....
Because wolf recovery elsewhere has progressed successfully, there is increased focus on the Northeast. Attention is especially beginning to focus on the region from Upstate New York to northern Maine, a location identified for a potential second population of gray wolves separate from Minnesota. A second, separate population outside Minnesota is specified for official recovery of the wolf in the East. If the second population is assumed connected to Minnesota (e.g. located in Wisconsin and Michigan) the population must be >100 animals in a >12,800 sq. km area for at least five years. If the second population is more distant from that in Minnesota (e.g. the Northeast), the population must be at least 200 wolves in at least a 25,600 sq. km area....
To assist recovery planning in the Northeast, more precise delineation of areas suitable for wolves is required, as are estimates of the potential populations these areas may eventually contain. Recent work suggests that the several hundred animals previously proposed as constituting a viable wolf population may not be adequate when long-term evolutionary potential and viability are considered. In light of this evidence, assessing potential habitat area and potential population size is critical for conservation planning....
Potential Habitat Area and Distribution in the Northeast
Applying our logistic model to data from the Northeast produced a spatially explicit map of potential habitat (Figs. 2, 3) that differed from the previous, generally estimated areas (Figs. 1, 2), and the model assigns predicted probability levels of habitat favorably (Table 1). In the Adirondack Region of Upstate New York, our favorable habitat projection...is considerably less (-34%) than suggested previously. Conversely, potential habitat in Maine is considerably greater (32%) by our estimate than suggested previously....Our model also identifies additional areas in New Hampshire. We also identified habitat in Vermont where potential wolf habitat had not been previously delineated. This habitat occurred primarily along the Green Mountains, which are in the center of the state (Figs. 2, 3)....Maine has the most habitat of the 4 states, the greatest proportion of habitat (65%) in the most favorable class, and the next largest amount (23%) in the second-best class.
Potential Wolf Populations
The prey data combined with the methods of Fuller (1989) and Fuller et al. (1992) yielded a spatially explicit estimate of the potential spatial abundance and distribution of wolves in likely habitat, if the landscape were to be colonized and saturated with wolves at levels known to occur with prey levels that now exist (Figs. 5, 6). The overall area we have delineated in the Northeast has a potential wolf population of 1,312. The potential wolf population in the Adirondack Region could reach approximately 180....Maine has a potential for a total wolf population of approximately 952....New Hampshire has a potential wolf population of 99....The state of Vermont has a potential wolf population of 62....The largest contiguous area of habitat extends from Maine to New Hampshire and into the northeastern corner of Vermont (Fig. 2) and has potential for a wolf population of approximately 1,070....
Comparison of Habitat with the Midwest
The area of potential wolf habitat we have identified significantly exceeds the minimum of 25,000 sq. km specified for a viable population separate from Minnesota. The area we have identified in Maine ((47,372 sq. km) covers more than one-half of the state and nearly equals the area occupied by the large, self-sustaining population in Minnesota (50,200 sq. km). The 16,020 sq. km in New York exceeds the favorable habitat in Wisconsin (15,248 sq. km) where wolf recolonization has been occurring for nearly 20 years....
The mapped results of the model also clearly indicate important spatial distribution characteristics of the favorable habitat in the Northeast. For example, unlike earlier estimates, the large area of habitat in Maine is shown to be contiguous across the state from west to east (Figs. 1, 2). This contiguous habitat also extends into New Hampshire and Vermont, and additional new habitat is also identified as suitable around the White Mountains of New Hampshire (Figs. 1, 2). This large contiguous area across the 3 states (53,837 sq. km) has important implications for the viability of an eventual wolf population because many potential recovery areas are too small to maintain a wolf population large enough for long-term viability, especially if these areas are isolated from Canada....
Comparison of Wolf Density Estimates with the Midwest
....[P]otential wolf density estimates for the Northeast states are lower and more spatially variable than those we derived from the Lake States because of significantly lower productivity in the Northeast as represented by prey abundance (Fig. 4)....However, prey are still abundant in the Northeast and, because of the extensive habitat area in the region as a whole, our estimate of a total potential wolf population of 1,312 is near our projected number of 1,424 for northern Wisconsin and upper Michigan.
Wolf Restoration, Forest Biodiversity, and Management
High deer densities are an important positive factor in wolf recovery because prey density influences wolf population size, survival, and reproductive success. However, these high deer populations are an artifact of highly altered forest ecosystems that are undergoing extensive harvesting at frequent intervals and provide ideal deer forage and habitat. While wolves are often considered wilderness animals, we now know they are also adaptable to semiwild regions with adequate prey, if they are not killed by humans. Ironically, the high deer populations that assist wolf recovery occur in semideveloped, human-dominated landscapes where wolf mortality is high due to intentional and accidental killing of wolves....
....The Northeast has great potential for successful wolf restoration and, given experience elsewhere, wolf recovery may be inevitable whether or not they are actively introduced. Radiocollared wolves in the Lake States have dispersed over 600 km across a largely agricultural landscape and may find their way into the Northeast over long distances from Canada. In our analysis, we have assumed that less favorable areas will not contain any wolves, as occurred in our Midwest habitat and population projections. Further, we also did not include important secondary prey species such as beaver (Castor canadensis) or snowshoe hare (Lepus americanus) in our calculations. The population estimates we have derived may therefore be conservative, given wolf reproductive potentials and their adaptability. If a significant source population of wolves eventually establishes in the large contiguous habitat of Maine, less favorable habitat may also become occupied by wolves....Planning for wolf restoration in the Northeast should...keep in mind the conflicting goals that may occur in restoring a top predator that is dependant on unprecedented levels of deer abundance. Such deer abundance has significant negative effects on the northern forests, a region that remains a highly altered, human-dominated ecosystem.
Fig. 1: Officially designated primary gray wolf population range and official habitat in Minnesota, secondary population area in Wisconsin and Minnesota, and potential population locations in New York and Maine (redrawn from U.S. Fish and Wildlife Service 1992)
Fig. 2: Habitat favorability in the northeastern United States based on the logistic regression model from Mladenoff et al (1995).
Fig. 3: Amount of potential wolf habitat in the probability classes from Figure 2 for (a) Upstate New York, (b) Vermont, (c) New Hampshire, (d) Maine and (e) a-d combined.
Table 1: Habitat probability classes and habitat area (sq. km) from the logistic regression model for the 4-state region of the northeastern United States.
Fig. 4: Maps of (a) deer abundance, (b) Moose abundance, and (c) combined map of deer-equivalent prey units (DEPU) available for wolves.
Fig. 5: Map of potential wolf density and spatial distribution in the northeastern United States based on a combined analysis in Geographic Information Systems (GIS) of derived favorable habitat (Fig. 2) and prey abundance (Fig. 4).
Fig. 6: Potential cumulative wolf population for the northeastern United States: (a) Upstate New York, (b) Vermont, (c) New Hampshire, (d) Maine and (e) a-d combined, based on habitat quality classes (Figs. 2, 3) saturated at projected wolf density levels (Figs. 2, 5).