Wolves, roads, and highway development

Abstract

Roads are pervasive in the landscape of the United States and have profound ecological effects (Forman et al. 2003). Recent studies estimate that nearly 20% of the United States is ecologically impacted by the public road system and associated traffic (Forman 2000). In general, wildlife is impacted by roads in four major ways: (1) loss of habitat; (2) traffic mortality; (3) inaccessibility to required resources; and (4) division of populations into smaller, isolated subdivisions (Jaeger et al. 2005). Although gray wolves ( Canis lupus ) in the upper Great Lakes region are not impacted by all of these factors, their unique and highly variable relationship to humans creates even more complex relationships with roads than many other wildlife species. Habitat suitability for gray wolves primarily is dependant on two variables: (1) availability of prey, and (2) tolerance of humans who live or recreate near wolves (Mech 1995 ; United States Fish and Wildlife Service 1992 ; Fuller 1995 ; Fritts et al. 2003). However, highways, roads, trails, and other paths created by humans alter that suitability in many ways. Some interactions result in behavioral changes among wolves, while others result in higher mortality. The additional mortality may be directly related to collisions with vehicles on roads, or indirectly related through the intentional or unintentional killing of wolves by those accessing areas inhabited by wolves. Regardless of the mechanism, research in the Great Lakes region has shown that high road densities limit habitat suitability for wolves and that major highway corridors can slow range expansion in recovering wolf populations (Thiel 1985 ; Jensen et al. 1986 ; Mech et al. 1988 ; Mladenoff et al. 1995, 2006 ; Mladenoff and Sickley 1998). In this chapter, we summarize what biologists in the upper Great Lakes region have learned over the past 30 years about the impacts of roads and road densities on wolves, and discuss modifications to future highway projects that may reduce impacts on wolf populations and range expansion. Before we can examine the relationship of wolves to roads, a clear understanding of what constitutes a road is needed. The term "road" is a broad and generic term used to describe a human-created structure to convey vehicles. However, not all roads are perceived as equivalent by wolves. Roads included in this discussion include three distinct categories: (1) structures dressed with hard surfaces (blacktop, reinforced concrete) designed for higher speeds and volumes of traffic (federal, state, and county systems), (2) secondary access (primarily county and rural municipalities) with lightly maintained surfaces (gravel), and (3) public-use unimproved roads, recreation trails, and some logging access trails (maintained by federal, Native American, state, and county conservation agencies). As we discuss later, the type of road combined with traffic volume and regularity of use influence both crossings and use of roads by wolves in the upper Great Lakes region. Despite a myriad of mechanisms influencing wolf interactions with roads, wolves living in the upper Great Lakes region have revealed a surprising and variable adaptability to the presence of roads. The significance of road impacts depends on dynamic factors such as changing human attitudes toward wolves, amount of suitable habitat occupied by wolves, and viability of wolf populations. Therefore, data and analyses presented here are applicable to the upper Great Lakes region. We caution against applying them to other regions or in different circumstances without further testing and validation.