Effectiveness of Wildlife Habitat Linkage as a Tool for Offsetting Effects of Habitat Loss and Fragmentation

Focus Area

Wildlife & Ecosystems


Natural Resources







Research Idea Scope

Problem Statement:
Over the last decade natural resource agencies and transportation agencies have become increasingly aware of the effects that highway and railroad systems have on wildlife and fisheries. The cumulative effects of highways on wildlife have been serious habitat fragmentation, wildlife mortality, loss of habitat, avoidance of nearby areas used by wildlife and increases in human activities and use of rural lands that support wildlife. Much of this impact can be avoided or minimized by state-of-the-art wildlife crossings and other mitigation.
What are wildlife linkage areas?
Biologists and transportation planners now recognize that to maintain wildlife populations and habitats that “wildlife linkage areas” must be identified and managed. Wildlife linkage areas are critical areas for population or habitat connectivity.
Why are linkage areas necessary?
Habitat loss and fragmentation are the two leading causes of wildlife loss and extirpation. Fragmented wildlife habitats have a lower capability to sustain wildlife populations than large, interconnected habitats.
Proposed Research:
Little research has been done concerning wildlife behavior characteristics and various species willingness to approach and use structures necessary to allow animals to approach and cross highways and railroads.
  • Wildlife –Transportation Interaction – Propose studies to assess how to define areas where interaction between wildlife and the transportation facility are likely along transportation corridors. Discern means to predict such locations without site-specific scientific studies. Develop a model to predict locations of likely interaction with wildlife
  • Behavior of animals -Propose studies to address how movement patterns of various species react to highways, wildlife crossings and related infrastructures and how wildlife reactions are effected by topography, habitat character and the transportation corridor. Many aspects need clarification including the effects of traffic noise, traffic volume, and traffic speed on wildlife behavior.
  • Terrain and habitat features -Propose studies to assess how terrain and habitat features enhance or detract from use of crossings and associated linkage areas. What is the most effective terrain and habitats characteristics to place crossings and linkage zones for various species and multiple species?
  • Maintaining Connectivity – Propose studies to assess where and how to best maintain connectivity within an established linkage zone where portions of the linkage zone may be compromised by changing land uses.
  • Fencing – Propose studies to determine how fencing be used to guide animals into crossings structures? What is the most effect height and mesh designs for various species encountered? Basic information is needed for a wide range of species on appropriate fencing from amphibians, reptiles, small mammals and larger species like elk, moose, bears and deer.
  • Wildlife Crossing Structures – There are a wide variety of wildlife crossings. Propose studies to determine: Which are the best for common species like deer, elk, small mammals, reptiles and amphibians? What are the best structures for multiple species? How effective are existing structures in promoting wildlife crossings? What are the most cost-effective designs? How can existing crossings like bridges and culverts be modified to facilitate wildlife movement? And, which designs are best for specific species such as threatened, endangered or sensitive species affected by highways? What are design elements that generally enhance wildlife use of structures such as natural light and size.

TERI Administrator Note (June 2007):
NCHRP – Evaluation of the Use and Effectiveness of Wildlife Crossings, NCHRP Report 25-27 (2007)


Every year, the costs of personal injuries and property damage resulting from animal/vehicle collisions are considerable. Various means have been employed to mitigate these collisions, with varying degrees of success. In recent years, highway agencies have placed a growing emphasis on protecting the environment. While many smaller species of animals do not pose a threat to vehicles through collisions, they experience significant habitat loss and fragmentation as a result of roadway alignments. Transportation corridors limit the natural movement of wildlife, affecting individual species and ecosystems. There has been considerable research on the provision of wildlife crossings, but there is a lack of data on their effectiveness and on the methods most effective for a particular species in a particular landscape. It also appears that crossings may work well for one species but not for others. A recent international scan on wildlife habitat connectivity documented various strategies and designs used in Europe to improve the connectivity of wildlife habitats. Developing successful designs, methods, and strategies to make roadways more permeable to wildlife is but one aspect of managing highways to avoid or minimize affects to the natural environment and maintaining safety for motorists. There is a need to provide state DOTs with guidance on the use and effectiveness of wildlife crossings to mitigate habitat fragmentation and reduce the number of animal/vehicle collisions on our roadways. The objective of this project is to develop guidelines for the selection (type), configuration, location, monitoring, evaluation, and maintenance of wildlife crossings.

Montana DOT – Wildlife-Highway Crossing Mitigation Measures & Associated Costs/Benefits: A Toolbox for Montana Department of Transportation (2007)

The objective of this project is to aid the Montana Department of Transportation (MDT) with the decision-making process regarding the choice of mitigation structures that reduce animal-vehicle collisions, and provide habitat connectivity for wildlife, for current and future projects. Reducing animal-vehicle collisions and improving habitat connectivity for wildlife across roadways are important factors to consider in highway construction or improvement projects for human safety, economic and ecologic reasons. The estimated 725,000 to 1,500,000 collisions between motor vehicles and wildlife result in more than 200 human fatalities, 29,000 human injuries and over 1 billion dollars in property damage in the United States alone each year. In addition, highways can be a movement barrier to many species, causing habitat fragmentation and, sometimes, reduced survival probability for the population concerned. Engineers and biologists have tested a variety of potential solutions to the safety, economic and ecologic conflicts between wildlife and highways. Many years of work have resulted in substantial knowledge about the application and effectiveness of a wide array of mitigation measures deployed worldwide. However, knowing which mitigation measures address a particular problem, and which would be suitable given local circumstances can be challenging. MDT has contracted with the Western Transportation Institute (WTI) to provide an overview of mitigation measures that reduce animal-vehicle collisions and allow animals to cross the road safely.

FHWA Report FHWA-PL-02-011Wildlife Habitat Connectivity Across European Highways 2002

Habitat and wildlife resources around the world have diminished to the point that transportation agencies are being asked to address impacts to these resources when implementing improvements to transportation systems. The Federal Highway Administration (FHWA), American Association of State Highway and Transportation Officials (AASHTO), and the National Cooperative Highway Research Program (NCHRP) sponsored an international technology scan to learn what actions are being taken in Europe to address habitat and wildlife issues. A delegation of federal, State, and conservation group representatives visited Slovenia, Switzerland,
Germany, France, and the Netherlands to observe and document efforts in Europe.

As a result of the trip, the team formed conclusions and recommendations for U.S. applications in the areas of policy, communications, guidance manuals, and research. In particular, the group recommends (1) including wildlife/transportation issues in the FHWA and AASHTO strategic plans; (2) creating a central source of contact for international exchange of information; (3) developing a number of guidance manuals pertaining to assessment methodologies, interagency coordination, terminology, and structures design; and (4) using pooled funds to study connectivity needs for all types of wildlife; and (5) funding a national connectivity study.

Suggested By

2002 Research Needs Conference Idea Tom Pettigrew Director of Engineering Northern Region USDA, Forest Service

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