The Case for Crediting Wildlife Crossings
By Grace Edinger
Across the country, wildlife habitat has been increasingly segmented by the development of highways. State departments of transportation (DOT) and departments of natural resources across the country struggle with the costs associated with wildlife-vehicular accidents, as well as the associated deaths (both human and wildlife). With the average annual number of vehicle miles traveled steadily increasing, these agencies have turned to creating wildlife crossings, which are intentional pathways for wildlife to safely cross roads and highways via over- or underpasses. These structures have been effective thus far, but there is difficulty in valuing the benefits associated with creating crossings. An innovative way to further reduce accidents, protect wildlife, and provide additional economic co-benefits would be to institute mitigation crediting systems for wildlife connectivity.
State DOTs have recently begun thinking about creating wildlife connectivity at the beginning of project plans, recognizing the reduction in accidents and benefits to endangered or threatened species. By creating a standardized way to value these structures, mitigation crediting would promote the construction of these projects, comply with mitigation permitting requirements (ESA, NEPA, etc.), and significantly reduce vehicular accidents associated with wildlife. California recently introduced AB-2344 Wildlife Connectivity: transportation projects which will help create a standardized approach and communication strategy between California’s DOT and the state Department of Fish and Wildlife. This effort is encouraging, and bodes well for other states to follow suit.
Samanns et al. (2020) advocates for creating an advanced crediting system, whereby credits are generated in advance and applied at a later date to mitigate unavoidable impacts of future projects, satisfying permitting conditions. This way, state DOTs can buy credits to mitigate future transportation projects, creating a mitigation bank of wildlife connectivity credits.
How might we go about determining the worth of wildlife connectivity? What does one wildlife connectivity credit actually mean? There is no precedent yet; no standardized or common metrics are used in the United States. Four viable options have been discussed:
Condition-based connectivity metrics are based on the physical attributes of the system (the highway or surrounding ecosystem). These metrics include acres of highway footprint benefited by crossing zone, number of highway lanes, acres of focal species’ habitat impacted, etc. These metrics use geographic area or other physical factors as a proxy for focal species counts. The assumption is that a greater geographic footprint served equates to more animals saved, which may not always be the case.
Function-based connectivity metrics determine the functional output of the wildlife crossing for the focal species. For example, function-based metrics include increases in genetic diversity, number of animals seen crossing, and changes in migration patterns. This would require monitoring of species’ movement, population dynamics, etc.
Model-based connectivity metrics use predictive modeling to determine credit value. In order to be effective, robust empirical data needs to be available to validate and create accurate predictions. For example, this has been shown to work well for big game species whose migration and population dynamics are well monitored and can be extrapolated with confidence, creating accurate models.
Avoided cost metrics look at co-benefits of wildlife connectivity to determine credit value. For example, costs associated with wildlife-vehicular accidents are quantifiable and provide an easy way to determine the cost avoided by creating safe connectivity. In this case, the money saved from picking up fewer carcasses and/or from fewer car accidents would be used to determine credit value.
There is consensus among state DOTs and natural resource agencies that wildlife connectivity provides a direct benefit to wildlife, as well as improved highway safety. Creating a mitigation bank for wildlife connectivity will take a concerted effort to determine credit valuation metrics and success measures, but the effort has the potential to pay off immensely, both economically and environmentally.