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An overview of methods and approaches for evaluating the effectiveness of wildlife crossing structures: emphasizing the science in applied science


Human activities today often cause landscape habitat fragmentation and blockage of wildlife movements across landscapes and ecosystems. North American and European Union initiatives such as the Transportation Equity Act and COST-341 program have heightened the importance of mitigating the negative effects of roads, such as animal-vehicle collisions and barrier effects. Wildlife crossing structures are being incorporated into some road construction and improvement projects in an attempt to reduce negative effects on wildlife populations. Transportation and resource agencies are becoming increasingly accountable and therefore concerned as to whether highway mitigation measures are functional and perform to expected standards. However, there are presently gaps in our knowledge regarding the effectiveness of wildlife crossings structure applications. One reason for the lack of available information is that relatively few mitigation projects implement rigid monitoring programs with sufficient experimental design. Thus, results obtained from most studies remain anecdotal or descriptive at best. With sufficient lead-time, experimental study designs can provide rigorous assessments of highway impacts and wildlife crossing structure performance pre- versus post-construction. Alternative methods of post-construction assessment can be used if time does not permit for data collection during the pre-construction period. We review past and current methods used to evaluate wildlife crossing structures and examine criteria to consider when evaluating wildlife passage effectiveness. We focus on methods to monitor mammals and summarize representative studies published international journals and conference proceedings. We examine pre- and post-mitigation study designs versus evaluations that base effectiveness solely on post-mitigation monitoring. We make suggestions for conducting quality scientific evaluations that will allow transportation agencies to address the question, “Do wildlife crossing structures work?”

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