Assessing the efficacy of wildlife underpasses in mitigating amphibian road mortality: A case study from the northeastern United States

Abstract

Roads pose significant threats to wildlife populations worldwide, leading to habitat fragmentation and high mortality rates among various species. Mitigation strategies such as wildlife underpasses have been implemented to alleviate these impacts, yet few studies have assessed their effectiveness before and after implementation. We conducted a case study in the northeastern United States to evaluate the efficacy of a wildlife underpass complex in mitigating amphibian road mortality. The study area encompassed a 1.3 km stretch of road, where two underpasses were constructed to facilitate amphibian passage. Through a comprehensive survey spanning five years pre-construction and seven years post-construction, we collected data on amphibian mortality and environmental factors. Linear mixed-effects models were used to assess changes in mortality rates before and after underpass construction using a before-after control-impact design. Our findings indicate a substantial reduction in mortality across the entire amphibian community and for non-arboreal amphibians within treatment areas post-construction. While arboreal amphibian mortality decreased, the difference was not statistically significant. The underpasses effectively facilitated amphibian movement. Overall, our study provides empirical evidence of the effectiveness of wildlife underpasses in reducing amphibian road mortality, highlighting them as a potentially important conservation action. These findings underscore the significance of incorporating underpass structures into transportation planning and infrastructure development to mitigate negative impacts on wildlife populations. Moreover, our study contributes valuable insights for future research and informs policy initiatives aimed at enhancing habitat connectivity and safeguarding vulnerable amphibian populations in environments bisected by roadways.