Pairing long-term population monitoring and wildlife crossing structure interaction data to evaluate road mitigation effectiveness

Abstract

Roads negatively affect wildlife populations directly as a source of mortality and indirectly through habitat fragmentation, restricted movement, and altered habitat use. Wildlife crossing structures and roadside fencing are two common road mitigation strategies implemented to reduce wildlife road mortalities and maintain population connectivity. Metrics quantifying use of crossing structures by wildlife are often used to determine their effectiveness, but interpreting these metrics can be challenging when local population processes and individual variation in use are not considered. We used over six years of remote camera data, including two years of post-construction data, from a road improvement project in south Texas to evaluate mitigation efforts in the context of long-term felid abundance. Variation in seasonal felid abundance was tied to precipitation in the preceding 12 months, highlighting the importance of accounting for baseline wildlife abundance when measuring structure efficacy. Crossing structure use by felids was positively correlated with abundance estimates, though frequency and consistency of use varied among individuals. Probability of use was related to roadside fencing, canopy cover, time since crossing construction, and presence of water in the structure. Our results suggest that conventional indices of crossing structure effectiveness, such as crossing rates, are more informative when ongoing population processes are considered. By interpreting structure use in the context of long-term abundance trends and individual variation, managers can compare use across sites to better determine factors that influence crossing structure effectiveness and take steps to site, construct, and maintain structures that enable safe wildlife road crossing and promote connectivity.