OOS 25-2 - Effectiveness of fences in reducing road mortality of ground-dwelling anurans and tree frogs in a Brazilian reserve

In tropical regions, mortality on roads is a highly neglected impact on amphibian populations. In southern Brazil, we estimated more than 7500 amphibians roadkilled from at least 24 species in a single 6-month reproductive season, including four regionally endangered ones, on a single 1-km road bisecting the Mata Paludosa Biological Reserve. For one of these endangered species (the Leaf Frog, Phyllomedusa distincta), roadkill was responsible for 25% of the mortality of the reproductive population from one pond. Animex AMX-SP-40 free-standing fences with a top lip designed for amphibians were installed on this 1-km road segment crossing. This happened after 30 years of discussions among stakeholders (state transport agency, reserve managers, federal environmental agency, environmental consulting company and academic researchers), and the involvement of NGOs and the justice. In a multi-sector collaboration, we monitored road mortality before and after the installation of the fences on the 1-km road segment bisecting the reserve and on a 1-km control road segment without fences during spring-summer seasons. We aimed to assess the effectiveness of the fences in reducing road mortality of two target groups: ground-dwelling anurans and tree frogs. Surveys of amphibian road mortality were carried out on foot, twice a day at dawn and dusk, during seven consecutive days per month in each sampling period (6 months before and 7 months after installing the fences). Before and after data showed that road mortality of ground-dwelling anurans reduced 7 times after the installation of the fences, while road mortality on the control road segment remained high. Meanwhile, road mortality of tree frogs did not decrease after the installation of the fences, showing that these animals can climb and jump over them, even with the top lip. We observed that fences strongly reduced the mortality of ground-dwelling anurans and did not reduce road mortality of tree frogs. The effectiveness of the fences in avoiding mortality varies between groups, but also within each group, as the difference in mortality between control and fenced road segments varies among species. Completely blocking the access of tree frogs to the road is still a challenge, and there is a need for constant vegetation management and fence maintenance. There are at least 16 species of tree frogs of different body sizes being killed on this road, and we are currently experimentally testing different anti-climb lip designs and material textures to block these animals.