The impact of the RS-040 highway on wildlife roadkill patterns in Porto Alegre, Brazil

Road infrastructure has severely affected the environment and wildlife. Understanding and mitigating these effects are essential conservation measures. This study aimed to evaluate fatal wildlife-vehicle collisions along an 80-km stretch of the Tapir Rocha highway (RS-040). Fieldwork was carried out between August 2015 and March 2019. Once a week, two observers were driven along the highway at an average speed of 40 km/h. All dead vertebrate sightings were investigated to document the species, carcass condition, and locations along the roadway. In total, 2,371 wild, domestic and unidentified dead animals were assessed and categorized into 137 species. The most affected classes were mammals (n = 1,223), and birds (n = 704). The most affected wild species were white-eared opossums (Didelphis albiventriss, n = 559), black-and-white tegus (Salvator merianae, n = 129), and coypus (Myocastor coypus, n = 102). The carcass exposure assessments indicated that many (n = 637) animal deaths occurred the night before our arrival and that nocturnal species may also be more vulnerable to roads. Roadkill sightings peaked in the spring (34%) and summer (25%), probably due to reproductive activity and juvenile dispersal. Seasonal variations included a 50% reduction in reptile roadkill rates in autumn winter compared to spring-summer, and a 20-percentage-point increase in the number of mammal road deaths in the winter. Thermally restricted reptile activity, and seasonal changes in carnivore food habits may explain these respective findings. Although most of the road deaths affected abundant and widely distributed species, a decrease in these populations may eventually become a conservation concern.