Road kills in tropical ecosystems: a review with recommendations for mitigation and for new research

Abstract

While roads are indispensable for modern civilization and beneficial for many wildlife species, they have been causing mortality from collisions since high speed chariots were invented 4 000 years ago. Most scientific work about road kill has been done in temperate ecosystems, but some authors have suspected that they have different characteristics in tropical ecosystems. In this review, I summarize publications that focus on road kills in tropical countries from Africa, America, Asia and Oceania. I found 73 studies that focus on tropical road kills. Output increased after 2011 and the most productive countries, in articles per capita, are Costa Rica, Colombia and Brazil. Most studies report that mammals are the main victims, but bird deaths are severely underestimated and amphibians suffer mass mortality in reproductive concentrations. Every road victim is itself a small ecosystem that contains thousands of microscopic species, but “Road Kill Microbiology” is yet to be developed as a new branch of research. No generalization can be made about the role of season or habitat in road kills because pooled data hide individual trends: researchers should keep separate records by age, sex, species, time of day, season and place; otherwise important patterns will be missed. There is not a single study, tropical or temperate, that can completely answer how many animals are killed, where, or when, because many victims are removed by scavengers, end outside the road or are too small to be noticed. Significant contributions from the tropics include emphasis on the ethical use of road kill for research, inclusion of species other than wild vertebrates, study of often overlooked phenomena like hour of day and failed versus successful crossing attempts, and the value of speed control in mitigation. The so-called “citizen science” can identify the most affected species but produces data that are very different from those generated by professional scientists in terms of the proportion of affected groups. Real speed limitation is the simplest effective mitigation measure. Tropical scientists should concentrate on monitoring and experimental studies to fully understand the ecology of road kills and to make a contribution that matches what rich countries do. Rev. Biol. Trop. 66(2): 722-738. Epub 2018 June 01.