More than 10,000 tons of wild mammals are killed on Brazilian roads yearly: Assessing the impacts and conservation implications of wildlife-vehicle collisions
Written by Fernando A.S. Pinto
Atlantic Forest National Institute - Instituto Nacional da Mata Atlântica (INMA). Science Technology and Innovation Ministry
November 13th, 2023
Brazilian federal road (BR-354) bisects Atlantic Forest montane remnants, a hotspot for biodiversity conservation. Photo by Fernando Pinto.
Road mortality overview
We identified and reviewed a total of 62 scientific papers from Brazil that reported roadkill data in order to quantify the overall scale of the problem and its impact on wildlife conservation. A total of 11,817 individuals were reported killed in the 62 studies, with a total of 738 observed mortality rates presented. A total of 62 mammal species were recorded as roadkill, which represents ~60% of all medium- and large-sized mammal species that occur in Brazil. The results differed among species groups - just 15% of primate species were recorded as roadkill compared to 92% of carnivores. Of significant concern was that carnivores also represented 37% of all road-killed mammals. The crab-eating fox was the species most frequently recorded as roadkill across all studies (n = 54; 84%), with roadkill rates ranging from 0.001 to 1.121 individuals/day/100 km of road (Figure 1).
Based on the observed roadkill rates, we estimated that the mortality of medium- and large-sized mammals in Brazil could reach almost 9 million animals per year This result represents more than 10,000 tons of mammals lost per year in Brazil due to wildlife-vehicle collision. The white-eared opossum and the Molina’s hog-nosed skunk showed the highest estimated roadkill rates, with an average mortality of more than 220,000 individuals/year for the opossum and 112,000 for the skunk. Anteaters were also particularly vulnerable with two species - the threatened giant anteater and the southern tamandua - ranked in the top 15 species with the highest estimated roadkill rates.
Figure 1. The Crab-eating fox is widespread in South America, relatively common throughout its range, and classified as Least Concern according to the IUCN Red List. The species occupies most habitats including savanna, cerrado, forests and also anthropogenic landscapes like deforested and urban areas. No precise estimates of population sizes are available, but populations generally are considered stable. (Photo by Fernando Pinto)
Conservation status of species impacted by roadkill
Almost 30% of the species subjected to roadkill in Brazil are listed as “threatened” or “near threatened” on the IUCN Red List of threatened species. Additionally, the IUCN Red List indicates that more than half of the road-killed mammals (53%) showed declining population trends, with a further 24% having unknown status about the direction of their population trends. Importantly, this indicates that mortality from wildlife-vehicle collision is likely contributing to the decline of many mammal species in Brazil. Further studies focusing on the implications of roadkill at population levels is urgently required.
Medium- and large-sized mammals play important ecological roles including predator-prey interactions, seed dispersal, and frugivory. These losses at the population level can increase regional extinction rates leading to important consequences on ecosystem functioning (e.g., defaunation), especially in tropical areas such as the Amazon Basin and the Brazilian Atlantic Forest. Future studies should urgently focus on identifying where and which species are more vulnerable to additional mortality on roads.
Figure 2. The conservation status of 62 species of medium- and large-sized road-killed mammals in Brazil (upper panel) and population trend (lower panel). Data are percentage of species in Brazil and arranged in taxonomic groups. The number of species recorded as roadkill in each taxonomic group is given in parentheses. The direction of population trend and the conservation status is according to the IUCN Red List – VU = vulnerable to extinction, NT = near threatened, LC = least concern, DD = data deficient.
The road ahead
Less than one-third of the mammal species found in our roadkill dataset were considered threatened by roads and railroads on the IUCN red list. In other words, the IUCN does not consider roadkill a threat to most of the mammals that we know are actually impacted by roads. Based on our results, we suggest that roadkill is having a greater impact on wildlife survival than previously thought. Brazil is a continental-scale country with high wildlife richness and an extensive road network, which makes road impact mitigation a big challenge.
Road ecology studies have flourished in Brazil in the last decade, including road mitigation projects. Many projects on the effectiveness of mitigation structures have shown positive results, for example, for the largest terrestrial mammal that occurs in Brazil, the threatened lowland tapir (>250kg) in Cerrado and Pantanal (wetlands) transition areas.
Roadkill is the most conspicuous effect of roads on wildlife, and mortality studies are the first step in assessing impacts; they also are low-cost and relatively easy to conduct. Nevertheless, there is a need to move beyond analyses on mortality and begin understanding how these kills influence population viability and ultimately increase the risk of species extinction to better define priorities for species conservation and road mitigation. Finally, despite the leadership of Brazil on roadkill surveys in South America, the implementation of systematic roadkill surveys focusing on data-deficient locations such as the Amazon and Caatinga biome is also crucial.
Author information
Fernando A. S. Pinto - asp.fernando@gmail.com
Atlantic Forest National Institute - Instituto Nacional da Mata Atlântica (INMA). Science Technology and Innovation Ministry - Ministério da Ciência Tecnologia e Inovação (MCTI), Brazil.
Source citation
Pinto, F. A. S., Cirino, D. W., Cerqueira, R. C., Rosa, C., & Freitas, S. R. (2022). How Many Mammals Are Killed on Brazilian Roads? Assessing Impacts and Conservation Implications. Diversity, 14(10). https://doi.org/10.3390/d14100835
Editor:
Yun Wang
Cite this summary:
Pinto, F.A.S. (2023). More than 10,000 tons of wild mammals are killed on Brazilian roads yearly: Assessing the impacts and conservation implications of wildlife-vehicle collisions. Edited by Wang, Y. TransportEcology.info, Accessed at: https://transportecology.info/research/assessing-impacts-wvcs-brazil-roads
