Roads Threaten Millions of Birds and Mammals in Europe Each Year
Written By Clara Grilo
CESAM - Centro de Estudos do Ambiente e do Mar, Faculdade de Ciências da Universidade de Lisboa
9th November, 2020
Around ~194 million birds and ~29 million mammals could be killed each year on European roads, and some species are particularly vulnerable to additional mortality even with low rates of roadkill.
The main goal of this study was to understand which species are subject to the greatest rates of roadkill and map areas where roads are a major threat to wildlife conservation in Europe. To do this, we compiled 90 studies with records of roadkill in Europe and developed models to estimate rates of roadkill for the unstudied species based on their biological and ecological characteristics.
We found that small-sized species such as Eurasian Tree Sparrow and Southern White-breasted Hedgehog and those which are locally abundant and reproduce frequently (such as species Eurasian Shrew and Eurasian Blackbird) typically have the highest rates of roadkill. In other words, the species with the highest rates of roadkill are, in general, the most common and not of conservation concern. Using this information, we then estimated that ~194 million birds and ~29 million mammals may be killed each year on European roads. Since the European continent has one of the highest densities of paved roads in the world, reaching 2 km/km2 in Central Europe, we were not completely surprised by these findings. For example, we found several systematic roadkill surveys in Europe with very high numbers, such as the Eurasian blue tit in Portugal with 7 individuals killed per km per year and in the Czech Republic, a bat (Nathusius' Pipistrelle) had a roadkill rate of 9 ind/km/year.
When we analyzed the risk of species being vulnerable with additional mortality from roads by modelling the population growth with demographic parameters (e.g. age of sexual maturity, birth rate, longevity), we found that species can be vulnerable to extinction even when few individuals die due to collision with vehicles, because these species cannot compensate for this additional mortality. This was the case for several species of eagles and bats. This means that roads with the highest numbers of roadkill for birds and mammals are not necessarily in the same locations where the species which are most vulnerable to roadkill occur.
In Europe, road safety has been a priority of road planning and design because many people are injured or die each year due to collision with large mammals, mostly deer, wild boar and other ungulates. But from a conservation point of view, the approach must be different, and it should also focus on species which are particularly threatened by the additional mortality caused by roadkill.
We urgently need to move beyond quantification of roadkill and additionally assess the impact of additional mortality on populations. We also need better estimates of roadkill by conducting systematic regional surveys, not just ad-hoc surveys on some roads. We also need better estimates of population size to calculate the proportional loss of individuals from a population. For example, 100 individuals killed per year along a certain road is an almost meaningless statistic from a conservation point of view. However, 100 individuals killed per year out of a population of 200 is a 50% loss, and 100 from a population of 10 000 is a 1% loss. Effective strategies can then be developed when this information is combined with species-specific information about reproduction rates and longevity.
We concluded that the failure to consider how roadkill affects populations may result in misidentifying appropriate sites for mitigation.
Author information:
Clara Grilo CESAM - Centro de Estudos do Ambiente e do Mar, Faculdade de Ciências da Universidade de Lisboa, C2, 2.3.03, 1749-016 Lisboa, Portugal
Email: clarabentesgrilo@gmail.com
Source:
Grilo C, E. Koroleva , R. Andrášik, M Bíl, M. González-Suárez (2020). Roadkill risk and population vulnerability in European birds and mammals. Frontiers in Ecology and Environment, 18(6), 323-328. https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/fee.2216
Editor:
Rodney van der Ree
Cite this summary:
Grilo C. 2020. Roads Threaten Millions of Birds and Mammals in Europe Each Year. Edited by van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/roads-threaten-millions-of-birds-and-mammals-in-europe-each-year [Date accessed].