COVID-19 lockdowns and citizen science data reveal species traits most vulnerable to mortality on roads

This blog post is provided by Sarah Raymond and tells the #StoryBehindthePaper for the paper ‘The impact of the COVID-19 lockdowns on wildlife-vehicle collisions in the UK’, which was recently published in Journal of Animal Ecology. In their study, Sarah and colleagues utilize the reduction of traffic due to COVID-lockdowns and citizen science data on roadkill to study which traits make species vulnerable to being killed by vehicles.

Wildlife are killed in their millions on roads every single year in wildlife-vehicle collisions (WVCs). Iconic British species such as badgers, foxes and hedgehogs are frequently recorded as roadkill in the UK, and for some species WVCs are one of the leading causes of mortality and population decline. WVC risk is not equal for all species; previous observational studies have found that ecological traits, such as diet, body size and home range, can influence the likelihood of species being involved in WVC. However, it has never before been possible to test these findings via perturbation, i.e. by removing or reducing the number of vehicles on roads.

European hedgehog involved in a wildlife-vehicle collision. Credit: Wildlife First Response, UK

The COVID-19 pandemic saw strict lockdown restrictions imposed in the UK. The consequence of this unprecedented social pause was dramatic reductions in traffic by up to 50% during the two major UK-wide lockdowns from March-May 2020 and December 2020-March 2021 (Fig. 1). The subsequent reduction in human activity caused a global quietening and has been coined the “anthropause”. These restrictions also limited scientific research, with many scientists unable to continue their typical fieldwork; however, a number of citizen science research projects, which rely on members of the public to submit data or carry out surveys, continued to run. Using citizen science reported WVC data for the 19 most reported species from ‘The Road Lab’ project, we were able to investigate which traits received a reprieve during lockdowns and so identify the species at a higher risk of being involved in WVC under normal traffic conditions.

Figure 1: Driving direction requests to Apple Maps declined dramatically during two major UK-wide lockdowns (highlighted in green) compared to a pre-COVID-19 baseline (from January 2020). The first lockdown saw the greatest reduction in direction requests (up to 70%). Driving direction requests are used here as a proxy for traffic levels. Data taken from Apple Maps COVID-19 Mobility Trends Reports

We took WVC reports from the two lockdowns and compared these to reports from the same periods in previous years (2014-2019), in the context of ecological traits previously identified in other studies as determinants of WVC risk. On average, WVC were 80% lower during lockdowns than would have been expected under normal conditions, but this was not surprising given the reduction in traffic and that citizen scientists were spending most of their time at home, leading to not only fewer WVC, but also likely a reduction in the number of people actually reporting roadkill.

To overcome the erroneous conclusions that could be associated with comparing absolute counts of WVC before and during lockdowns we used compositional data analysis. Through this, we found that there were proportionally fewer WVC reports during lockdowns for nocturnal mammals, animals that visit urban environments compared with urban residents, mammals with greater brain mass, and birds with longer flight initiation distances (i.e. the distance at which they flee an oncoming threat – in this case, a vehicle) (Fig. 2). Badgers, foxes and pheasants, that all exhibit some of these traits, are therefore species that are potentially more likely to experience the highest levels of mortality under normal traffic conditions.

Figure 2: On average WVC reports declined by 80% during lockdowns compared to previous years with proportionally fewer WVC involving those species with the four ecological traits outlined above. If the point falls above the dashed line, it indicates that relatively more animals with the trait above the graph were reported as WVC during lockdowns compared to previous years, and vice versa for points falling below the line.

This study enabled us to seize the opportunity of COVID-19 lockdowns, and associated reductions in vehicle use, to understand which traits make species vulnerable on roads. The UK has ~39 million car owners, and 78% of all land is within just 1 km of the 400,000 km of roads that intersect the landscape; therefore anthropogenic infrastructure may even be acting as an evolutionary driver or selective force for certain species and traits. Identifying those ecological traits that are associated with WVC-risk could help to identify where conservation efforts could be focused to reduce the impact of human infrastructure on British wildlife.

Read the paper

Read the full paper here: Raymond, S., Spencer, M., Chadwick, E. A., Madden, J. R., & Perkins, S. E. (2023). The impact of the COVID-19 lockdowns on wildlife–vehicle collisions in the UK. Journal of Animal Ecology, 00, 1-12

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