High rates of wildlife-vehicle collisions during the COVID-19 pandemic
In total, we found that although traffic volume decreased by> 7% during the pandemic year (with a maximum monthly decline of almost 40%), the absolute number of annual WVCs was largely unchanged. This resulted in significant increases of> 8% in vehicle-wildlife collision rates during the pandemic year, peaking at a> 27% increase nationwide in April 2020. Further studies conducted during the first months of the pandemic have documented similar transient declines in numbers. of WVCs at the start of the pandemic, which then reversed in many jurisdictions as the pandemic progressed and traffic rebounded26.27. We observed a similar pattern during the first five months of the pandemic nationwide (Fig. 2): WVCs first declined during the pandemic along with the decline in traffic volume, but then began to decline. increase to reach reference levels at a faster rate than traffic, possibly due to behavioral delays in wildlife as a result of increased wildlife use of roads. Although based on large-scale data, our research aligns with the claims of studies conducted during27 and before the pandemic3,15,16,28,29 that the relationship between traffic volume and WVCs is not linear.
We postulate that the observed nonlinear relationship between traffic volume and WVCs is the result of greater use of roads and roadsides by certain wildlife species, namely large mammals (Table S1), in response to decreased traffic volume, as previous research has suggested3,14,15,16. This explanation is consistent with the accounts of various wildlife species making increased use of human spaces during the pandemic.17.20.21: with fewer cars on the roads, wildlife could be less diverted from the roads by the noise and light pollution that accompany high traffic volumes9,10,11,20 and perceive the roads as less risky, thus increasing their willingness to attempt road crossings3,8,15,16. Beyond accidentally crossing roads while moving through the landscape8.9, wildlife may be attracted to roads for travel, companions, or other resources8.10.11. Many animals have been shown to use roads to move efficiently through the landscape11.12, and the roads and surrounding areas are relatively open, so wildlife can select roads and road edges for better visibility to find mates, detect predators, or locate prey10.13. Road sides can also provide feeding opportunities and essential nutrients for wildlife through abundant, high-quality early successional vegetation and high salt concentrations.10.11. Thus, the decrease in road traffic during the pandemic may have caused some wildlife species to tolerate the risks associated with roads in order to access the benefits of roads and roadsides.
Another explanation for the observed increases in collision rates is that the driving behavior of humans, rather than animals, changed during the pandemic. With fewer cars on the road, people could drive faster35, making it more difficult for humans and wildlife to avoid collisions3. Preliminary studies conducted across the United States have indeed suggested changes in human driving behavior during the pandemic, with several jurisdictions reporting increased vehicle speeds.35.36. Despite the reported increases in vehicle speed, however, the total number of vehicle collisions (the sum of collisions with wildlife and non-wildlife) reflected trends in traffic volume and declined significantly during the pandemic.37.38. Thus, given that changes in human behavior appear to have had a minimal effect on vehicle collisions overall, it is unlikely that the observed changes in collision rates were due solely to increased vehicle speed. vehicles. Nonetheless, we cannot rule out the possibility that changes in human driving behavior may have contributed to the models documented here, and future work should more explicitly test the relative effects of changes in traffic volume on both human driving behavior. and on wildlife use of space, as well as the resulting impacts on WVCs.
A better understanding of human driving behavior would also help explain our findings regarding changes in traffic patterns during the pandemic. Nationally, the severity of COVID-19 restrictions accounted for much of the variation in changes in monthly traffic volume (R2= 0.968), but the severity of the restrictions had less influence on the changes in annual traffic between states (Tables S3 and S4). The restrictions implemented throughout the pandemic were largely adopted in an effort to minimize travel, and other research has shown these restrictions to be effective in reducing human mobility.18.21. Our state-level results, however, imply that it was not only the restrictions themselves that reduced travel, but possibly the associated anxiety about the risk of contracting the SARS-CoV-2 virus as well. , as has been suggested in other studies21,22,23,24; although we observed the largest drops in traffic volume at the start of the pandemic (Fig. 2A) when the restrictions were most stringent (Fig. S2)21, there was widespread anxiety about the risks posed by SARS-CoV-2 during this time22.23, which probably motivated people to stay home regardless of the restrictions24. Indeed, anxiety and risk perception could explain the relationship between traffic volume and other covariates in our higher models (Table S4). The decreases in traffic were greatest in the most densely populated states (Fig. 4A) and in the states with the highest and lowest disease burdens (Fig. 4B). The risk of transmission of SARS-CoV-2 is higher in more densely populated states due to proximity and frequent interactions between people21. As such, people may have changed their use of the road more in densely populated states than in sparsely populated states due to differing perceptions of the risk of disease transmission.23– although differences in infrastructure compared to population density probably also contributed to this trend39. Likewise, declines in traffic volume in states with larger outbreaks of SARS-CoV-2 may have been caused by an increased perceived risk of contracting the virus.21.23. Alternatively, traffic reductions in low disease burden states could reflect increased compliance with stay-at-home orders, and therefore less possibility of disease spread.40.41; in essence, reductions in traffic volume could be the cause of a locally low disease burden, rather than a consequence. Overall, we postulate that the observed heterogeneity in traffic volume between states is, at least in part, attributed to differences in the perceived risk posed by the SARS-CoV-2 virus.
Regardless of the mechanisms underlying changes in traffic volume and WVCs, our observation that the annual number of WVCs has remained largely unchanged despite substantial declines in traffic volume has implications for the mitigation of WVCs in the future. ‘to come up. More directly, the lack of a change in direction in WVCs suggests that road traffic levels in the United States are currently such that even large declines in traffic volume would have minimal long-term effects on the absolute number of WVCs. As such, decreasing collisions by reducing the volume of traffic would require even larger and more lasting traffic changes than those seen during the pandemic. Since such massive and lasting reductions in traffic are unlikely4.5.6, WVCs in the United States are essentially a fixed cost, both to human society and to wildlife populations. As such, these transient decreases in traffic likely provided minimal respite for large mammals from collision-induced mortality, contrary to speculation that changes in human mobility during the COVID-19 pandemic had effects. substantial positives for wildlife populations by freeing wildlife from direct ubiquity. and the indirect effects of man17,18,19,20,26,27,42.
Short-term reductions in traffic volume may ultimately be detrimental to wildlife species that have increased their use of the road. Although the increases in collision rates that we observed at the start of the pandemic were rapid and correspond to national declines in traffic volume (see also26.27), collision rates remained high even as traffic approached reference levels in July (Figure 2B). If the responses of wildlife to changes in traffic are asymmetrical (i.e.., increases in road use by wildlife following a decrease in traffic occur more rapidly than decreases in road use by wildlife in response to increased traffic), so short-term declines in traffic volume could result in net increases in the number of WVCs over longer periods of time, ultimately proving to be detrimental to certain wildlife populations1.3. Future work should assess the long-term effects of the pandemic on wildlife populations, particularly with regard to collision-induced mortality.17,20,26,27,42.
While the COVID-19 pandemic has made it possible to examine the short-term effects of transient decreases in traffic volume on WVCs, the longer-term effects of expanding human populations, increased road density and overall higher traffic volumes on WVCs are less clear. Similar to the increase in road use for wildlife in response to the decrease in traffic volume theorized here, steady increases in traffic could reduce road use for wildlife in the long run.3,14,15,16; since road traffic indeed increases over time4.5.6, so we might see a decline in WVCs as roads become more efficient at repelling wildlife1,3,14. While these reductions in vehicle-induced wildlife mortality are welcome, it would see roads increasingly serving as barriers to animal movement and gene flow.43, further fragmenting the already disconnected wildlife populations8. Thus, policymakers and planners should invest in infrastructure such as overpasses, underpasses and fences that allow wildlife to safely cross high-traffic roads or direct wildlife to low-traffic areas. risk.8.9. Even substantial short-term declines in road traffic are not sufficient on their own to alleviate wildlife-vehicle conflicts.