Number of wild animals killed on US roads fell by 58% as traffic reduced due to coronavirus lockdown: Study
As the coronavirus pandemic continues to ravage the US, wildlife is benefiting with roadkill taking a massive drop in some parts of the country due to lockdown and subsequent reduction in traffic. According to researchers, traffic on US roads fell by as much as 73% during the peak of the stay-at-home orders in March and April. During the same period, wildlife killed in collisions on US roads dropped by up to 58%.
“Using traffic and collision data from California, Idaho and Maine, we found that wildlife-vehicle conflict (WVC), including for mountain lions in California, has declined by about 21-58% following the various government stay-at-home orders,” says the research team from the Road Ecology Center at the University of California, Davis, in their analysis.
In the current report, the authors investigated potential changes in impacts on wild and domestic animals from reduced traffic in three US states with advanced systems for tracking wildlife-vehicle conflict (WVC): California, Idaho, and Maine. For California, they used data collected by the Road Ecology Center’s California Highway Incident Processing System (CHIPS) from California Highway Patrol reports. For Idaho, the team downloaded data from the Idaho Fish and Wildlife Information System (IFWIS) and communicated the use of the data to the Idaho Department of Fish and Game. For Maine, the team requested and received data from the Maine Department of Transportation.
The date of the stay-at-home order, or similar guidance, varied among states: for California, it was March 20, for Idaho March 26, and March 31 for Maine. The research team compared total numbers and rates of wildlife-vehicle conflict before and after the respective orders for each state. From early March to mid-April, these orders have resulted in up to 71%, 63%, and 73% reduction in driving, as measured by vehicle miles traveled in California, Idaho, and Maine respectively, shows analysis.
“State highway travel in the three states declined 20-60% between early March and mid-April and travel on all roads in California, Idaho and Maine declined by up to 71%, 63% and 73%, respectively, suggesting that the majority of people were taking guidance about staying at home seriously. We used carcass and crash reports to calculate the change in daily collision rates from the four weeks before stay-at-home orders going into effect, to the four weeks after. There was a statistically significant reduction in the number of large wild animals killed per day on California, Idaho and Maine state highways that coincided with the reduced traffic following state stay-at-home guidance,” say experts in their analysis.
They explain, “Although rates of wildlife-vehicle conflict naturally vary by season, the change from one month pre-stay-at-home orders to one month post-order only occurred in 2020 and not 2015, 2016, 2017, 2018 or 2019, suggesting that the reduction was associated with the reduction in traffic. In the three states, this could amount to 5,700 to 13,000 fewer large mammals killed on roads per year, and in California, 50 fewer mountain lion mortalities on roads per year. This represents the first evidence of reduced rates of WVC in response to the reduced travel by many Americans in response to Covid-19 related mitigation efforts.”
Overall, the analysis suggests that due to reduction in traffic, fatal collisions with wild animals such as mule deer, white-tailed deer, moose, elk, black bear, coyote and mountain lion dropped by 21%, 38% and 44% for California, Idaho and Maine respectively. The number of animals killed decline from 8.4 to 6.6 per day in California, from 8.7 to 5.4 daily in Idaho, and from 15.2 to 8.4 animal deaths in Maine daily. There were similar statistically-significant reductions in impacts on domestic animals, including cows, horses, sheep, goats, dogs and cats for California, say researchers.
Mountain lions in California experienced a 58% reduction in deaths on roads at a time when the state is considering legal protection for the species, in part because of lion-vehicle collisions. Mountain lions are reported hit on California roads and highways up to twice per week. In a typical year, this rate either stays constant or increases slightly in the transition from winter to summer. “We found that the rate of mountain lion mortality declined 58% between the 10 weeks before the state order and the 10 weeks after. One significant impact of this finding is the clear link between traffic and rates of mountain lion death. This means that to reduce mountain lion mortality, populations must be protected from traffic, especially in the Bay Area and Southern California where isolated and small populations of mountain lions are at risk of extinction,” write authors.
The team emphasizes that given the five to nine-fold underreporting of large animals involved in collisions with vehicles and the “lack of systematic reporting” of smaller animals killed on roads, the “unintended positive impact of Covid-19” reported by them are likely to be just the “tip of the iceberg” of reduced deaths of wildlife on US roads and highways.
In general, the study did not find any major changes in the distribution of wildlife-vehicle conflict across the states. In other words, the number of animals killed by vehicles seemed to decrease uniformly across all highways. In California, areas around the San Francisco Bay, Sacramento region and Southern California that usually have higher densities of wildlife-vehicle conflict than surrounding areas continued to have higher densities. Similarly in Maine, areas along the I-95 corridor around Portland, Augusta, Bangor and Houlton continued to have higher densities of wildlife-vehicle collisions than surrounding areas, but with lower overall numbers. “Generally, there was no obvious difference between patterns and distribution of wildlife-vehicle conflict density before and after state stay-at-home orders, suggesting an evenly-distributed benefit to wildlife across the states,” says the research team.