Maine recorded 44 percent fewer roadkill victims, according to the report from the University of California at Davis. California’s deaths-by-bumper dropped 58 percent for mountain lions, and 21 percent overall. If a similar drop occurred across the United States, where some estimates suggest as many as 1 billion wild animals are killed by vehicles each year, about 200 million creatures’ lives would be spared annually.
“That’s a huge, huge benefit to wildlife populations across the country,” said Fraser Shilling, co-director of the Road Ecology Center at UC Davis, who helped produce the report — which, he emphasized, does not suggest that the global pandemic has been a good thing.
“From a humanity point of view, it sucks,” Shilling said. “But from a science point of view, it’s all interesting.”
The report relied on data collected regularly by the three states’ departments of transportation, highway patrol units and wildlife agencies. With information dating back to 2015, the scientists were able to compare what happened during shutdowns in each state to normal roadkill numbers. They found no significant difference between what happened before or after the stay-at-home orders, but during that low-activity window, the results were striking.
In just California, Idaho and Maine, the declines would translate to 13,000 fewer large mammal carcasses along roads. In California, a state that is considering extending endangered species protections to some mountain lion populations that are often hit by vehicles, less traffic could save about 50 big cats a year, the report found.
The report relied on statistics from only three states because they collect solid roadkill data — and even those numbers are likely to be significantly underreported, Shilling said. The Davis study does not account for the deaths of smaller creatures such as raccoons, opossums, turtles, snakes or songbirds. Loop in all of those animals and scale it across the nation, and the true toll of car strikes could rocket into the hundreds of millions.
Shilling, an ecologist who studies the impact of transportation systems on nature, said the sudden and extreme dip in road traffic presented scientists with an experiment that could never be carried out in typical times. Fortunately, data sampling already in place allowed them to make use of the unprecedented circumstances.
Last month, more than a dozen researchers in several countries published a commentary in the journal Nature Ecology and Evolution calling on scientists to investigate how the coronavirus pandemic and its reverberations could allow for precisely this kind of research.
Normally it’s extremely difficult to disentangle how humans affect animal movements and behaviors, said Francesca Cagnacci, an animal ecologist at the Edmund Mach Foundation in Italy and senior author of the commentary. Many variables could explain an outcome or cast doubt on the level of human influence on an animal behavior.
But the coronavirus shutdowns have offered new signs of our sway, as well as opportunities to gather evidence. This is why scientists were eager to study how a lack of human observers might affect large swarms of mating fireflies this summer. It’s also why the Centers for Disease Control and Prevention issued a warning after city-dwelling rats appeared to be acting more aggressively as their supplies of restaurant garbage shriveled.
Cagnacci said that the shutdown underscores the importance of ongoing studies that record observations before anything unusual happens — even though it can be unclear what the results will be good for.
“Sometimes it’s very difficult to explain to a funding agency or to the general public why it is important to conduct baseline observations about what’s happening in ecosystems,” she said.
For Shilling, tracking large animals killed by vehicles has revealed the weighty toll of human transportation on wild animals. This translates to costs for humans: An earlier report from the Road Ecology Center found that wildlife-vehicle collisions in 2018 cost Californians $232 million in medical bills, lost wages, vehicle damage and emergency response costs.
That sort of information is important when trying to determine — and persuade policymakers and the public about — the value of erecting roadside fences or building overpasses that allow animals to bypass highways, said Marcel Huijser, a road ecologist at Montana State University’s Western Transportation Institute.
Such “animal exclusion” projects can carry hefty price tags. But there are many stretches of road in the United States where it’s actually more costly to do nothing, Huijser said.
Road ecology “has three pillars,” Huijser said. “Human safety, biological conservation and economics.”
Huijser said the Davis findings on roadkill did not surprise him. More interesting, he said, is that the number of animals killed did not drop at the same rate as the decrease in traffic. He said he suspects that this is because not all traffic is equal.
Essential travel did not stop, including the transportation of goods, which tends to continue around-the-clock. At the same time, people who might normally have been out shopping or commuting during the day stayed home.
“That could explain why we have a nonlinear reduction in dead animals,” Huijser said. “Because they’re more likely to be hit around dusk and dawn and during the night compared to during the day.”
Like the wild boar returning to Barcelona and the sea turtles flourishing on empty beaches in Brazil, at least some American wild animals seem to have caught a bit of a break while the novel coronavirus spread.
Simply driving less for a few weeks is “probably the biggest conservation action that we’ve ever taken as a country,” Shilling said. “We did it accidentally. But I can’t think of another action in the last 50 years that has that kind of consequences for that many animals.”