Roadkill rates drop as COVID-19 keeps motorists at home

The COVID-19 pandemic has been horrendous on so many levels, but we’ve at least had a few silver linings to cling to amid its global ravages. The dramatic contraction of human activity – the “anthropause,” as a just-out paper calls it – has, for example, given wildlife some extra breathing room and quiet.

A new study suggests a related benefit of our altered behaviour during the outbreak: fewer critters getting squashed on the pavement. Researchers at the University of California-Davis’s Road Ecology Center have shown that reduced traffic during the stay-at-home phase in three US states translated to less roadkill, at least of large mammals such as deer, elk, moose, black bears, and pumas.

Research has shown that reduced traffic during the COVID-19 stay-at-home phase in three US states translated to less roadkill.

The states the study focused on – California, Idaho, and Maine – all have robust mechanisms for tracking wildlife-vehicle collisions (WVC), and all instituted one form or another of stay-at-home/shelter-in-place guidance in late March to try to curtail the spread of COVID-19.

Examining traffic data, the researchers found that, between early March and mid-April, California saw a 75% reduction in travel on all roadways, Maine a 73% reduction, and Idaho a 63% reduction. Over the same period, the number of reported vehicle collisions with large mammals went down in those states by 21%, 44%, and 38%, respectively.

Statistics from previous years show this springtime stretch in the U.S. typically sees WVC rates either holding steady or increasing. That, coupled with basically uniform reductions in reported roadkill across the states’ transportation corridors during the period, suggest the diminished WVC are likely indeed due to fewer people behind the wheel.

Accounting for the fact that WVC are significantly under-reported, the study’s authors suggest the findings might shake out to "5,700 to 13,000 fewer large mammals killed on roads per year" in the three states.

Ungulates like white-tailed deer are among the most common big roadkill recorded in the US. Image © US Air Force photo/Mike Kaplan

The authors note that trends similar to those seen in California, Idaho, and Maine are likely to have occurred in other parts of the US where the outbreak prompted similar slowdowns in driving, and furthermore that other creatures besides large mammals surely benefited.

"Given the five- to nine-fold under-reporting of large animals involved in collisions with vehicles and the lack of systematic reporting of smaller mammals killed on roads," they concluded, "the positive impacts we report are likely to be just the tip of the iceberg of reduced deaths of wildlife on US roads and highways."

It’s not just wildlife benefitting here, either: As Cheryl Katz points out in National Geographic, an estimated 200 people per year die in the US in vehicle collisions involving wildlife.

While ungulates like deer and elk are the most common big roadkill in the three states evaluated (and the US in general), vehicle collisions can be a significant mortality factor for naturally scarcer large carnivores. That’s certainly true for mountain lions in California, particularly in the asphalt-heavy and traffic-snarled San Francisco Bay Area and Southern California, where isolated puma populations amid fragmented habitat find roads a tricky – and often lethal – obstacle to navigate. According to the Road Ecology Center’s report, as many as two vehicle-puma collisions per week are recorded in the state.

The study found that California experienced a decline in puma roadkill of 58% after the stay-at-home orders, underscoring the significance of traffic as a source of mortality for mountain lions here.

Mountain lions that eke out an existence in the shadow of big cities often fall victim to vehicle strikes. Image © National Park Service

Dr. T. Winston Vickers, director of the California Mountain Lion Project at the UC-Davis School of Veterinary Medicine, told The Mercury News in response to the study’s results, "For Southern California mountain lions, even one lion making it across a road instead of being killed can be very significant for populations like the ones in the Santa Monica or Santa Ana mountain ranges."

The Road Ecology Center report notes that traffic in all three states has increased as stay-at-home restrictions have eased, though, with COVID-19 infections currently spiking in much of the US, it’s not clear whether that upswing will continue, or at what magnitude. "The longer [a slowdown in traffic] lasts," Road Ecology Center co-director Fraser Shilling, one of the study’s authors, told National Geographic, "the more animals that would have died are not dying."

Many fewer cars tooling around are one way to cut down on wildlife road mortality. As the Road Ecology Center’s report observes, only moderate reductions in traffic may not always mean fewer WVC, as they could encourage more animals to try to cross still-dicey roads. Another way to reduce WVC, which is increasingly used all around the world, is the installation of wildlife-crossing structures and fencing to give animals, large and small, safe passage over or under roadways.

They’re certainly being pursued in California to both reduce road deaths and improve connectivity for pumas (and other species). In 2023, what will be the biggest critter-crossing bridge in the world – the 200-foot-long Liberty Canyon Wildlife Crossing over the Ventura Freeway in Greater Los Angeles – will hopefully make getting around for the famously hemmed-in mountain lions of the Santa Monica Mountains a bit less fraught.