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Opinion >  Column

Fear the deer: Crash data illuminates America’s deadliest animal

Jan. 23, 2023 Updated Mon., Jan. 23, 2023 at 9:41 p.m.

 (Washington Post)
(Washington Post)

Behold the deer, the deadliest beast in North America.

Deer are responsible for the deaths of about 440 of the estimated 458 Americans killed in physical confrontations with wildlife in an average year, according to Utah State University biologist Mike Conover, employing some educated guesswork in the latest edition of “Human-Wildlife Interactions.”

Those deer-inflicted fatalities are not, so far as we know, caused by deer-on-human predation. They’re the unfortunate result of more than 2 million people a year plowing into deer with their sedans and SUVs, usually on a two-lane road, often at high speeds.

You might wonder: Where and when am I most likely to hit a deer? And how can I avoid it?

To shed light on this herbivorous hazard, we turned, of course, to data. Specifically, we analyzed more than 1 million animal-vehicle collisions compiled by Calumn Cunningham, Laura Prugh and their colleagues at the University of Washington for a recent paper published in Current Biology. They estimate deer were involved in more than 90% of the collisions, which occurred in 23 states between 1994 and 2021.

With a few exceptions, the data show deer are at their most dangerous in November. Indeed, the deer threat peaks just before Thanksgiving – typically Nov. 7 through 14 – when you’re about three times more likely to hit a deer than at any other time of year.

Experienced deer hunters can probably guess why driving in November can turn into Russian roulette on certain highways and byways: In much of the country, that’s rutting season. And during the rut, deer focus on procreation, not self-preservation. Marianne Gauldin of the Alabama Wildlife and Freshwater Fisheries Division compares rutting bucks to teenage boys.

“They are hyper-focused on the opportunity to breed, and they therefore lose some of their wits,” Gauldin said. “They are full-tilt looking for does, chasing does and running after does for the opportunity to breed. And they are doing this with tunnel vision … literally running across the road.”

Does share similar distractions. They’re either in estrus – hormonally receptive to sex and looking to breed – or fleeing hot-and-bothered bucks until their cycles catch up.

Collisions occur more often in states with the most white-tailed deer – which experts say tend to have a shorter, sharper rut than the western mule deer – and in states with long stretches of busy rural roads. Separate insurance claim data from State Farm, which is widely cited in academic research, shows a driver out minding her own business on the wending, bending roads of West Virginia had a 1 in 35 chance of hitting an animal between June 2021 and June 2022, making the Mountain State easily the most dangerous in terms of deer-car collisions. Montana and Michigan were next. D.C. drivers, by contrast, had only a 1 in 907 chance of stopping a buck while driving down Pennsylvania Avenue, or anywhere else.

Fun fact: Deer are responsible for at least 69 percent of animal-related accident claims, according to State Farm. Another 12% of claims involve unidentified animals, many of which could be deer that bounded off before the driver got a good look at them or were mangled beyond recognition in the crash.

The third-most-dangerous animals on the road are undifferentiated rodents, which are cited in 5% of all animal-related accident claims. However, State Farm spokesperson Dave Phillips noted that many of the drivers never make contact with said rodent: The vast majority of those accidents occur when motorists swerve to avoid a suicidal squirrel or moseying marmot.

Our more calendar-conscious readers will note that peak deer-crash season coincides with another big moment in November: the first week of daylight saving time, which begins the first Sunday of the month. And the University of Washington team has found that the two events are not unrelated.

To understand why, we need to spelunk deeper into their data, which breaks new ground by including the exact location, date and hour of all these deer disasters. When we glance at a chart of accidents that includes time of day and time of year, one fact strikes us right between the headlights: Evening, the twilight of each day – especially in November! – is the hour of the Götterdeermmerung.

Conveniently for us, the University of Washington scholars used accident coordinates and some basic weather math to calculate exactly when the sun would have risen or set at each location. It turns out that deer danger skyrockets about 30 minutes after sunset and remains extraordinarily elevated for almost half an hour.

Those with deer-behavior expertise say drivers should be on high alert as darkness falls in autumn – especially when careening through the deer’s favorite transitional habitats, the forest-edge ecosystem created by roads and other developments. But they urge us to take a lesson from the thousands of people who land in hospitals and body shops each year after attempting to avoid a turtle or chipmunk: If you do see a deer, don’t swerve.

“Slow down as much as you can, obviously, coming up to it,” said Karlin Gill of the National Deer Association, a hunting and conservation organization. “But if it’s unavoidable and you’re going to hit the deer, don’t try and swerve out of the way. That can cause an even worse car wreck, and you still might hit the deer regardless.”

Deer crashes also rise in the morning, about 30 minutes before sunrise, but the number is significantly lower than after sunset. To understand why, we need to dig deeper into both deer and human activity patterns.

Biologist after biologist told us deer are crepuscular, meaning they’re most active at dawn and dusk. When Texas A&M University wildlife scientist Stephen Webb and his colleagues fitted GPS trackers onto white-tailed deer in Oklahoma, they found deer movement peaks at both sunrise and sunset.

“Deer, unlike humans, don’t lay down for eight hours at night and then get up and move throughout the day,” said Gill, who, as a hunter, closely examines deer behavior. “They actually go through a cycle where they’ll lay down, bed, get up, eat, lay down, bed, get up, eat, and they’ll do this throughout a 24-hour period.”

But if deer are equally active at dawn and dusk, why are they so much more likely to be hit in the evening? To untangle that one, we need to examine another somewhat crepuscular species: the American commuter. Our commutes also peak in the morning and evening, but we’re much more likely to be driving at dusk than we are at dawn, and we stay on the roads even as darkness falls and the deer start moving – often squarely into our headlights.

It’s a matter of visibility. Deer are just as active two hours before dusk as they are two hours after, yet we’re about 14 times more likely to hit a deer after sundown than we are before.

And, as Cunningham notes, right at the peak of the whitetail rut, we throw another variable into the stew: We end daylight saving time. Suddenly, as far as the deer are concerned, our 6 p.m. commute happens an hour later. Millions of drivers find themselves contending with lower visibility just as sex hormones flood the local deer population.

“It’s like one of the grandest-scale natural experiments that we can come up with, where humans impose these very arbitrary and abrupt changes on the wildlife,” Cunningham told us from his native Tasmania (he’s at the University of Washington as a Fulbright fellow).

People living on the far eastern side of a time zone are about 1.35 times as likely to hit a deer as folks on the far western edge, since folks in the east are more likely to be driving home in the dark. Similarly, folks in Northern states, where days are short and darkness rules the winter, are 1.86 times more likely to hit a deer than their friends in America’s sunny South.

Taking these effects into account, the University of Washington team estimates that “falling back” causes a 16% jump in deer carnage in the weeks after the shift. It’s possible that adopting permanent daylight saving time would thus save the lives of more than 36,000 deer and 33 humans each year.

On the down side, chronobiologist Eva Winnebeck of the University of Surrey argues that any gains might be offset by an increase in deaths spurred by the chronic drowsiness that would inevitably set in if our solar-powered circadian rhythms were forced to endure a never-ending disconnect between the sun and clocks set permanently to daylight saving time.

Here at the Department of Data, we’ve found a strong connection between happiness and the great outdoors. So we’re partial to any move that would give us more daylight hours to get out after work and fish, run or dominate the competitive wood-chopping circuit, circadian rhythms be darned.

Andrew Van Dam writes the Department of Data column each week for the Washington Post. He has covered economics and wrangled data and graphics for the Post and the Wall Street Journal.

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