Cars hit more deer in the week after daylight saving time ends

Permanent daylight saving time could save tens of thousands of deer and dozens of people

A car's headlights reveal a deer crossing a two-lane road, with deer crossing signs in the background.

Turning the clocks back after daylight saving time means more people drive in the dark. They are also more likely to collide with deer. Scientists estimate keeping daylight saving time could save dozens of human lives.

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People pay deerly for the switch from daylight saving time.

Each November most Americans turn their clocks back one hour. This marks the end of daylight saving time and a return to standard time.

Scientists now report that this autumn time change corresponds to an average 16 percent increase in car collisions with deer. They shared their finding November 2 in Current Biology. Keeping daylight saving time all year could save nearly 37,000 deer per year — as well as 33 human lives, the researchers estimate.

In a typical year, drivers hit more than 2 million deer. That’s about 7 percent of all car crashes in the United States. Wildlife biologist Laura Prugh and her colleagues wanted to see if changing from daylight saving to standard time and back affected the number of car crashes. These researchers work at the University of Washington in Seattle.

The team collected car crash data from 23 states. These states kept track of whether a crash involved an animal and at what time the crash occurred. Then the researchers compared those numbers to an hourly count of cars on the road between 2013 and 2019. They focused on the weeks before and after the switch to daylight saving time in spring and then back to standard time in the fall.

Turning the clock forward in spring had little effect. But almost 10 percent of yearly car collisions with deer took place around the autumn fall back period, on average. Losing an hour means the sun sets earlier in the evening. This means more people drive after dark.

The problem was bigger on the East Coast. “You see [a] really steep spike in the fall,” says Prugh. “In the western states, you also see an increase, but it’s not nearly as sharp of an increase.” On the East Coast, the autumn switch falls in the middle of mating season for white-tailed deer. Not only are more drivers active after dark, but the deer are too. They’re wandering around looking for love. Concludes Prugh: “The timing could not be worse.”

Ending the clock change wouldn’t completely wipe out the spike in crashes. Mating season would still play a big role, regardless of what time the sun sets. But keeping daylight saving time all year would decrease collisions between humans and deer by about 2 percent, the scientists estimate. This could save dozens of human lives, thousands of human injuries and tens of thousands of deer fatalities every year. It’s a good reason for us all to see the light.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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