The surprising science behind why daylight saving time is good for wildlife

The surprising science behind why daylight saving time is good for wildlife

By Jackie Flynn Mogensen edited by Claire Cameron

Most Americans have a love-hate relationship with the change to Daylight Saving Time (DST). On the one hand, we lose an hour of sleep, which can disrupt circadian rhythms, leaving us groggy and possibly even leading to deeper health problems. On the other hand, it also means longer, sunnier evenings and more days for outdoor activities. But what about other animals? Surprisingly, science suggests that daylight saving time could be beneficial for creatures that encounter humans, and especially those that might encounter our cars.

In the United States alone, drivers can collide with deer up to more than 1 million times a year, according to estimates compiled by the Federal Highway Administration, and other large animals, typically moose, elk and other ungulates, are also often affected. These accidents frequently kill animals and lead to hundreds of human deaths.

The risk of animals being killed on the road depends on several factors, including the number of vehicles on the road, the number of animals on the road and the behavior of animals and human drivers, says Tom Langen, a biology professor at Clarkson University who studies animal-vehicle collisions. Daylight saving time can, however, minimize these collisions.

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Human-animal accidents usually happen on Fridays because people leave town for the weekend; during full moons, as deer are more likely to be on the move; during the fall mating season of deer in North America; and at dusk.

“Animals become active just after dusk and start moving around, including crossing roads or grazing along roadsides, and that’s when they get hit by vehicles,” says Langen.

Turning back the clocks in the fall — moving peak nighttime travel hours closer to dusk or after sunset — also increases the chances of cars hitting animals. In a 2021 analysis of more than 35,000 vehicle-deer collisions in New York state, Langen and a co-author concluded that the return to standard time from DST contributed to “much higher” crash rates, with the largest increases on workdays.

A 2022 study by University of Washington researchers concluded that permanently switching to daylight saving time could save about 33 human lives per year, prevent about 36,000 deer deaths from car crashes, and reduce some of the $1 billion in costs associated with these collisions. These costs include property damage and medical expenses.

“We were surprised to find that the increase in collisions that we see when it is darker in the evening at standard time is not offset by a reduction in collisions in the morning,” says Laura Prugh, lead author of the 2022 paper and professor of quantitative wildlife science at the University of Washington.

In fact, the rate of deer collisions was 14 times higher just after dark than before sunset, leading to a “net increase” in deer collisions during normal months, she said.

Moving the clocks forward in spring means darker morning commutes, but little additional risk to deer and other ungulates. Part of the reason is that deer tend to be less active in the spring, Langen said. But it is also because evening trips will mainly take place before dusk.

In other words, from a human perspective, DST is a matter of luck, depending on who you ask. (And polls indicate that opinions on this are mixed.) But for animals like deer, moving to permanent daylight saving time in North America would almost certainly reduce road deaths, Langen says.

And it’s not just deer and ungulates that are in danger: Other mammals, including raccoons, skunks and foxes, are also active at dusk, Langen says. In Australia, research shows that even koalas could benefit from the move to permanent daylight saving time.

Ultimately, Langen recommends that drivers stay safe by being aware of peak collision periods throughout the year and keep in mind that animals often cross the road in groups. Staying alert at dusk is also a good practice, Prugh adds.

“It’s important for drivers to be aware that animal encounters can happen at any time, but there are certain times when you are particularly at risk,” says Langen.

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