Collisions with deer spike every November. One surprising factor? Daylight saving time

More drivers collide with deer on Wisconsin roads in the early weeks of November than at any other time of the year.

The reason for our annual post-Halloween headache may surprise you: it's the end of daylight saving time.

That's right, this controversial clock reset on the first Sunday in November likely contributes to the annual spike in deer crashes around this time of year. That's because setting the clock back by an hour almost perfectly realigns rush hour with dusk, when deer are particularly active.

To make matters worse, this change occurs in the middle of breeding season for white-tailed deer.

This creates a dangerous environment for drivers and deer alike. On average, 16,000 deer collisions happen in Wisconsin each year. And more drivers and passengers are injured in November than in any other month.

In November 2022, an average of 100 drivers collided with deer each day. That's almost three times the typical number of daily crashes during the rest of the year.

Timothy Van Deelen is a professor at the University of Wisconsin-Madison in the Department of Forest and Wildlife Ecology. He said the breeding season increases the likelihood of human-deer interactions for three or four weeks each fall.

"The male deer is almost a different animal during the breeding season, behaviorally," Van Deelen said. "Bucks will dramatically extend their home range, and mature bucks are moving through their big home range trying to find does who are receptive to being bred."

Wisconsin sees a second, smaller peak in deer crashes around the beginning of June each year. This too aligns with deer behavior, according to Van Deelen.

"About the time that the female deer are establishing their fawning ranges in early May or late April, they're also kicking last year's fawns out," said Van Deelen.

That means male fawns are striking out on their own for the first time, sometimes through unfamiliar territory.

What does this have to do with daylight saving time?

The return to standard time in November could also be responsible for some deer collisions. Winding the clock back by an hour brings rush hour in alignment with dusk, which is when deer tend to be most active.

Using data from the state Department of Transportation, the Milwaukee Journal Sentinel mapped deer collisions by month, week, day, and hour. Our analysis found that Wisconsin deer crashes consistently peak in the week immediately following the end of daylight saving time, when high-traffic hours align with sunset.

That tracks with a study from a team of researchers at the University of Washington in 2022. Laura Prugh and Calum Cunningham led the team that analyzed deer crash data from 23 states. They found that ending the annual "fall back" could prevent as many as 33 human deaths and $1.19 billion in property damage due to deer crashes across the U.S. each year.

The researchers in Washington didn’t include Wisconsin in their analysis, but the state's deer crash data shows a similar pattern.

Wisconsin Department of Natural Resources deer program specialist Jeff Pritzl said he had not thought about the impact of daylight saving time before but said it makes "perfect sense."

He pointed out that the U.S. used to end daylight saving time on the last Sunday in October, until the federal Energy Policy Act changed that in 2005. Since then, we’ve set our clocks back on the first Sunday in November.

Pritzl said this has been a problem for our state’s ungulate residents. 

“[The end of daylight saving time] is now smack dab in the middle of the deer breeding season, when they are most active and moving around,” Pritzl said in an email.

Here's what you can do to prevent a deer crash this fall

Since the beginning of 2020, more than 1,600 people have been injured as a result of a deer crash in Wisconsin, and 27 people have died. Last year, five people died as a result of deer collisions.

The researchers in Washington proposed permanently switching to daylight saving time to prevent deaths and property damage.

But with a little knowledge about deer behavior, Wisconsin drivers can stay as safe as possible. 

Primarily, drivers should avoid the roads after dark as much as they can, according to Laura Prugh, co-author of the Washington study. If you must drive, the state Department of Transportation recommends slowing down, avoiding distractions, and scanning the sides of the road carefully.

"[Deer] quite frequently are traveling together in small kin groups," Van Deelen said. If you see one on the road, slowing down is the only safe strategy, he added. "They're not very moved by a horn or a whistle or anything, so you can't mitigate a deer collision by making noise."

Check out previous years' deer crash data

For the last six years, the Milwaukee Journal Sentinel has requested data from the state Department of Transportation for each deer crash in Wisconsin. In previous years, we have reported on the rising costs of deer collisions, the increased danger motorcyclists face because of deer, and how the COVID-19 pandemic changed driving habits, but did not reduce deer crashes. 

Read our previous stories:

• 2022: Deer crashes, supply chain in Wisconsin causing drivers to pay more to keep their vehicles
• 2021: It's deer crash season in Wisconsin. Here's where you're most likely to hit a deer.
• 2020: Deer are running all over in Wisconsin right now and motorists are crashing into them across the state
• 2019: It's deer vs. car season in Wisconsin. These are the riskiest times and places.

Andrew Hahn is the newsroom developer for the Milwaukee Journal Sentinel. Reach him at ahahn@gannett.com or on X at @ndrewhahn.

Editor’s note: This story was republished Feb. 13, 2024, to make it free for all readers.