Rutting deer are wreaking havoc on Minnesota roadways, study finds

An unseen menace is stalking Minnesota’s roadways. It tends to strike just before dawn or just after sunset, when visibility is low. It leaps from the shadows with little regard for its own safety, killing several Minnesota victims every year, wounding hundreds more, and causing untold millions in property damage.

We’re talking about deer, of course.

Early November is peak season for deer-vehicle collisions in Minnesota, according to a comprehensive dataset compiled late last year by researchers at the University of Washington. 

The sheer numbers are staggering: A Minnesota motorist’s odds of striking a deer in the first week of November are roughly 10 times higher than in midsummer.

It’s a temporal pattern that holds true for most of the eastern U.S., where whitetail deer are plentiful, the researchers explain. 

The primary cause of this is that deer are in rut, meaning they’re preoccupied with finding a mate and have grown reckless as a result. That carelessness makes them easier targets for hunters, which is one reason why whitetail season typically opens the first week in November.

But there’s another factor at play too, and it should attract the attention of policymakers: The switch from daylight saving to standard time. This pushes traffic peaks back an hour relative to the solar time. Deer that have grown accustomed to avoiding roadways at certain times of day suddenly find them congested an hour later than usual. Human grogginess also plays a role in the increased collisions.

The University of Washington researchers found that the accidents peaked shortly before sunrise in the mornings, and shortly after sunsets in the evenings. Other research has shown that deer are equally active before and after sunrise or sunset, suggesting that human error — especially difficulty seeing things in low light conditions — is largely to blame for this pattern.

Deer-vehicle collisions tend to increase the further north you go, owing to the increased length of nighttime hours during the winter. Collisions are also 35% more frequent at the eastern edge of time zones than at the western edge, owing to relatively earlier sunsets in the east. And across the board, collisions are more likely to happen in the evening hours than in the morning.

From a policy standpoint, the authors find that enacting a permanent daylight saving time could reduce the annual number of deer collisions in the U.S. by about 36,000, preventing 2,000 injuries, several dozens of deaths, and roughly $1 billion in property damage.

Switching to permanent standard time, on the other hand, would have the opposite effect: The darker evenings would mean more collisions, not fewer.

The authors note that introducing more wolves would also likely reduce collisions between vehicles and deer. One prior study conducted in Wisconsin, for instance, found that the reintroduction of wolves in a county reduces deer-vehicle collisions by an astonishing 24%, yielding an overall economic benefit 63 times greater than the cost of increased wolf predation on livestock.