Pakula's Research Featured in Science

Deer running toward an oncoming golf cart with experimental headlights show widely variable responses depending on individual personalities and experiences. Even so, they’re less likely to notice and react to LED headlights compared with halogens—leading cart drivers to slam on the brakes to prevent head-on collisions with deer who ignore the danger. -- Pakula et al., Applied Animal Behaviour Science 2025

Will your car hit that deer? Depends on your headlight bulbs -- and the deer's personality

Halogen bulbs are more reliably catch deer's attention, but whether the animals flee or freeze comes down to the individual temperament

30 May 2025, By Christa Lesté-Lasserre

When driving down a dark road at night, few sights are scarier than suddenly finding a deer’s eyes reflecting back at you. Paradoxical though it may seem, this quick “deer-in-the-headlights” response is actually a good thing because it means the deer has spotted you and registered you as a threat. But if the animal freezes for too long, it can spell doom for both it and your car.

Now, researchers report that two different factors determine whether these split-second moments end with a crash. For one, not all cars’ headlight bulbs do an equally good job at catching deer’s attention, with halogen headlamps more likely to trigger a deer-in-the-headlights glance than LED bulbs.

Don’t rush to switch out your headlights, though. The study, published earlier this month in Applied Animal Behaviour Science, also finds that a deer’s personality and life experience may have far more to do with how it responds to the danger your car poses—and may ultimately shape whether the animal freezes up in the road or bolts away to safety.

“It’s a really exciting area of research,” says John Orrock, a behavioral ecologist at the University of Wisconsin–Madison who was not involved in the study. “What’s key here is that it’s not whether you’ve got a deer in the headlights—and not so much even which headlights—but which deer you have in the headlights.”

For study co-author Travis DeVault, a wildlife biologist at the University of Georgia (UGA), the research is at least partially personal. Once, while driving in an Ohio forest, he hit a deer—and the animal’s eyes seem to have never gotten in his headlights at all. Over the past few years, he and other researchers at the university’s Whitehall Deer Research Facility, which houses dozens of captive white-tailed deer (Odocoileus virginianus), have been studying how the animals respond to various kinds of light.

In the new study, DeVault and colleagues—including Ph.D. student Carson Pakula, whose grandfather and uncle had both struck deer in rural Michigan—explored whether newer LED headlight bulbs might be messing with deer’s vision. LEDs have bluer wavelengths than traditional reddish orange halogen bulbs, and a deer’s eyes are more sensitive to these short wavelengths. That could make them more likely to get “overwhelmed” by the LED light so much that they freeze up completely, sort of like when we get stunned by flash photography.

To test whether deer were less overwhelmed by halogens, the researchers outfitted a 2021 Yamaha golf cart with various sets of lights, including halogen and LED headlights, that could create different lighting setups. They then released 23 female deer, one by one, toward the cart as it traveled about 28 kilometers per hour—to give a safe but realistic stopping time—down a grassy pathway. To mimic head-on collision situations, the cart’s driver braked when a deer either stood about 5 meters away or started to run away. The team tested each animal in each lighting condition randomly, on different days.

Deer were 39% more likely to act “alert”—meaning they picked up their heads and looked at the oncoming headlights in a split second of recognizing danger—when the lights were high-beam halogens compared with LEDs, whether high or low, the team found. Those that didn’t alert never glanced up at the headlights at all, ignoring the imminent threat completely.

But that halogen edge didn’t last, as alert deer then took matters into their own hooves. Some bolted; others froze long term in that infamous and deadly deer-in-headlights stance. Some choices seemed random; others appeared to follow personal patterns of usually fleeing or freezing, as if driven by their unique personalities—bold, shy, or cautious, for example—and possibly past experiences with danger, the researchers say.

“It could be that by the time you’re in imminent collision scenario, you’re kind of at the mercy of the deer,” DeVault says.

Orrock applauds the researchers’ “creativity,” though he questions whether the experiment’s narrow corridor trapped deer that would have otherwise run off. UGA behavioral ecologist Gino D’Angelo, who was not involved with the work, counters that a highway after dark is effectively a corridor all its own. “Try standing alongside a highway at night,” he says. “Even I have felt caught in the headlights.”

In any case, special lighting probably can’t solve the collision problem on its own, Orrock says. He advises that people drive less often and more slowly at night, while using high beams whenever possible and remaining vigilant for deer—especially a second or third deer following the first one you see. Should a deer appear, brake and don’t swerve, as that can lead to collisions with objects on the side of the road or oncoming vehicles, DeVault warns. “A lot of the outcome,” Orrock adds, “is up to the person—not the deer.”

Check out the full article here!