Counting Deer at Pea Ridge National Military Park, 2005–2023

White-tailed deer are among the most familiar animals at Pea Ridge National Military Park in Arkansas. It is hard to believe they were nearly wiped out in the early 1900s by overhunting and forest clearing. Hunting regulations — and the removal of most of their natural predators — have since led to unprecedented growth in deer numbers. Without predators, deer can become overpopulated and die of disease and starvation.

Scientists from the National Park Service's Heartland Inventory and Monitoring Network track the park's deer to see how their numbers change over time.

White-tailed deer at Pea Ridge National Military Park (NPS).

Why count deer?

A central goal at Pea Ridge is to restore the oak savanna and oak forest that covered the land at the time of its Civil War battle. Deer love to browse tree saplings and other native plants, and when there are too many of them:

• overbrowsing can undermine the restoration and favor invasive, non-native plants;
• deer spread ticks that can carry disease to other animals and to people, and those diseases become harder to manage;
• deer–vehicle collisions increase.

Monitoring gives park staff the information to make decisions that protect the deer, other wildlife, the park's habitats and people.

How the count works

Monitoring began in 2005. Each winter, during a four-week window between January and mid-March, the team drives slowly at night around the park's main tour road — a 10-kilometer loop — shining bright spotlights to count the deer and map where they are.

White-tailed deer at Pea Ridge (NPS).

What 19 years of counts show

The team has seen rapid declines and recoveries. The population fell to a low of about 15 deer per square kilometer in 2007, after a two-year outbreak of hemorrhagic disease, and reached about 63 per square kilometer in 2023.

Despite that early die-off, the herd grew moderately overall — an average of 3.2% a year. An analysis of hunting and monitoring data suggests that something other than hunting is driving the year-to-year changes. The team will keep counting to help the park manage deer and to understand what shapes their numbers.

Deer locations along the tour road in 2023, with the area visible from the survey vehicle (NPS).

Why do deer eyes glow?

A white-tailed deer's eyeshine (NPS).

Shine a light at a deer at night and its eyes glow. Many animals share this eyeshine — dogs, cats, cattle and horses, and even some reptiles, amphibians, fish, birds and insects. It comes from a reflective layer behind the retina called the tapetum lucidum, Latin for "tapestry of light" or "shining layer," which helps them see in the dark.

Deer can be active by day or night, but they are crepuscular — most active at dawn and dusk. The reflective layer, together with large pupils, helps them get around in dim light.

That is exactly what the survey uses. In the dark, a deer's pupils are wide open; when the spotlight hits them, the deer freeze until their eyes adjust — the origin of the saying "like a deer in headlights," for someone too startled or scared to move. The light does the deer no harm, and it lets the team count them.

Sources

• National Park Service, Heartland Inventory and Monitoring Network: "Deer Monitoring at Pea Ridge National Military Park in Arkansas, 2023."