In the mid-1920s, William R. Angell brought nine white-tailed deer to North Manitou Island for hunting; by the early 1980s, the herd was estimated at 2,000

Imagine nine deer stepping off a boat onto a quiet island in Lake Michigan. That’s how it began. Almost a century later, scientists are still trying to figure out what those six deer did to the island. A 2021 study on North and South Manitou islands, published by researchers including Jean Tsao of Michigan State University in the journal Ticks and Tick-borne Diseases, used the islands as a natural experiment to understand how the presence or absence of deer affects tick populations and the pathogens they carry. Their work helps explain how one hunting idea reshaped the island's ecosystem.

A rich man's hunting dream

North Manitou Island is off the coast of Michigan, part of the present-day Sleeping Bear Dunes National Lakeshore. In the 1920s, the island was privately owned and operated by the Manitou Island Association, a group of landowners who wanted to turn the island into an exclusive playground for wealthy sportsmen. There was only one problem: there was no big game on the island. In the mid-1920s, nine white-tailed deer were brought to North Manitou under the direction of William R. Angell. The aim was simple: let the deer multiply, and charge hunters for the experience. It worked, and the herd grew far beyond expectations.

From nine deer to a hunting empire

The first organized hunt was in 1937 when 18 deer were taken that season. Edgar McKee, who operated the island from 1937 to 1942, once described hunting as being divided into two three-day sessions a week, beginning about November 1. Historical accounts of the era describe hunters paying around $150 for a package that included the boat ride, hotel and meals, a trained guide and a guaranteed deer, though the exact figure is difficult to verify against a single authoritative record. The island was divided into ten sections, which guides had scouted in advance, and only ten hunters were allowed out at a time, always with a guide.

For decades, the island functioned as an exclusive hunting retreat, similar to private clubs popular among wealthy sportsmen in the late 1800s. Company executives and their guests came for a few days of organized hunting, with almost none of the usual hardship. Guides tracked, prepared, and delivered the deer, and the system remained in place for more than 50 years.

When there are no predators

Deer breed fast when the conditions are favorable, and those were the conditions on North Manitou. There were no predators such as wolves or coyotes; sufficient food and proper management of the deer by the island's owners let the herd expand rapidly from its original nine founders. By the early 1980s, estimates of the population reached approximately 2,000 deer.

As that herd grew over the decades, it began eating nearly any available vegetation. The remaining plants were those deer tended to avoid, such as American beech, which now grows in unusual abundance on the island. This pattern is consistent with studies of browse damage in other areas of the Great Lakes region. In a 2018 study published in PLOS ONE led by Stephanie Patton and colleagues at the University of Minnesota, researchers found that white-tailed deer overbrowsing has measurable effects on forest regrowth in Michigan, Minnesota, and Wisconsin, making some tree species less common and others dominant.

A forest with a haircut

Walk through North Manitou today, and you can see where the deer have been eating. Visitors and researchers report a browse line about five to six feet up, where the leaves and branches are left untouched, and below which there is almost nothing soft or tasty left. Contrast that with neighboring South Manitou, which never had deer. South Manitou still has a thick understory of shrubs, ferns, and vines close to the ground, while North Manitou looks unusually trim and manicured after decades of steady browsing pressure.

The island today

The National Park Service took over North Manitou in 1984 and has conducted limited deer hunts since then, hoping to reduce the herd's impact on the island's plants. Today's hunters are on their own tracking deer without a guide, unlike the guided hunts of the 1930s. The deer on the island changed life for smaller creatures, too. The 2021 tick study found that North Manitou's deer herd helps maintain the local tick population, serving as the large-bodied host adult ticks need to feed and reproduce, though deer themselves are a poor reservoir for the bacteria that cause Lyme disease. On deer-free South Manitou, the researchers found that coyotes and chipmunks fill those roles instead: coyotes as an alternative large host for adult ticks, and chipmunks among the small-mammal reservoirs that can sustain the Lyme bacterium. It's a reminder of how a single introduced species can reshape an entire food web, down to the insects.

What began as a plan to make hunting easier became a century-long lesson in unintended consequences. Nine deer with no predators and unlimited food grew into a herd of roughly 2,000 and changed the forests of an island. It is a small story with a larger lesson: ecosystems can change quickly when humans alter the balance, even unintentionally.