Deer Population Management

Why do we manage deer?

Deer are an important part of Lake County's natural areas. Like other native species, they are beautiful and play a vital role in the ecosystem. But in some of our highest-quality preserves, deer numbers are so high that their populations are not in balance with the habitat. These large plant-eaters are consuming a great number of plants. Left unchecked, overbrowsing by deer damages habitat for other native plants and animals, including endangered species.

One of our key roles is to preserve a diversity of habitats for future generations. To maintain a balance between deer and other species, our policy is to manage deer numbers in the most humane and effective way possible.

Nature’s Delicate Balance

Deer populations increased dramatically as this region gradually became settled. Loss of natural predators and expansion of the edge habitat deer prefer have caused a major increase in their populations. Learn more »

Our winters are not severe enough to naturally reduce herds, and automobiles are now the only significant "predator" of deer in Lake County. People can compound the problem by illegally feeding wild deer, thereby supporting an even larger deer population.

Most female deer start to produce offspring when they're just two years old. They can breed for up to 12 years, some having twins each year. All these factors cause population growth, which greatly affects habitats.

How do we monitor the deer’s impact?

Our wildlife biologists have built "deer exclosures" at several preserves. Deer cannot get into these fenced-off areas but squirrels, groundhogs and other plant-eaters can. Outside these exclosures the deer roam free. We measure and compare the plants in both areas to assess the impact deer have on the habitat. Learn more »

Data collected since 1988 show that deer do pose a threat to the abundance and diversity of plants. Also, species favored by deer are less vigorous and produce fewer flowers outside the exclosures. To see an exclosure, visit Ryerson Conservation Area. Plan your visit for spring, when differences are most apparent.

Humane Removal

We keep up-to-date on developments in the field of deer management. This ensures that our program is conducted using the most effective, efficient and humane methods currently available. All methods used are approved by the Illinois Department of Natural Resources. Learn more »

Each winter, qualified sharpshooters lethally remove deer from several preserves under humane conditions. Work occurs at night after the preserves are closed, and all venison is donated to Lake County charities. This is the best management option currently available and is used by agencies nationwide.

Deer numbers are estimated each year with helicopter survey flights and pellet counts. Our population density goal is 15-30 deer per square mile, depending on habitat type. This goal is based on regional research recommendations. In preserves that are primarily forested, such as Old School and Wright Woods, we strive to maintain deer densities at 15 deer per square mile. In preserves that are comprised of more open habitats, such as savanna and prairie sites, we strive to maintain deer densities at 30 deer per square mile, because these plant communities have a longer growing season and can generally sustain larger numbers of deer. At these deer populations densities, we have a better chance of sustaining high quality habitats for other species.

It's all Connected

Our goal is to manage the preserves for overall health of the ecosystem. Giving preference to one species would be irresponsible. Deer are a valuable part of a balanced ecosystem, along with all other native plants and animals, but their populations must be monitored. Learn more »

Overabundant white-tailed deer populations can eliminate understory vegetation, directly impacting the plant community. Reduced understory also decreases cover that serves as nesting locations for ground-nesting birds, cover for woodland frogs and salamanders, and sheltered resting sites for other wildlife species.

Ultimately, deer can reduce vegetation so much that they no longer have adequate food to sustain their own population. When this occurs many deer die from starvation.

Overabundant deer populations also increase the risk for disease transmission (e.g. Chronic Wasting Disease), parasite transmission (e.g. deer ticks which can carry the bacteria that causes Lyme disease), and deer-vehicle accidents.

At the preserves where deer are currently managed, research shows the overall health of the deer herds and plant communities have improved. Areas that were once almost devoid of vegetation now flourish with a diversity of flowering plants in the forest understory.