Jerry Corcoran
Resource Manager
The white-tailed deer is a common sighting for Property Owners and guests in and around Woodhaven. I believe the white-tail deer is actually a common sighting throughout the state wherever one travels. In 2019, deer numbers throughout Illinois were estimated at 670,000 with an estimated population in the United States of 30 million! The white-tail deer is abundant. What happens when there are too many deer on the landscape?
When deer populations become too high, natural landscapes can be negatively impacted. Deer can over browse the existing plants and young trees to the point where the overall ecological health of a given area declines. Seedling trees are browsed off thus reducing the number of understory tree survival. In a healthy ecosystem, these understory trees over time replace older, declining and dead trees. Reduction in the understory trees changes the plant structure that normally makes up the plant community. Native plants are replaced by invasive species such as garlic mustard and oriental bittersweet. These two species further degrade the existing plant community as they out compete them.
In addition to natural areas, landscape plantings around homes in communities become targets for deer. Deer browse on all species of plants, trees and shrubs granted they are species they find palatable. Landscape plantings can be decimated by deer at certain times of the year. Homeowner’s vegetable gardens are often targeted by deer when unprotected. Trees, especially young ones, are browsed and during the early fall bucks rub the trees to remove the shedding velvet from their newly grown antlers. Trees up to 6 inches in diameter can be stripped of their bark thus causing the tree to weaken and/or die.
Tick borne diseases become more prevalent with increased deer numbers. Lyme disease has been increasing in the state of Illinois. Some of the research indicates that high numbers of deer in an area increases the incidence of Lyme disease.
Deer vehicle collisions increase when deer populations are high. According to State Farm, U.S. drivers on average have a 1 in 116 chance of colliding with an animal. The large majority of these collisions are with deer. There were 1.5 million animal collision insurance claims in the U.S. between July 2019 and June 2020. In Illinois, the chance of hitting an animal is 1 in 148. This leads to deaths, injuries, and vehicle repair expenses.
Too many deer can be detrimental to the health of the deer population in an area. As deer numbers increase, there is an increased pressure on the food resources to sustain healthy animals. All environments in which deer live have what is called a “carrying capacity.” Carrying capacity for deer, simply put, is the number of animals that a given area of land can support. For the white-tailed deer, a healthy number of animals on average is 20 deer per square mile. Exceeding the carrying capacity can lead to malnutrition in animals.
Transmission of disease increases in an area when deer numbers are high. The disease that continues to increase in the Midwest is Chronic Wasting Disease (CWD). States have been dealing with this disease affecting the deer populations for a number of years with limited success. There is no cure for the disease at this time. When deer contract CWD, it is always fatal. This disease was first identified in Colorado and Wyoming in the 1960s and 70s. Since then it has spread to affect animals across the U.S. in 24 states as well as 3 provinces in Canada. Where the disease is established, it is increasing in prevalence.
In Illinois, CWD was first found in 2002 in Boone County. This is in the northern part of the state near Wisconsin. The disease has since spread to infect deer in 18 counties within the state as far south as Livingston County. It has also spread to Lake, Cook and DuPage counties in the northeast part of the state. Most recently, a deer was sampled from Lee county that tested positive for the disease.
Deer generally have a “home range,” where they spend the majority of their time feeding, resting, breeding and raising young. The size of the home range can vary depending on the quality of habitat but on average is around 1 square mile. During the year, deer, often males, tend to move out away from their home range. Deer that move out will generally move back to that home range in a short period of time. It is during these excursions that deer can become infected with CWD, thus spreading the disease to previously uninfected areas.
States, where CWD is occurring, are managing the disease by reducing deer populations to slow the spread. White-tail deer numbers are reduced during the designated hunting seasons each fall and early winter. The deer harvest across the state in 2020/21 was 162,500 animals. This number is up from 2019/21 which was 153,000. That may seem like a lot of deer, but compare it to the estimated population of deer across the state in 2019 which was 670,000.
Following the state hunting seasons, the Illinois Department of Natural Resources (IDNR) staff target deer populations in areas of high disease prevalence. In the late winter, IDNR staff attempt to reduce deer populations by enlisting sharpshooters to cull out animals in small designated areas within the counties where the disease has been identified. There were a total of 1,107 deer removed from these areas in 2020, of which 42 tested positive for CWD. Samples are also collected during the designated hunting season from animals harvested in the counties with CWD to continue monitoring the population.
The take home message in the information provided in this article is that deer populations need management to maintain the health of the herd, ecosystems and humans. Since natural predators of deer have been eliminated from most of their range, the main predator today is hunters. Hunting is the main way that the deer population is being managed. Without hunting, deer populations would go unchecked leading to more widespread disease and ecosystem degradation.