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PUBLICATIONS Inside Illinois Vol. 24, No. 1, July 1, 2004

Deer dilemma
Increase in deer population causes concern at Allerton

By Sharita Forrest, Assistant Editor
217-244-1072; slforres@illinois.edu

Photo by Bill Wiegand
Tasty treat? A 10-foot fence, which was constructed in 1987 around the meadows, conference center and formal gardens, has done little to deter deer from eating and damaging cultivated areas at Robert Allerton Park, Monticello. More worrisome to biologists is the adverse impact the herd is having on the natural areas.

Every year, thousands of visitors travel to Monticello to enjoy the pastoral splendor of the gardens, meadow and forest of Robert Allerton Park.

However, high numbers of another type of guest – the white-tailed deer – are becoming increasingly problematic in the park and adjacent 4-H camp. Like elsewhere in Illinois and in other states such as Wisconsin, the population of white-tailed deer at Allerton has grown dramatically, raising concerns about the impact the deer herd may be having on the park’s natural areas and the herd’s potential for transmitting diseases to humans and domestic animals.

Since 1981, UI biologists have conducted annual counts of deer in and around Allerton, which they perform by helicopter during the winter months when snow cover and the absence of foliage provide an ideal backdrop for spotting deer. During this year’s count, which was conducted in February under conditions deemed nearly ideal, biologists estimated that there were more than 730 deer in the park and the 5,700 acres around it, a significant increase from the 550 deer they estimated were in the area during the 2003 count.

Over the course of 2004, biologists estimate that the area’s deer population will likely swell by another 350 deer as does give birth.

While biologists believe that the optimal deer population in a natural area such as Allerton is 20 or fewer deer per square mile, Allerton has an estimated 163 deer per square mile browsing its gardens, forest and meadow.

Deer herds throughout the United States have increased exponentially in recent decades, although around 1900, deer were “functionally gone from Illinois,” said Dick Warner, a professor of natural resources and environmental sciences and one of the UI biologists studying the issue. Restrictions on hunting and programs for trapping and relocating deer helped the deer population rebound beginning in the 1920s.

While the quantity and quality of natural areas that provide the deer with shelter and food has diminished in North America since European settlement, biologists believe that farming, conversely, has helped deer proliferate in some settings. Crops such as soybeans, alfalfa and corn in the fields surrounding Allerton provide the deer with an abundant, preternatural food supply that they use to supplement their diet of natural vegetation. Even in the winter months, the deer are able to sustain themselves by browsing on waste grain left behind in the fields during the harvest.

Multiple births – sets of twins and even triplets – are not uncommon, as does in the Allerton area tend to be in prime physical condition and reproduce at steady rates until they die. Mild winters and low natural mortality from predators and disease are helping the deer herds flourish at Allerton and elsewhere in the region.

According to some estimates, a deer herd can double in size every six to nine years if it has sufficient food, low natural mortality and is not susceptible to hunters.

“In part, what’s driving the herd’s growth is how well the fawns survive,” Warner said. “There’s not much mortality pressure on them. We’re finding out that ‘let nature take its course’ is impractical now because we have so many things out of whack.”

Deer also are highly adaptable, Warner said, “and able to learn and adjust their habits more than biologists ever anticipated,” changing their behavioral patterns to find shelter and food and raise their young despite changes in their habitats.

At Allerton, the burgeoning herd is a growing concern because of the extensive damage the deer do to the gardens and the forest.

Staff members report that every year deer consume nearly all of the annual and perennial plants around the conference center and nearby buildings. Last year, the deer consumed a substantial amount of ornamental vegetation around the conference center alone, and overnight ate all the flowers that student interns had laboriously planted one day – leaving behind only empty flowerpots and hoof prints.

Deer also find the trees and shrubs rather tasty and have grazed on yews up to 6 feet from the ground. Hardwood seedlings, it seems, are highly appetizing to the hooved diners, and during the past 30 years, only one oak seedling in the forest’s study plots has managed to elude the deers’ voracious browsing. In addition, memorial redbuds, oaks and other trees near the conference center had to be replaced because the deer destroyed them by rubbing on them.

In 1987 an electrified fence was constructed around the park’s core – the meadow, the conference center and the formal gardens – in an attempt to exclude the deer from the cultivated areas. However, the deer quickly learned how to circumvent the fence, which today serves as little more than a reminder that the deer are not easily deterred.

The herd’s travels throughout the park and the adjacent 4-H camp also are damaging the turf and hiking trails, creating “game trails” that dissolve into mud wallows when it rains, said Jim Gortner, interim director of operations and conference center manager.

Aside from the costs associated with replacing plants, trees and soil damaged by the deer, there also are growing concerns that the burgeoning herd may pose a threat to the park’s ecosystem. The herd’s feeding habits are diminishing the diversity of plant species throughout the forest – which ultimately may eradicate food sources and habitats for other fauna. Deer consume native wildflowers and saplings, which enables invasive, often non-native species of plants such as garlic mustard, bush honeysuckle and multiflora rose, which deer find unpalatable, to thrive. The non-native plant species propagate rapidly and are dramatically changing the composition of the forest’s understory vegetation, although staff routinely remove invasive plants by hand and with controlled burns. The intrusive plant species also are proliferating because limited resources hamper staff’s containment efforts.

The teeming deer population in and around the park also is a concern because diseases are prone to spread rapidly among high-density deer herds. Deer can foster Lyme Disease, a tick-borne disease that can be transmitted to humans. Based upon inspections of deer taken by hunters in the Piatt County area in recent years, there is evidence that deer ticks (Ixodes scapularis), the primary vector for Lyme Disease, are on the increase in the area.

David Schejbal, associate vice chancellor and director of continuing education, said that UI officials are exploring various options for managing the deer herd at Allerton and will be developing a plan in the near future.

However, even when deer populations are brought under control in a region, it can take a decade or longer before the vegetation begins to show recovery from the damage the herds have wrought, Warner said.

“We’re at a point now that if we want to protect Allerton Park’s natural vegetation, we have to do something about the deer. While deer are a valued and important part of the ecosystem, a hands off approach at this point is unacceptable,” Warner said.

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