Experts Asked: Does Deer Culling Reduce Tick-Borne Disease?

By Kendra Bobowick

As Newtown grapples with managing tick-borne diseases, surrounding towns’ officials recount similar concerns and results of deer culls.

Automobile accidents. Lyme disease. Ecological destruction.

“Only one culprit translates to all problems,” said Wilton’s Director of Environmental Affairs Patricia Sesto. The culprit is deer. Public safety issues including illness were among the reasons that deer management “was warranted” in Wilton, she said. In 2002-03, the town’s Deer Committee recommended herd reductions.

Controlled hunts have since taken place on as much as 1,200 acres of land, a size that had increased from 700 acres.

The one driving question that has preoccupied Newtown’s Tick-Borne Disease Action Committee asks: Do efforts to reduce deer and therefore tick counts also reduces Lyme?

Ms Sesto replied, “I don’t have a good way to measure” the results of deer reductions and Lyme incidents. “We don’t have a good way to track that.”

While the health benefits of deer herd reduction are unclear, the environmental benefits are becoming clear.

Ms Sesto is unsure of the current deer density, but by the fifth year of deer management in Wilton, she saw results on the hunted acres that indicated a positive change in the environment. “We’re looking at property to see if it’s recovering and you can definitely see a difference in the forest.” Along with understory regeneration, she also noted saplings and wildflowers that had not been occurring in recent years.

She considers how much the controlled hunt has bumped up overall hunting in Wilton. The controlled hunt participants “were also the hunters that were responsible for much of the hunting on private land. Effectively, we just moved their hunting locations, although the controlled hunting properties were more fruitful, so Wilton’s numbers increased, but not as much as we would have liked.”

A Ridgefield resident, Ms Sesto also co-chaired her hometown’s Deer Committee that included a 19-member study group. Eighteen members agreed that the deer problem warranted action. The group’s charge had been to understand problems of deer in relation to Lyme, car accidents, and overbrowsing, and targeted the count to 20 deer per square mile or less for ecological reasons. After five years, she has no conclusions yet regarding effects of the cull. “It took us a while to get here, especially given the limitations to access to property.”

Who is hunting that land? Ms Sesto said, “I believe the composition of Ridgefield’s hunters is less dependent on local hunters. They are bringing new hunters into town to add to those that already had hunting spots on private properties.”

Darien’s Deer Management Committee Chairman since 1997, Kent Haydock, also a member of Fairfield County’s Municipal Deer Management Alliance, said results in his town’s controlled hunts begun in 2005 “took a long time” finding acceptance. “We didn’t at first think the town was ready for it and by 2005 we felt it was viable.”

Reducing Accidents

The results? “It’s hard to count deer, but the number of accidents has been reduced.” Regarding tick-borne disease he said, “We don’t have a fix on the disease cases.” Like other towns, landscape destruction was also a factor. “They are decimating our woods.”

Initially Darien’s deer management panel coordinated hunting between the landowners and hunters. The town’s land trust soon participated. Surveys of residents followed. “There have been no real negative feelings about having a hunt,” he said, then laughed, “If you ask if they want it in their yard, well, the number goes down.”

Ornithologist Stephen Patton at Devil’s Den preserve in Weston said a deer management program has been ongoing for roughly ten years. Based on aerial surveys, the count is down to roughly 25–30 deer per square mile, which is “substantially less than we understood it to be” previously. “Actually people see fewer deer and there are fewer accidents on the roads.” Like Ms Sesto, he also has seen the return of flora begin to grow where it had not been in recent years. Trillium and bloodroot have returned to places other than hard-to-reach areas where deer could not get to them.

With about 20 hunters on 1,700 acres, Mr Patton said the controlled hunts are done carefully. The den is closed when hunts are conducted and neighbors are notified. The method is “rifles over bait,” he explained.

Will the recreational hunting get the job done, or will more effort be needed? “He said, “We’re seeing more effort to bring down the population to what’s healthy for the forest,” he said. What about disease? “And it would presumably help Lyme,” he said.

The Elusive Deer/Disease Correlation

Entomologist Kirby Stafford with the state’s Agricultural Extension Station would be the best person to speculate about the relationship between a drop in deer count and a reduction in tick-borne disease, Mr Patton said.

Mr Stafford pondered the question. The relationship between a deer cull and Lyme disease is “not a direct equation,” he said. The question is difficult to answer.

Studies he has published do not measure Lyme incidents, but number of ticks in an area. He also said: “The number of ticks is down so you assume the risks for Lyme go down. The devil is in the details. Assume if the number of deer is down, the tick number is down and Lyme is down.”

The only study of which he is aware that looks at Lyme in relation to a deer cull is by Howard Kilpatrick with the state Wildlife Division, who studied Groton’s Mumford Cove. The state’s Managing Urban Deer In Connecticut, which Mr Kilpatrick prepared, specifically talks about the possible correlation between deer numbers and disease based on the Mumford Cove study.

The booklet states: “Although the threshold at which deer densities need to be reduced to document significant reduction in transmission rates of Lyme to humans is unknown, the relationship between deer abundance and human cases of Lyme was well documented in … Groton from 1996–2004. The deer population in Mumford Cove was reduced from about 77 deer per square mile to about 10 after two years of controlled hunting … Reducing deer densities was adequate to significantly reduce the risk of humans contracting Lyme disease in Mumford Cove.” (See ct.gov/dep and search for the publication for more information.)

Wednesday evening guest Anthony DeNicola, PhD, is with the White Buffalo, a 501(c)(3) nonprofit wildlife management and research organization dedicated to conserving native species and ecosystems through damage and population control, as stated on WhiteBuffaloInc.org. He also addressed the committee’s questions about deer population as it may relate to Lyme.

Did Dr DeNicola agree that the thought that ten deer per square mile would reduce Lyme, and did he think it was possible to get the numbers in Newtown down to ten? First, he did not think ten per square mile was going to happen in Newtown, primarily because Newtown officials may not be ready to spend the necessary money. He also referred to Mr Kilpatrick’s Mumford Cove study. Like Mr Stafford, Dr DeNicola said, “You can reduce the volume of ticks by reducing deer, but I don’t know about the decreases in Lyme.” He has never contracted Lyme disease, which he attributes to thoroughly checking himself and his clothing daily.

About checking for ticks, he said, “Obviously the public doesn’t do it or we wouldn’t be sitting here in this room.”

Members noted that no comprehensive study exists for how deer counts affect Lyme disease.