Detecting Deer: New Method For Counting Population In Urban Areas

July 02, 1998

A biologist at Washington University in St. Louis and Missouri state conservationists have devised a new method to census deer populations in wooded urban areas. The method could serve as a model for similar urban/suburban regions nationwide facing the increasing nuisance and ecological nightmare of civilization colliding with nature.

Owen J. Sexton, Ph.D., Washington University professor emeritus of biology in Arts and Sciences, and Missouri Department of Conservation biologists Jeff Beringer and Lonnie P. Hansen employed air power, high technology and Mother Nature to count the number of deer at Washington University's Tyson Research Center, a 2,000-acre oak- and hickory-dominated ecological site on the outskirts of metropolitan St. Louis. Sexton is the director of Tyson Research Center. Their method relies on helicopter sightings from trained observers over a topography covered by about six inches of snow. The snow is helpful as a visual aid to distinguish deer from forest undergrowth. While helicopters flying over snow-covered terrain have been combined in other studies, no other scientists have employed a Global Positioning System (GPS), a sophisticated, geographical tool linked to a satellite that gives accurate geographical coordinates, minimizing the chance of the helicopter and observers straying off their designated flight paths. Departure from a flight path increases the chance of counting the same deer more than once.

The study also is the first over a wooded, urban terrain to report such a high detection rate of deer -- 79 percent. The detection rate is a numerical indication of the likelihood that all deer in the area were counted. Sexton, Beringer and Hansen published their study in the spring issue of Wildlife Society Bulletin, Volume 26, 1998.

Ecological Harmony

The census results were a surprise and will help Sexton and others develop a rational plan to keep the deer herd compatible with Tyson Research Center goals and size. The biologists counted a herd of approximately 125 deer at Tyson, well below an estimated 300 to 400 deer thought to inhabit Washington University's conservation research area in southwest St. Louis County. The deer population at Tyson has long thought to be excessive for its size. Non-scientific estimates before the survey ranged from 150 to as many as 400 deer at Tyson; wildlife biologists consider a herd of about 50 as ideal for ecological harmony in a 2,000-acre natural range.

"We are very happy with and encouraged by these results," says Sexton, who with Beringer and Hansen planned and conducted the study throughout 1996 and early 1997. "It appears that we will be able to keep deer numbers at Tyson controlled so that there are not too many deer for the ecosystem.

"Because Tyson Research Center is located at the edge of an expanding metro area, this study has many implications for other areas in the country," Sexton continued. "We think it is a major contribution to the solution of monitoring deer populations. One of the reasons people oppose a controlled hunt is that usually it's not clear how many deer there are in an area. This method gives you a very accurate baseline number to operate with and excellent parameters to monitor deer in a number of different habitats."

"Urban deer have become a major, growing problem," says Beringer. "We'll use this method throughout Missouri in conservation areas and elsewhere. If a community is going to have a controlled hunt, it's essential to have a sound, reliable method to count deer beforehand."

From Austin, Texas, to Chicago, Ill., to Gettysburg National Park in Pennsylvania, deer are becoming living lawn ornaments as development encroaches upon natural habitat. Deer populations have increased dramatically due to the lack of natural predators for many years and because deer cannot be hunted by humans in settled areas.

"It looks for all the world like the animals are encroaching upon humans, but it's the other way around," notes Sexton.

Counting The Herd

The biologists captured, marked and released 69 deer between Dec. 2, 1996, and Jan. 10, 1997. During a series of two-a-day flights the week of Jan. 11-17, 1997, biologists were able to count and compare the numbers of uncollared deer with the control count of collared deer to make a scientific estimate of the entire wild herd.

The census was performed with two experienced observers and a pilot in a Bell Jet Ranger helicopter traveling roughly 25 miles per hour some 200 feet above the ground, depending on conditions and terrain. The observers covered 65-yard transect plots indicated by bright-colored, numbered plywood squares fastened to the perimeter fence around Tyson. The flights were conducted one to two hours after sunrise and two to three hours before sundown. Flights were repeated 10 times over several days at the same time to lessen the possibility of a counting error.

"One of the key things is that we had a known population to start with," says Beringer. "That's a definite asset to any census. There have been many other attempts without a known population; then a pre-count assumption has to be made. But the GPS keeping us on our transect plots was the most important added feature to our study."

Excessive deer pose several problems for research at the Tyson Research Center, which is enclosed on all its borders by 8-foot fencing that is considered deer-proof. Deer face an inadequate food supply when they are overcrowded, which means that their health is affected and that fawns reach maturity at a much slower rate.

Too many deer accelerate the incidence of ticks, which coexist with deer. Some ticks carry Lyme Disease, which is a hazard to researchers, visitors and participants in field activities at Tyson and possibly to surrounding wildlife areas.

Too many deer also conflict with the goal of Tyson, which is to be a research center representative of pre-colonial times in eastern Missouri; excessive deer prohibits the flourishing of other fauna and flora species to achieve this goal. The surviving deer also tend to eat all available plants, including plants that botanists grow for research. Thus, researchers cannot conduct effective study and analysis of plants.

Sexton and his colleagues chose helicopters and snow cover as the best method for the deer census over a number of other tried, though not always proven, methods. Among them are: spotlight counts; deer drive counts; mark and recapture efforts; deer track counts; and counts with thermal infrared sensors attached to aircraft.

Sexton considers the survey to be the centerpiece of a national model for other urban and suburban areas to accurately determine deer numbers and monitor herd size.

"Of all the options, using helicopters over snow cover is the most efficient and cost-effective, especially for the terrain at Tyson, which is 90 percent oak-hickory forest," Sexton said. "This is a typical rural, and in some cases suburban, habitat found in the lower Midwest, much of the East and a portion of the South. We believe many areas in the United States will benefit from performing a census the way we have."

By Tony Fitzpatrick

Washington University in St. Louis

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