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The white-tailed deer is the only large native mammal still living in the wild in northern Illinois. The big predators–black bear, timber wolf, and puma–were wiped out more than a century ago. The other hoofed animals–elk and bison–survive only in captivity.
For the millions of us who live our lives entirely within the boundaries of a world created by humanity, the sight of a deer bounding through the woods is the most thrilling experience of nature we can expect to have. Lately, in the Chicago area, that experience is becoming a bit too common. Many of our forest preserves are under assault by deer herds grown so large that the preserves can no longer support them.
In my last column I described the damage that large numbers of deer can do to a natural area. With no effective checks on their numbers, deer can eat their favored food plants to extinction and almost eliminate the forest understory and the animals that depend on it for food and shelter.
In Cook County, the Ned Brown Preserve has suffered damage so heavy that it may take decades to recover–if indeed it ever does. In Lake County, the Ryerson Conservation Area, an old-growth sugar-maple forest along the Des Plaines River, is just beginning to show signs of damage from a deer herd that’s about five times the carrying capacity of the preserve. In hopes of halting the damage before it becomes too severe, the Lake County Forest Preserve District is seeking permission from the county board to shoot about 40 of the 50 deer now living at Ryerson.
As expected, this proposal has elicited public outcry. Killing deer is not popular. Various alternatives have been suggested. In this column, I’m going to look at the possible courses of action, the lethal and nonlethal methods available for dealing with too many deer.
Feeding the deer is one suggestion that invariably pops up. It is based on the assumption that the deer will visit the feeders instead of eating the plants of the preserve. It does not work; it backfires. With a reliable food source to help them, more deer survive the normally hard winters and they reproduce bountifully. Feeding causes more deer. James Witham, who has been studying our deer herds for the Illinois Natural History Survey, thinks so little of feeding that he believes there should be county ordinances forbidding private citizens from putting out deer food in their backyards.
The two serious nonlethal methods are transportation and sterilization. Both have been tried at preserves around the country. The Schlitz Audubon Center in Milwaukee has been transporting deer for seven years, and they have been able to maintain populations at reasonable levels. Schlitz Center is quite small–only 185 acres–and it is surrounded on three sides by suburbs. The fourth side is Lake Michigan.
The site manager of the center decided against shooting the animals. It seemed impossible to do it safely in such a small preserve; he didn’t like it personally, and he was afraid that many of the donors who are the center’s support would be offended by it.
During the first five years of the program, deer were captured with hypodermic darts loaded with tranquilizers. The deer were attracted by corn and apples put out at a feeding station. The trappers shot from a building 20 meters away.
The difficulty in darting deer is that the charge behind each shot must be precisely matched to the distance. Shoot too hard and you injure the animal. Shoot too soft and the needle falls out. This limitation on the technology explains the need for a baited feeding station as the only certain way to get a deer to stand a known distance from you.
In 1986, the center switched to a trap of its own design. The animals enter in search of food and can’t get out. They walk directly into a transport box, which can be loaded on a truck; the whole operation requires only one human.
The deer are taken to areas outside Milwaukee County, areas where hunting is allowed. The trapping is all done in December and January. Food shortages are by then a spur to the deer. Hungry animals will come to bait. Well-fed animals often will not. Midwinter is also the time when the fawns born the previous spring grow old enough to go out on their own. The winter release also gives the animals 10 or 11 months to get acclimated before the next fall’s hunting season.
James Witham and Martin Jones, also from the Natural History Survey, also transported some deer they took from the Ned Brown Preserve. They moved 52 animals to U.S. Army land near Joliet. They only lost one deer to injury. Radio collars, which Jones monitored for several months, showed that many of the transported animals got along well in their new home.
The weaknesses of transportation start with the fact that the white-tailed deer are doing well throughout their range in the U.S. Nobody, certainly nobody in the eastern half of the country, needs more deer. All the available habitat seems well filled, and local herds do a fine job of maintaining their numbers. Transported animals often die, perhaps because they cannot find space for themselves. And where they do survive, they may be displacing native deer.
The more fundamental objection has been stated by Leon Nielsen, the executive director of the Wisconsin Humane Society, and one of the people who set up the Schlitz program. “As a rule,” he wrote, “translocation of deer from urbanized areas to rural or wild habitats has no beneficial ecological consequence.” In other words, it is an out-of-sight out-of-mind approach, rather like putting hazardous wastes in landfills. If we can’t see the problem, then there is no problem.
Harmful consequences mentioned by Nielsen include “transmission of diseases or parasites; competition for food and other resources with a resident deer population; loss of genetic integrity of subspecies through hybridization; and dominance by translocated species causing undesirable changes in plant and animal communities. Lacking familiarity with the release area and its resources, and usually being without the natural wariness of wild deer, urban deer may also fall victim to starvation, predators, poachers, and hunters.”
The disease question gains some urgency from the recent appearance of Lyme disease in the Chicago area. Lyme disease is a bacterial infection spread from deer to humans by the bite of a tick that feeds on both of us. Lyme disease is unlikely to kill you, but it can make you very sick for long periods if it is not promptly treated. Symptoms include nausea and, in most cases, inflamed joints. A few develop serious complications, including heart problems and symptoms that mimic those of encephalitis and meningitis. This is not something we want to transport to new lands.
Sterilization has been suggested as a way to handle overpopulation. A group called the Concerned Veterinarians and Citizens Committee to Save the Ryerson Deer has submitted a sterilization proposal to the Lake County Forest Preserve District. The proposal calls for darting the deer with Telazol, a “non-narcotic, nonbarbiturate injectable anesthetic characterized by rapid induction, profound analgesia, and a wide margin of safety.” Once captured, the bucks will be vasectomized. Implants of a mixture of estradiol and progesterone will be inserted in the cervical musculature of the does. These implants are supposed to suppress fertility for five years.
This approach was tried before, on Angel Island in San Francisco Bay, on the black-tailed deer, a close west-coast cousin of our whitetails. The deer herd on the 600-acre island numbered 300 animals in 1980. A major relocation operation in 1981 reduced it to 50 animals, but by 1984, the herd was back up to 250 and obviously climbing rapidly. In that year, the San Francisco Society for the Prevention of Cruelty to Animals began a major effort to trap does and implant a chemosterilant in the muscles of their right shoulders.
Every evening for 91 days, volunteers set out 16 traps on the island. They checked the traps before dark and again early each morning before taking them down for the day. The volunteers also moved the traps periodically.
After a total of 1,456 trap nights, the volunteers had made 205 captures, an impressive total. However, those 205 captures represent only 70 animals: 37 bucks that were tagged and released, 30 does that were fitted with implants, and 3 animals that died from the shock of capture. “Recaptures were common,” the report dryly notes. In every wild population, there are likely to be a few trap-happy animals that get captured over and over again.
Of the 30 does sterilized, only 15 were adults likely to breed that year. Cutting the population of breeding does by 15 animals would reduce the fawn crop by 20 to 25 deer, but the rest of the herd could make up much of the deficit. Volunteers did most of the work on this job, and housing and food were donated, but the SPCA still spent $30,000 on a project that did nothing more than slow down the natural growth rate in the herd.
The Concerned Veterinarians want to start work in mid-November. Between then and mid-March, they are going to try to capture every deer in Ryerson with the goal of reducing the 1989 fawn crop to zero. Their own calculations suggest that they will need to sterilize at least 80 percent of the population to make a significant dent in reproduction. If they achieve that they expect to pick up the missing 20 percent a year from now during phase two, leading to a 1990 fawn crop of zero.
Experienced deer catchers are doubtful about these capture predictions. Certainly the Angel Island numbers make an 80 percent capture rate seem impossible. Deer are easier to catch in this part of the country because food shortages are common in winter and deer are more likely to come to bait when they are hungry, but 80 percent in one season “may not be possible,” according to Leon Nielsen. An effort commensurate with the level of difficulty would take “many, many, very many man-hours.
According to Nielsen and to Martin Jones of the Natural History Survey, stalking deer through the woods is a very demanding, time-consuming process requiring great skill. You couldn’t hope to get 80 percent that way, especially when you are operating with a dart gun that must be fired from a preset distance and whose maximum effective range is about 50 yards.
So you need to set up feeding stations and place marksmen and veterinarians in blinds near them and have everybody wait for many, many, very many hours.
At Schlitz Audubon Center, the darts had radios in them. Telazol, the anesthetic the veterinarians want to inject at Ryerson, takes four to five minutes to take effect. Dr. Steven Nusbaum, a veterinarian who helped write the Ryerson proposal, believes that the deer will not go far and that they can be tracked. Leon Nielsen disagrees. He says that a panicked deer can go a long way in four to five minutes, so the radio, even though it adds to the expense, is necessary for tracking. Once captured and sterilized, the deer would be injected with three million units of penicillin “for prophylactic purposes,” and then released.
Leon Nielsen suggests that to have any hope of getting close to the 80 percent goal the veterinarians would need to scatter at least ten traps around the 550-acre preserve. The traps would be equipped with radio alarms that would notify headquarters whenever an animal blundered in. With traps and dart guns and many man-hours, you might have a chance to capture enough deer to make a difference, but it would be a slim chance. Nielsen again: “It is very difficult to trap 80 percent of any wild population in a single season.”
The sterilization option is long-term thinking, which we ought to be doing. However, we also have a short-term problem at Ryerson. Sterilized deer still eat and they may continue to do so for many years. The Illinois Natural History Survey study found that herds in the metropolitan area average much older than herds in counties where hunting is permitted. The life span here is 10 to 14 years. It is 7 to 8 years in hunted populations.
Sterilization is difficult–perhaps impossible–very expensive, and it does not address the current problem; it does not immediately reduce the deer herd at Ryerson.
The introduction of a suitable predator has been suggested as a way to let nature deal with the deer. Wolves and pumas are not likely to find Lake County congenial. Coyotes live around here. They may someday invade Ryerson on their own. Coyotes are effective predators on fawns, but they rarely take adult deer. It might take years for them to make a difference, and they will bring problems of their own. The first time somebody’s Yorkie gets killed and eaten in the backyard, the outcry will be very loud.
My own opinion is that we have to shoot some deer at Ryerson. Transportation is pointless, an expensive game that just moves the problem. Sterilization is very uncertain. At best, it will not significantly affect the deer population for a year or two. Shooting is the only way to make a significant dent in the breeding population right away.
However, I also think that we should be looking at sterilization as a more long-term alternative. Sterilization at this point is an experimental procedure, but somebody should be making the experiments. Problems with excess deer are going to be even more common in the future and we need to develop a variety of strategies for dealing with them.
There are other questions about this sort of intervention. Both shooting and sterilization remove genes from the pool, for example, with effects that we really cannot predict. We need to be aware of this and to monitor as closely as possible the effects of our actions.
Excess deer are just one aspect of a more general problem. How do we sustain natural systems and therefore the individual species they support in a world where nature has been isolated into tiny islands? Our experience so far suggests that increasing intervention may be necessary to prevent our natural areas from degenerating into weed yards supporting depauperate animal populations.
Most of our intervention seems entirely benign. We cut down invading buckthorn shrubs or poison purple-loosestrife plants; plant native prairie species or put out nest boxes to attract bluebirds. The Lake County Forest Preserve District has been a leader in developing and applying methods for carrying out this kind of intervention. As a result, they have many quality preserves where healthy populations of large numbers of native plants and animals still exist. Their proposal to shoot deer at Ryerson continues this leadership. They have identified a serious problem and they are making a serious attempt to deal with it. Superintendent of conservation Dan Brouillard and general superintendent Jerrold Soesbe deserve credit for their willingness to take political heat in support of a necessary action.