Planet Earth

One Marsupial Too Many

Australians face the same problem with koalas as Americans do with deer. The pesky critters seem too cute to kill but are destroying a lot of precious habitat

By Mary RoachDec 1, 2000 12:00 AM


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A koala does not expect to have a bad day. thirty feet up a gum tree, it lives beyond the reach of predators, surrounded by eucalyptus leaves, its one-stop source of food and water. Koalas spend four hours a day eating and the remainder of the day sitting looking cute in the fork of a tree. Digesting eucalyptus fiber is the toughest thing life demands of them. Perhaps this explains the lack of concern on the face of a koala soon to be known as Z-018, whose postprandial nap has been spoiled by a group of noisy bipeds carrying gunnysacks and long plastic poles on the ground below. The koala watches the activity below the way a dog will watch TV. She has no idea she is about to have a very bad day. The men with sticks work for Ecoplan Australia, a private consulting firm experienced in controlling wildlife populations. Ecoplan, together with the national Cooperative Research Centre for Conservation and Management of Marsupials, has been contracted by the Victorian state government to help solve the Snake Island koala problem.

Snake Island, an uninhabited 10-by-5-mile manna gum and banksia woodland off the coast near Melbourne, is lousy with koalas. With no predators and little disease, island koalas are increasing far faster than the eucalyptus trees they browse. The last census, in September 1999, put the koala population here at 2,400, or almost an animal per acre of habitat— double what the island can sustain. Walk the island's tracks with your eyes trained on the treetops, and you cannot fail to spot koalas: fur balls attached like pussy-willow fluff to the tree limbs. If Snake Island's koalas continue to multiply at their current heady rate, the eucalyptus will soon be gone, and the koalas will start to starve. They are their own pests.

The simplest and cheapest solution would be to hire sharpshooters and cull the animals, as is frequently done with overabundant, sapling-devouring white-tailed deer in the United States. But this is impossible, for much the same reason it is becoming less possible with deer. Wildlife management types call it the Bambi effect: Citizens do not easily tolerate the killing of cute animals. In fact, urban Americans rate deer higher than any other wildlife species, even as those same deer defoliate their parks and gardens. In a 1999 survey undertaken in deer-plagued Cayuga Heights, New York, 80 percent of the residents felt the deer problem was intolerable, but less than one third supported killing them.

Few "charismatic megafauna," to use the wildlife management catchphrase, evoke the Bambi effect as dramatically as koalas. Koalas are the standard-bearers for mammalian cuteness. With eyes set side by side in a snoutless face, their looks are appealingly humanoid. Hold them aloft, and their legs hang bowed like a toddler's. No wonder we can't bear to see them killed. They remind us of us.

"When someone suggests culling koalas, all hell breaks loose," says Peter Menkhorst, a wildlife policy officer who oversees the state of Victoria's management plan for koalas. A 1996 proposal to cull koalas on nearby Kangaroo Island sparked a public outcry and a heated media debate. For a while, koalas were simply relocated from Snake Island to patches of eucalyptus forest on the Australian mainland. Hundreds of koalas later, there's no place to put them. Birth control, in the form of slow-leaching hormone implants, has also been tried— both on koalas and on deer. Although the implants are effective, the labor necessary to capture the animals, insert the implants, and regularly replace them makes the undertaking prohibitively expensive. The same holds for vasectomies and tubal ligations.

Here comes immunology to the rescue. Koala Z-018 is about to become a test subject of a new approach to wildlife population control, called immunocontraception. The idea is to trick the immune system into treating an animal's own eggs as though they were invaders— something to develop antibodies against. It's essentially a vaccine that primes the immune system with a close stand-in for the real thing. In this case, the vaccine is made from a protein found on the coating of a pig's ovum, called porcine zona pellucida. To date, results have been promising. Among brushtail possums, considered New Zealand's most damaging wildlife pest, immunocontraception blocked fertility in about 80 percent of treated animals. Among Australian tammar wallabies, the vaccine proved to be 100 percent effective. In the United States, a trial of immunocontraception on white-tailed deer resulted in an 87 percent reduction in fertility.

Immunocontraception has probably received more attention and research dollars in Australia than in the United States, but the technique was first used on wild animals by an American, biologist Jay Kirkpatrick, who treated feral horses in the mid-1980s. Kirkpatrick was building on the work of researchers who were developing immunocontraceptives for people. It's possible; and not all that uncommon; for a woman's infertility to be caused by an immune reaction to her husband's sperm.

Wildlife immunocontraception works via injection of an ova protein into the female's muscle or under her skin. Because the bloodstream is the immune system's central weapons depot, and because ova aren't normally found there, the koala develops ova antibodies, protein molecules poised to attack the next egg they encounter. If all goes as planned, koala Z-018's immune system will henceforth disable her own eggs. But first they have to catch her.

Coaxing a koala out of a tree is harder than one would think, for koalas are surprisingly quick and stubborn. The koala catchers; Ecoplan biologists Matt West and Keith Cherry, with the visiting Menkhorst lending a hand; are using telescoping fiberglass poles crowned with flapping pieces of plastic garbage bags to spook the koala. One need only shake them in the animal's face and it will back down the tree and into a waiting gunnysack. Or so the theory goes. The men extend their poles. The garbage-bag phantoms weave and bob as they rise through the foliage. The scene has the look of an avant-garde puppet show. West swings his pole in close and shakes it. Koala Z-018 shrinks back, mouth open and paws flung out in front of her chest in a comic-book gesture of surprise. Meanwhile, her distress calls rake the afternoon calm, at once squeaky and hoarse, as though she were coughing up a small squeeze toy.

Koala Z-018 summons all the energy her gut-slowed metabolism can provide. She starts to back down, as West had hoped, but then turns and leaps, monkey-fast, across two feet of air to the other prong of the tree's forked trunk. Before the men have time to reposition their poles, she has scrambled back up, higher than before. Then West puts on a nylon climbing harness and goes up after her. The distress calls of koala Z-018 are more urgent now, a string of truncated squeals like sneakers on a basketball court. As West hustles her down the tree, she suddenly panics and hurls herself into the air, dropping the remaining 25 feet to the ground as onlookers clap their hands to their faces.

No worries, as Australians like to say: Koalas are apparently as unbreakable as the teddy bears they resemble. She hits with a quiet thud, bounces slightly, and is on her feet, scrambling. Cherry lunges for her. He grabs the scruff of her neck and lifts her up, his other hand supporting her from below. He holds her at arm's length, for she is wet with urine and ambitiously hostile, growling and hissing like a whip-peeved circus tiger. Cherry's caution is well warranted: A few months back, when park workers were giving vasectomies to some of the island's males, a koala bit clear through a volunteer's palm. Menkhorst picks up a burlap sack and holds it open. Cherry tries to drop the koala inside, but she has her limbs spread wide like a lobster approaching the pot. The men wrestle her in and tie off the sack.

It has been 25 minutes since koala Z-018 was spotted, and her ordeal is only halfway over. Before giving her a shot of tranquilizer and a dose of the immunocontraception vaccine, the biologists will draw the koala's blood to establish a baseline of her immune system activity. Then they will outfit her with ear tags and a radio collar so the crew can track her down in a month's time to recheck immune levels and give her a booster shot if her antibody levels aren't high. The whole process will take upward of an hour.

For immunocontraception to be accepted by wildlife management professionals in Australia and in the United States, the process will need to be streamlined and the costs brought down. In the United States, administering multiple-shot vaccines costs between $300 and $400 per deer. Since July, a series of single-shot (no booster) vaccine formulations have been tested on white-tailed deer at Pennsylvania State University. And both Australian and U.S. groups are working on vaccines that can be administered with a dart gun, which would eliminate the need for catching and tranquilizing the animals. (In South Africa, researchers recently used helicopters to shoot female elephants with immunocontraceptive darts. After 10 months, only 20 percent of the elephants were pregnant, compared with 80 percent of untreated females.) Once there's a vaccine that can be administered in a single shot with a dart gun, the cost should be on a par with that of sharpshooting.

An injection isn't the only way to introduce an ova vaccine. Oral vaccines also work, provided some measures are taken to protect the vaccine from stomach acid. Seals have been successfully treated with a lipid-coated ova protein that passes through stomach acid intact. The National Wildlife Research Center, in Fort Collins, Colorado, has just begun an ambitious bioengineering project that would embed the ova protein in a yeast, which also survives stomach acid. Still, treating deer will be a challenge. As ruminants, they have particularly thorough digestive tracts. And giving koalas oral vaccines will be nearly impossible unless biologists spray entire eucalyptus trees with lipid-coated vaccines. Oral vaccines are also a bit too broadly effective: Animals other than the target species may wind up eating the bait and becoming sterilized.

In New Zealand, researchers are testing a bioengineered virus that could deliver a vaccine to brushtail possums. To prevent the virus from spreading, they're using a "crippled" form of it that has been engineered not to replicate. The virus would be sprayed in a possum's face when the animal puts its head inside a feed box. Lowell Miller of the National Wildlife Research Center says this particular procedure will not be coming soon to America: "We'd be run out of the country if we tried to use a virus. We'd never get it registered with the Food and Drug Administration."

Even immunocontraceptive shots may have a hard time earning government approval, Miller believes.. "Although scientists are certain that the deer meat wouldn't sterilize humans, they still have to prove it," he says. For animals that (most) people don't eat— coyotes, ground squirrels, bears, raccoons— getting FDA approval is somewhat easier. But whoever markets a vaccine will have to demonstrate the safety of every possible application. "Each species has its predators that the FDA might be concerned about," Miller says. "A bald eagle might take a coyote pup that had been contracepted. You'd be in trouble if you didn't test for that." The research could cost up to $20 million, and a pharmaceutical company would pay for it only if it could make the money back on the vaccine. So far, no one has stepped up to the plate.

Miller believes the domestic livestock industry is immunocontraception's brightest hope. "There's enough money in the pig industry to develop a product. And there may be enough money in the product that they'd be willing to ante up the money to test some of the wildlife applications." Barring that, if the deer problem continues to grow, Miller says, it's possible that the government will subsidize the vaccine. Compared with the cost of killing deer and koalas outright; and contending with outraged animal-rights groups; it may even turn out to be something of a bargain.

From the perspective of a visitor slogging through it, the plant life on Snake Island seems in pretty good shape. Unlike deer-plagued forests in the States where saplings are bare from the browse line down, the bush here is dense with thickly leaved trees: melaleuca and spindly acacia, all of them five or six feet tall, a crowded cocktail party of plants. But then a koala-ravaged gum tree that looks like a fish spine left behind on a dinner plate pops into view. And the number of denuded manna gum trees is steadily increasing. If the koala population were left unchecked, Menkhorst says, it would double in about eight years, and the island ecosystem would be seriously damaged within two.

With koala Z-018 in tow, West bushwhacks his way back to the road to join immunologist Anne Kitchener, who hails from the University of Newcastle in New South Wales, and Ecoplan director Bryan Walters, both of whom wait by the group's all-terrain vehicle. The animal is slung over West's shoulder, quiet now in the dark of the sack. Kitchener knows better than to open the sack. She readies a shot of tranquilizer and sticks it through the fabric. A minute later, Walters peels the burlap down to the koala's midsection, making her look like a competitor in a children's sack race.

For the duration of the proceedings, koala Z-018 will remain about 80 percent unconscious, more plush toy than wild animal. Kitchener shaves a patch of the koala's forearm and searches for a vein to draw blood. That done, Walters clips a pair of colored plastic ID discs onto Z-018's ears. Walters is a soft-spoken Gepetto of a man, who calls his subjects "girl" and "darlin'. " He clearly doesn't relish the task at hand. Although this is being done for the koalas' benefit; better a few bad days than starvation; it's hard not to feel for the little guys. "It's a big step to start playing God and meddling with fertility," Walters says, idly rubbing Z-018's belly. "Whatever we do, we must do in the most benign method possible."

How benign, then, is immunocontraception? Does infertility affect an animal's well-being? Does it change a group's behavioral dynamics? Walters says that infertile females are usually healthier and longer-lived than females with offspring, because they can expend more energy on themselves. In fact, some biologists worry that immunocontraception will partially backfire for that very reason: "If you sterilize part of the population, the rest could respond with increased fecundity because there's more food available," says Roger Pech, of the Wildlife and Ecology division of the Australian Commonwealth Scientific and Industrial Research Organisation in Canberra. One study of rabbit populations in Australia showed no increase in fecundity after immunocontraception. But the young rabbits lived longer, which increased their numbers.

As for infertility's social effects among koalas, little is known. Among U.S. deer, immunocontraception does interfere with the dynamics of a herd, mainly by prolonging the rut season. The white-tailed deer rut season is normally two to three weeks in November. But if the doe doesn't get pregnant, she goes into estrus again, and again, for up to four months. "We've seen deer cycle clear up to March," says Miller. "Turns out it's such a long breeding season that the alpha bucks actually give up and the young bucks take over." The prolonged rut season doesn't just disrupt a herd's social fabric, it makes deer more of a hazard to motorists. "Rut season is when deer are moving back and forth a lot and crossing roads," Miller says. The longer the season, the more accidents deer are likely to cause. Every year, about 200 Americans are killed and 29,000 injured when cars hit deer. The total cost is thought to exceed $1 billion.

The ova vaccine, Miller says, is a better choice for monestrous species, like coyotes, that come into heat only once a year, regardless of whether the female conceives. For polyestrous species like deer, the NWRC is working on another option. Rather than disabling the female's egg, this vaccine would prompt a doe's immune system to disable a gonadotropin-releasing hormone, which initiates a hormonal cascade every fall that ultimately switches on the ovaries. Without the hormone, the doe's ovaries remain dormant year-round. Some would say this is cruel, that it robs an animal of its chance to have young; of its happiness, if you will. "I had a student who was really upset," says Miller. "I asked her, 'When you were a kid, were you happy?

You played with the boys and had a good time. And now you're a teenager. Are you as happy?' " Koala Z-018, at least, has already had a baby. Two of Walters's fingers are inside the koala's pouch. To someone who has never seen a marsupial pouch and was expecting something along the lines of a sweatshirt pocket, it's an unsettling sight. The opening is small and the pouch cleaves tight to the animal's body, so that Walters's fingers appear to actually enter the koala. Gently he pulls the baby partway out. It is pink and moist. You don't think "aw-w-w." You think "chicken parts." The koala is one of the rare species in which the adults are cuter than the newborns. Walters tucks the baby back in. Soon koala Z-018 will begin waking up, and West will take her back to her tree, then sit and wait until she emerges from the burlap. If she's still woozy and needs help climbing the trunk, he will give her a boost. Tomorrow will be a better day for her.

See for Peter Menkhorst's and Bryan Walters's paper outlining the history of, and potential solutions to, Victoria's koala problem. The Koala Rescue Foundation's Web site is: koalarescuefoundation/index.html.

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