Birth Control for Kangaroos: Scientists' Population Control Plan

Stephanie Peatling in Sydney, Australia
for National Geographic News
September 6, 2006
Australians often laugh at some people's notion that kangaroos hop down
the streets of the country's major cities. But in Canberra, the capital,
that's no joke.

Large numbers of the animals roam throughout the city, which was designed to be a series of satellite neighborhoods linked through pockets of bush by arterial roads.

Now the kangaroos—mainly the common eastern grey variety—have become a huge public safety issue, often getting hit by cars. (Related: "Kangaroo Attacks in Australia Spotlight Growing Turf War" [May 2005].)

Concern is so high that the government of the Australian Capital Territory (ACT), which includes Canberra, has called in marsupial reproductive experts to try and find a humane method of controlling the animals' numbers (map of Australia).

The researchers' proposal: kangaroo contraceptives.

The Animal Pill

John Rodger, a professor at the University of Newcastle's Tom Farrell Institute for the Environment in Callaghan, is heading the three-year program. He says the effort is inspired by humans' ability to control their own fertility.

"We have demonstrated that it's possible to have a fertility-control vaccine just as you or I have been vaccinated against polio or other diseases," Rodger says.

"So rather than poisoning or trapping or shooting [kangaroos], couldn't we do what we have done to ourselves? And can we apply the appropriate technology to achieve that?"

Scientists have already developed working contraceptives for kangaroos. Similar to some human treatments, these fertility-control methods include hormones that can be injected or placed under the skin.

"We have used molecular biology to make a protein coat around the shell of the egg," Rodger explained. "The protein is the layer the sperm must interact with, so if it is in an inappropriate state then the egg can't be fertilized."

Such injections can be given safely and efficiently to small numbers of animals in confined spaces, such as zoos.

But Rodger is dealing with numbers as high as 1,000 kangaroos per square mile (400 per square kilometer), according to one survey done by the Commonwealth Scientific and Industrial Research Organization based in Canberra.

At such densities, kangaroos are frequently sighted in the city's bush parks, along roadsides, and in people's backyards.

So Rodger faces a major obstacle: He needs to find the best way of distributing his product to a large number of animals.

Fed Up

Ideally, Rodger says, he would like to put pills or pellets containing these contraceptive proteins in a feeder and allow the animals to come and get them.

"[But] animals are generally frightened of new things, and we assume they like one thing rather than another," he said. "Would they like a pellet that's sweeter to make it more attractive? Then there are demography issues, like which kangaroos would be attracted to a feeder."

The pellets also need to contain a protective packaging to prevent stomach acids from destroying the active ingredients.

The next three years of research, Rodgers says, will determine whether what sounds like a good idea can actually be an effective control method.

In the meantime, animal welfare groups are watching the project closely—even though many are supportive of its aim.

"It is positive that the ACT government is investing effort in researching nonlethal kangaroo control methods," said Simone Gray, a spokesperson for ACT's Animal Liberation organization.

"Oral delivery seems to be a practical way to treat large numbers at once."

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