Once a year in the springtime, a lone plane takes off and flies a slow pattern over Carlton Hill station, a 3,600 square kilometre chunk of James Packer's Consolidated Pastoral Company, tucked into the extreme northeast of the Kimberley. As the plane circles, those aboard open up a special metal chute, and drop more that 1,000 little pieces of meat, one by one onto the open scrubland below. Each and every piece is laced with poison.

Besides 50,000 or so head of cattle, Carlton Hill and neighbouring Ivanhoe are home to dingoes, Australia's largest mammalian predator and the bane of graziers across the continent. "They take out cattle, and there goes our livelihood," says Stuart McKechnie, manager of Carlton Hill.

But one man wants the baiting to end, and for dingoes to once again roam Australia's wide-open spaces. According to Chris Johnson of James Cook University, and author of Australia's Mammal Extinctions: a 50,000 Year History, "Australia needs more dingoes to protect our biodiversity."

In the two centuries since Europeans landed, 18 species of native Australian mammals have become extinct - accounting for almost half the world total in that period. Desert rat-kangaroos, lesser bilbies, and pig-footed bandicoots have disappeared, and animals like the northern quoll are in serious decline. In his book, Johnson makes the case that these extinctions were caused by introduced predators - mostly cats and foxes - running rampant. Dingoes, he says, are the only way to control those predators and protect the native mammals that remain.

About 4,000 years ago, Asian seafarers introduced dingoes (Canis lupus dingo) to the shores of Australia. Over the ensuing millennia, these descendants of the wolf spread across the Australian continent and, as the Tasmanian tiger disappeared from the mainland, dingoes became Australia's top predators.

In 1788, Europeans began to colonise Australia. Agriculture spread across the continent, and graziers found that they could not safely keep their cattle and sheep where hungry dingoes lurked. So began one of the most intense, sustained efforts at pest control in Australia's history.

Over the last 150 years, dingoes have been shot, poisoned, and fenced in an attempt to keep them away from livestock. In the northeastern Australian state of Queensland alone, where the state government began rewarding kills as far back as 1877, hunters have collected about 1.8 million bounties for dingo scalps. But at the same time, as graziers tried to eliminate one native pest from Australia, Europeans settlers introduced some more of their own.

In 1860, the rabbit was unleashed on Australia by a wealthy landowner near Melbourne. They exploded across the continent. By 1980, rabbits had blanketed the mainland, save for the north of the Kimberley, the Top End of the Northern Territory around Darwin, and Cape York Peninsula. Rabbits provided a huge prey base for two other introduced species: the feral cat and the red fox.

The interaction between foxes, cats and rabbits is a huge problem for native mammals. In good years, rabbit numbers shoot up, and fox and cat populations grow quickly in response to the abundance of prey. When bad seasons follow, rabbit numbers crash – and the dwindling but still large fox and cat populations are left with little to eat besides native mammals.

Native Australian mammals generally reproduce much more slowly than rabbits, cats and foxes - an adaptation to prevent overpopulation in the arid Australian environment, where food can be scarce and unreliable - and populations decline because they can't grow fast enough to replace animals killed by the predators. Dingoes are the solution to this problem, says Johnson, because of how they interact with animals lower down on the food chain.

Dingoes are real bullies to cats and foxes, he says. Besides regularly eating the smaller predators, dingoes will slaughter them simply to lessen competition, steal their kills, and keep them from getting at food sources. Even the presence of dingo faeces can keep foxes away from potential prey.

As well as suppressing cat and fox populations, dingoes also regulate the numbers of kangaroos - animals too large to be affected by the small invasive predators. Dingoes keep them at moderate levels and prevent populations from going through 'boom and bust' cycles in response to changes in the environment. In areas where dingoes are baited, kangaroos can reach densities several times higher than in places where the dogs are free to hunt.

Dingoes put less pressure on smaller native mammals than do cats and foxes, according to Johnson, because dingo packs live in large, stable territories and generally have only one breeding female. This social structure limits their rate of increase, and thus their capacity for overpopulation. In the 4,000 years that dingoes have been in Australia, they have contributed to few, if any, mammal extinctions, he says.

Thousands of kilometres south and east of Carlton Hill lies Cameron Corner, a spot in the middle of the Strzelecki Desert marking the intersection of the states of South Australia, Queensland and New South Wales. Reaching out from this desolate spot for 2,500 km in either direction is the world's longest fence, standing two metres high and stretching from Jinbour in Queensland to the Eyre Peninsula on the Great Australian Bight in the south. Though its name changes twice as it meanders through the Australian outback, its purpose does not; the fence is there to keep dingoes out of southern Australia.

Though the barrier has been only partly successful in excluding dingoes from the south, it does split the two main types of livestock found on the continent: to the north of the fence, cattle predominate. To the south, sheep fill the landscape. In fact, Australia is a land dominated by the animals – 25 million cattle, 100 million sheep and only 20 million people.

Johnson can't see any way that dingoes could fit back into sheep country south of the fence. "Dingoes and sheep can't really co-exist because sheep are so easy for dingoes to kill that they'll hunt sheep in preference to anything else. If we've got sheep, we have to control dingoes."

In the vast cattle country to the north, it might be a different story because dingoes aren't as big a threat to cattle. Dingoes don't hunt cattle after the calves are much past two or three weeks old, according to McKechnie. And a 28-year study on three cattle stations in Queensland suggests that dingoes don't even prey heavily on the newborn calves unless their staple prey disappears due to deteriorating conditions like drought.

The same study, co-authored by Lee Allen of the Robert Wicks Research Centre in Queensland, suggests that the aggressive baiting programs used against dingoes may actually be counter-productive for graziers. Allen says that undisturbed dingo packs normally work together to take large prey like kangaroos. When dingoes are removed from an area by baiting, the area is recolonised by younger, solitary animals. These animals aren't capable of going after the large prey, so they turn to calves. In their study, some of the highest rates of calf predation occurred in areas that had been baited.

Not everyone is convinced that the science is valid, however. "Sounds like one of those things that the dingo crowd are likely to say because it fits their argument," says Mark Clifford, general manager of Heytesbury Beef, a firm that manages over 200,000 head of cattle on eight stations in the Northern Territory and Western Australia. "It's obvious if we drop or loosen control on dingoes, we are going to lose more calves."

Johnson argues that more dingoes could mean fewer kangaroos to compete with cattle for food, but Clifford doesn't buy the idea that dingoes will go after kangaroos when calves are around. "A few day-old calf doesn't take much doing to catch; I could run one down myself. I could never run a kangaroo down." Nor is he convinced of dingo's supposed ecological benefits, saying, "I'm not convinced that they manage to catch cats that often. I think they're more likely to catch little marsupials."

Back at Carlton Hill, McKechnie agrees that dingoes kill the wallabies that compete with his cattle for food, but he points out that in his neck of the northern parts of Western Australia, there are no foxes, and not very many cats. He doesn't see how relaxing controls on dingoes in his area will improve the ecological balance - but he knows firsthand the damage the predators will do to his livestock.

Johnson acknowledges the difficulties involved in balancing the stability of Australia's unique wildlife with the needs of one of the continent's largest and most important industries, but sees a need for a change in philosophy on the part of graziers.

"There might be a number of different ways of thinking through dingo management in cattle country," he says. "At the moment, though, that hasn't got through to managers. There's still just one prescription, and that is to bait as widely as possible."

For more information on Chris Johnson's book or to order a copy, visit Cambridge University Press.

---