Hunting boosts lizard numbers in Australian desert

The presence of humans rarely improves the lives of neighboring species. Yet a study shows that indigenous Australian hunters create prime habitat for a desert-dwelling lizard.

“It’s simply not the case that human activity always has a negative impact on ecological circumstances,” says ecological anthropologist Doug Bird of Stanford University.

The Martu, an aboriginal people in Western Australia, wield fire to hunt the lizard Varanus gouldii, known as sand goannas. In winter and spring, the Martu burn patches of brush to expose the lizards’ dens. Then people dig out the prey and roast the half-kilogram morsels over a coal fire.

The frequent burning creates a patchy mosaic of charred lands and vegetation springing up in various stages of regrowth. Unlike lightning-triggered fires that can wipe out large swaths of vegetation, the small human-lit fires promote a diverse collection of habitats. For example, fruit-bearing plants that feed humans and animals pop up during fire recovery.

Aboriginal peoples have lived in Western Australia for at least 35,000 years, and ancient lizard remains found at archeological sites show that people have hunted goannas for much of that time. To understand how the Martu have maintained their food supply for so long, Bird, Stanford collaborator Rebecca Bliege Bird and colleagues spent a decade monitoring changes in lizard group sizes, hunting success and habitat throughout a more than 46,000-square-kilometer section of Martu land.

Goanna populations were densest where the Martu hunted most. The paradoxical findings, reported October 22 in the Proceedings of the Royal Society B, reveal that the lizards prefer to dig their burrows in patches of mature vegetation within frequently burned regions. The lizards may prefer these edges because emerging vegetation from recently burned patches bears more food that attracts goannas’ prey, the researchers speculate.

The Martu understand their place in the desert as a key part of the relationships among plants and animals, rather than as landscape managers, says Doug Bird. So they believe that the ecosystem will collapse if they stop foraging and burning as they have done for millennia, he says.

Indeed, when the Martu and other desert foragers were forced to leave their lands between the 1950s and 1970s, surveys showed that 10 to 20 native mammal species went extinct and the numbers of 43 others dropped sharply. When the Martu returned in the 1980s, they reignited the small fires and biodiversity gradually increased, according to surveys previously conducted by the Birds and other scientists.

The research compellingly argues that “small-scale human societies can actually exist in an ecosystem without damaging it over a very long period of time,” says archeologist Bruce Smith of the Smithsonian National Museum of Natural History. “It’s just wonderful science.”

Editor’s Note: This article was corrected on October 23, 2013, to note that the species that went extinct in the 1950s through 1970s were mammals. It was further corrected on November 6, 2013, to clarify where the lizards choose to dig burrows.