A sharp fall in native mammal numbers in the Northern Territory over the past 30 years is significantly due to feral cattle, horses, buffaloes and donkeys destroying their habitat, government-backed research has found.
Two studies published in peer-reviewed journals attempt to explain the severe decline in the populations of small and medium-sized mammal species such as bandicoots, possums and gliders since the 1990s.
While the NT’s vast landscape makes a true measure of animal numbers difficult to obtain, previous studies have estimated there was a 75% fall in mammal numbers in the Kakadu national park between 1996 and 2009 and a more than 70% reduction in the range of the brush-tailed possum across northern Australia since 1993.
The new four-year research project involved government and university scientists laying more than 1,500 camera traps and nearly 7,500 live traps at 300 sites in national parks, private conservation reserves and Indigenous-managed land.
Alyson Stobo-Wilson, an ecologist at Charles Darwin University who led the project, said the impact of feral livestock was found to be much greater than previously understood. The data from the traps, distributed across the NT using helicopters, suggested several once common mammal species were now found on offshore islands only, their mainland habitat having largely disappeared.
“We found the role of large feral herbivores in mammal declines, including feral cattle, horses and buffaloes, has been greatly underestimated,” Stobo-Wilson said. “They’re going rampant in a lot of places.”
The research found feral and farmed livestock trampled and overgrazed on the habitat and food sources of native mammals that weighed less than five kilograms. Stobo-Wilson said the overgrazing combined with damage from frequent large fires to leave native mammals more exposed to feral cats and dingoes.
The studies challenge suggestions that introducing more dingoes into a region may be a solution to reducing the impact of feral cats, finding they often live together in mostly open areas.
Instead, it would be better to protect habitat because areas with complex vegetation – such as the Tiwi Islands, Groote Eylandt in the Gulf of Carpentaria and the Cobourg Peninsula north-east of Darwin – were less likely to be overrun by cats and more likely to be rich in native species.
Graeme Gillespie, director of terrestrial ecosystems at the NT’s Department of Environment and Natural Resources, said: “This research adds to a growing body of work from northern Australia that indicates that across most of these landscapes better management of herbivores and fire, rather than culling cats, is likely a more effective way of protecting small mammals.”
