Breaking the boom-and-bust cycle of the Astrebla Downs greater bilby population
Astrebla Downs National Park is a remote and arid expanse in western Queensland renowned for its treeless Mitchell grass plains, red earth and rugged beauty. It is also home to several threatened species, including the greater bilby, kowari and the plains wanderer. The park plays such a crucial role in their conservation that it is not open to the public.
The greater bilby once ranged over most of mainland Australia. However, the introduction of predators, such as feral cats, red foxes and wild dogs, has led to a significant decline in the species.
The greater bilby population at Astrebla Downs is the most significant wild population remaining in Queensland, but its future is far from certain, as conservation officer Maree Rich explained.
“Over the years, we have witnessed a boom-and-bust cycle in the bilby population,” Ms Rich said. “As few as 200 greater bilbies lived at Astrebla Downs in 2014 after feral cats devastated their stronghold in Queensland.
“In contrast, in 2021, when we conducted surveys, we had never seen so many bilbies in the park. More recent surveys indicate that the population has declined again since 2021.
“When predation outstrips the bilbies’ reproductive rate, bilby populations can decline to very low numbers. We think that a good season, followed by lots of little bits of rain, encourages more and more native long-haired rats, increasing the breeding success of feral cats and wild dogs that prey on bilbies. At the peak of the cycle, predator numbers are hyper-inflated, and when the numbers of long-haired rats start to decline, predators can switch from eating long-haired rats to other food sources like bilbies in just a few weeks.
“When conditions are consistently dry, however, predator numbers drop, and the bilby population can do well because bilbies are arid specialists. When there’s very little rain, they can thrive when other species may not.”
The team are trying to better understand the sweet spot for the bilby’s recovery, and the boom-and-bust cycle needs further research. In the meantime, they focus on regular monitoring of the bilby population at Astrebla Downs and controlling bilby predators.
They use thermal monitoring equipment, drones, fixed-wing aircraft and acoustic recorders to monitor the threatened species populations in the park.
Due to the park’s remote location and its challenging conditions, each trip requires careful planning and preparation. The team makes 4–5 control trips per year, depending on the abundance of pest animals.
Feral cat and wild dog control at the park has been critical to conservation efforts since 2012. The team uses specialised baiting strategies that minimise the risk to non-target species and high-tech thermal scopes to improve the humaneness and effectiveness of the control work. Ongoing research and collaboration with wildlife conservation groups help refine the control methods and improve outcomes for the greater bilby.
Since the bilby conservation program began, the team has removed more than 3,400 feral cats and 140 wild dogs. Post-mortem examinations of the pest animals reveal information about their genetic makeup, ecology and diet that informs future control activities.
The monitoring and predator control programs can be challenging for the team, with freezing nights in winter and searing heat in summer at the park. Their reward is seeing the bilbies persist, continuing their ecosystem engineer role well into the future.