Imma Perfetto
Cosmos science journalist
Move over Easter bunny, the greater bilby bounced back in some places in Australia this year.
According to fifth Annual Bilby Census at the Australian Wildlife Conservancy (AWC) reserves, populations of the iconic Australian marsupial have been booming.
They now total an estimated 3,330 individuals in 6 populations which are all protected by large, feral predator-proof fences within AWF sanctuaries in Western Australia, the Northern Territory, South Australia and New South Wales.
It’s a positive trend echoed in other feral-proof fenced reserves.
According to Dr Lauren Young, Chief Executive of South Australia’s Arid Recovery, their annual trapping count will begin in May but initial counts taken in the past 2 weeks indicate that the bilby population within the reserve remains stable. And, with a number of babies and juveniles spotted, the bilbies appear to have had a good recent breeding season.
AWC Senior Ecologist Dr Jennifer Anson told Cosmos that the results of their Annual Bilby Census demonstrates that conservation work is having a real impact for bilby populations.
“Bilbies used to be across about three quarters of Australia, and they’ve now disappeared from about 80% of their former distribution,” says Anson.
The ones left in the wild are found only in small, discrete populations in the NT, WA, central Australia and Queensland. They are listed as Vulnerable under the EPBC Act.
“They’re all under threat from those same drivers that have led to [the] widespread collapse of the species,” she adds. Feral predators – such as cats and foxes – are the main culprit, alongside habitat degradation and changes to fire regimes.
But predator-free sanctuaries provide safe and healthy habitats for the species to thrive.
“Four of these populations are actually relatively new … reintroduced in the last 10 years, some of them in the last 5 years,” says Anson.
“These are into some of the larger safe havens in Australia … We know that these populations haven’t reached the carrying capacity, they haven’t reached the limit yet, and they’re continuing to expand and use all the available habitat that there is within those safe havens.”
But while not all of the bilby populations experienced a boom, Anson is confident the populations will rebound.
“These kinds of arid-adapted species … they’re able to breed quite quickly and build up their populations when conditions are good,” she says.
“With boom-bust species, we would always expect those individual populations to increase and decrease depending on the environmental conditions at the site.”
A 2.5-year drought dried the landscape and caused a shortage of food resources which ultimately impacted the reintroduced bilbies inside Mt Gibson Wildlife Sanctuary on Badimia Country in WA.
The population estimate reduced from 1,770 individuals in February 2023 to 986 individuals in November 2024.
“The majority of these safe havens are large, it means that the populations within them also have the ability to be quite large, and so they’re a bit more resilient to that environmental change,” says Anson.
“They’re less reliant on genetic management to be remain viable over the long-term. So even though we get that fluctuation, we expect the population to remain healthy, rebound and keep growing.”
These populations have been restored to sanctuaries in locations from one end of their former range to the other. This has been done, in part, to increase the bilby’s “adaptive potential” to ensure they can cope with Australia’s changing climate.
“It exposes the bilby genome to different environmental selective pressures, and this makes them a little bit more resistant to a change in climate,” says Anson.
Heatwaves are becoming hotter, longer, and more frequent in Australia’s arid outback. How the bilby is coping with this increasing heat stress isn’t well known due to their cryptic nature as nocturnal burrowers.
In separate research, a PhD student at the University of New South Wales, Jack Bilby (yes, his real name), and the team from the Arid Recovery are trying to figure it out.
They aim to study, using a combination of lightweight devices to track their movements, behaviours, and experience of temperature and humidity, how the greater bilby responds to extreme heat.
They’ll then compare this with data captured on another arid-zone burrower: the invasive European rabbit.
Ultimately, the aspiration is to re-establish bilbies in the wild across large parts of their former range, so that the precious eggs aren’t in just a handful of baskets.
“By having this geographical spread of these populations across the former range, it can also limit the impact of a single catastrophic event, such as wildfire or the recent flood events,” says Anson.
“They’re an incredibly charismatic, iconic species. They’re really, really important to ecosystems – they’re an ecosystem engineer.
“So having these animals in the landscape is not only good for bilby conservation, but also to maintain these healthy landscapes across Australia as well.”
