Bilbies could hop back into mild climate zones: study

UNSW Sydney

Bilbies bred in a sanctuary in Dubbo have provided researchers with vital clues about how they would fare in temperate Australia where they once thrived.

A study of greater bilbies at Taronga Western Plains Zoo has provided some new ideas about how bilbies would cope if reintroduced to temperate areas of Australia where they once roamed.

Today the bilby is a threatened native marsupial that is restricted to areas where introduced predators are excluded or intensively managed. The beloved animal, often referred to as Australia’s answer to the Easter Bunny, has not lived within the temperate zone of their former range – southeastern and southwestern Australia – for more than 100 years.

Since European settlement, bilbies have experienced a massive decline in range due to competition with invasive rabbits and predation by feral predators such as cats and foxes.

And now scientists from UNSW Sydney and Taronga Conservation Society Australia have used a large sanctuary at Taronga Western Plains Zoo in Dubbo – part of the temperate zone in Australia – to better understand their habitat requirements in this part of the country.

Dr Kate Cornelsen was lead author in a study published today in the journal Animal Behaviour that detailed how greater bilbies responded to a temperate environment. Her PhD research in the Centre for Ecosystem Science at UNSW focused on understanding the habitat preferences and movement patterns of these unique nocturnal marsupials in the Sanctuary in Dubbo, where bilbies are being bred to release into the wild. She says up until now, very little is known about what bilbies do and need in the temperate zone.

“If bilbies are to be restored in the temperate zone where they once thrived, we need to know much more about where they like to go and what they need there,” she says.

“We fitted tiny GPS tracking devices to the tails of 20 greater bilbies, which recorded where the bilbies were every hour, giving us a unique insight into their nocturnal habits and preferences in this area.”

Mystery unravels

The detailed movements and behaviour of wild bilbies has been thought somewhat mysterious, so any light shed on this is novel. Andrew Elphinstone, Conservation, Recovery and Restoration Programs Manager at Taronga Conservation Society Australia and a co-author on the study says bilbies are important ecosystem engineers.

“Bilbies turn over and aerate the earth which improves soil health,” he says.

“Understanding the habitat preferences and needs of bilbies is critical to restoring the species to a wider area so that they can have a positive impact over as wide an area as possible.”

The research also uncovered some interesting patterns.

“Food biomass or availability essentially had a strong influence on where they preferred to hang out,” Dr Cornelsen says.

“They seemed pretty good at working out where the food was. Interestingly though, they also preferred certain soil types, and females were much pickier in this respect than were males.”

Female bilbies do all of the parental care, carrying young in pouches before stashing them in breeding burrows while they go out each night to forage. It seems that females must make a trade-off between burrowing in soft sandy soil that is easy to dig through and make a home in, versus basing themselves in more silty soil that is likely to have more food in it – but carries a flood risk as this soil type tends to be close to water.

“What’s interesting about this is that it shows the diversity of soil types bilbies can exploit – they’re not just limited to sandy soils good for burrowing,” says Dr Cornelsen.

Unsurprisingly, females tended to be more sensitive to the location and seasonal availability of resources than males, but males who didn’t need to return to breeding burrows were freer to select high quality feeding areas. Invertebrates (for example, beetles, termites, crickets and larvae) are a high-quality food resource for bilbies, and in seasons when they were abundant, males were less likely than females to use invertebrate hotspots.

Surprising find

In general, bilbies spent more time in areas further from water sources in most seasons. This was a little surprising to the researchers, as areas close to water are likely to be more productive and have more food available. However, in the temperate zone where this study took place, food might not be so limiting to the bilbies.

“Food is probably less patchy and more predictable in this study area compared to the desert where they’ve been studied before,” Dr Cornelsen says.

“Areas further from water probably still provide sufficient food for bilbies, and because bilbies get all of the water they need from their food, being further from water might help them avoid competition with other species that do need to drink.”

Dr Cornelsen says this demonstrates how the environmental conditions can change what is important.

“If we only study a species in one environmental context, we only have a small part of the story on what they actually need to thrive. Limited data means a limit to what we can infer about the type of environments in which a species can be reintroduced successfully for conservation.

“For future bilby reintroductions, we will now have greater confidence in the resources required by the species within temperate regions.”

By digging deeper into the preferences and movements of bilbies, this study has produced novel insights into how bilbies select resources, and makes a valuable contribution to their conservation.

/Public Release.