Australasian Science: Australia's authority on science since 1938

Know Your Enemy

Credit: Bernard Dupont

Credit: Bernard Dupont

By Lisa Anna Steindler & Mike Letnic

An ingenious experiment has tested whether shared evolutionary history enables bilbies to detect threats from dingoes but not feral cats.

The greater bilby once roamed far and wide across the Australian continent, and was found across 70% of the country. Sadly, since European settlement the bilby population has drastically declined, becoming concentrated and restricted to a mere 20% of their former range.

It is now more common for you to find an Easter bilby on the shelves of a supermarket than it is to see a bilby in the wild. The main reason for the drastic loss of this species, as well as many other native mammals, has been the introduction of exotic predators such as the red fox and feral cat.

The inability to recognise a predator and mount appropriate anti-predator responses is often dubbed “prey naïveté” and has been implicated in the decline of many Australian mammals, including the bilby. Previous studies have suggested that a species’ ability to recognise predators may depend on how long they have co-evolved with that predator. In species that have had a long-history of evolution with their predators, predator recognition may become hard-wired so that prey exhibit innate abilities to recognise and respond to the scents and images of co-evolved predators. In contrast, prey species that have not been exposed to predators over evolutionary timescales may learn through lifetime experience to recognise and respond to the scents and images of predators. What does this mean for the future of the bilby in the wild?

Our study, which was recently published in Animal Behaviour (https://goo.gl/SvJTB4), sought to discover whether bilbies could recognise and distinguish between the scents of two different predators with which they have shared varying timeframes of co-evolution. Bilbies have shared more than 3000 years of co-evolutionary history with dingoes but less than 200 years with cats.

Our understanding of the evolutionary timeframes necessary for prey species to maintain or acquire appropriate responses to introduced predators is poorly known. Knowledge of whether prey are responding to predators as a result of hard-wired instinct or lifetime experience is vital to understanding whether

re­introductions of threatened species, such as the bilby, is possible. If prey species can adequately recognise and appropriately respond to introduced predators such as cats, then it may no longer be necessary to classify these predators as introduced but instead naturalised and, as such, native species.

In order to test whether a bilby’s nose knows the difference between a predator that has been in Australia for thousands of years (the dingo) and a predator that has only been here for a few hundred years (the cat), we studied bilbies within a 60 km2 fenced exclosure at Arid Recovery Reserve in South Australia. A 1.8 metre-high predator-proof fence surrounds the reserve, with dingoes, foxes, cats and rabbits excluded from the fenced exclosures where the study was undertaken.

Since 2000 a population of greater bilbies has flourished within these predator-free fence exclosures. However, what are the consequences of living in an environment where there are no predators? Is it possible to have a future beyond the fence if you have never lived with a predator? Does the bilby’s nose know who is a predator and who is a friend?

To help answer these questions we caught 18 wild individual bilbies and tracked them to their burrows, where we challenged them with the scents of a predator with which they have had more than 3000 years of co-evolution, the dingo, and a more recently introduced predator, the feral cat, with which they have had at most 200 years of co-evolution. Bilbies were tracked through the use of radio transmitters and monitored at their burrows by infra-red motion sensor video cameras. Individuals were radio-tracked daily to their diurnal burrows for 2–8 weeks where we were able to conduct odour-recognition experiments.

Prey are able to detect and respond to the presence of predators through the use of sight, sound and smell. Prey animals such as bilbies use burrows as refuges from predators. Since predators can move through landscapes, the risk of predation outside burrows fluctuates through time. As a result, prey must decide when it is safe to move in and out of a refuge.

We placed faeces from two introduced predators (dog and cat), a herbivore (rabbit) and no odour at the entrance of the bilbies’ burrows, and observed the behavioural response of bilbies. The decision to emerge from a refuge, such as a burrow, requires prey to estimate the predation risk outside the shelter against the opportunity to find food and/or mates.

If the length of time that bilbies co-evolved with predators influenced their ability to respond to predator scents, we expected that bilbies would be more wary when emerging from burrows when dog faces were present. If, on the other hand, bilbies generalised their response to all predators, than we expected that bilbies would respond similarly to dogs and cats, but not respond to rabbits.

Our experiment showed that bilbies only spent more time partially emerged (with no more than their head and shoulders out) from their burrows when dog faeces were present compared with cat and rabbit faeces and the control. Despite their isolation from placental predators throughout their lifetime, bilbies at Arid Recovery Reserve appear to be able to respond to the odour cues of dingoes/dogs.

These results are consistent with the idea that the ability of a prey species to respond to the odours of predators scales with their period of co-existence. This suggests that in co-evolved predator–prey systems, prey may be able to innately recognise predators they have evolved with, in this case the dingo, but lack this recognition when a predator is novel, such as cats.

These findings imply that bilbies are naïve towards cats and that less than 200 years of evolutionary exposure is not enough for bilbies to develop and retain appropriate anti-predator responses to this species. On the other hand the bilby’s nose knows the smell of their long-term predator, the dingo.

Maybe it’s time we consider dingoes as native animals because bilbies recognise the scent of dingoes, but not cats.


Lisa Anna Steindler is a PhD student investigating native prey recognition of introduced predators in Australia through the School of Biological, Earth and Environmental Sciences at The University of NSW, where Mike Letnic is an Associate Professor researching the conservation, management and restoration of ecosystems, with a current focus on new approaches to improve the outcomes when reintroducing threatened species.