Know thy enemy - What happens when you breed animals in an environment where there are no predators?

Admin Aridrecovery - Tuesday, October 18, 2016

There have been a few blogs along the way regarding my research of the Greater Bilby (Macrotis lagotis) at Arid Recovery (refresh your mind here, here and here). But as they say all good things must come to an end. Time certainly does go too quickly when you are having fun doing field work at Arid Recovery, especially when you are working with unique animals like the bilby. Two and half years ago I embarked on an amazing adventure that took me all the way from the yellow sands of Bondi Beach, Sydney, to the red desert of Roxby Downs, South Australia. As soon as I heard that there was a PhD project investigating the prey naïveté of Australian native mammals, like the bilby, I knew I had to be a part of it!

Figure 1: The Greater Bilby Photo credit: Lisa Steindler

Prior to European settlement the bilby was found over 70% of Australia. Unfortunately, today they are considered legally extinct in the wild in South Australia, New South Wales and Victoria. The biggest identified threat and cause for this decline has been the introduction of exotic predators, such as the red fox and feral cat.

Thanks to the amazing work by organisations, such as Arid Recovery, feral free reserves have been established. The bilby population at Arid Recovery has boomed within this ‘safe haven’ for reintroduced species. But what happens when you breed animals in an environment where there are no predators? Do they lose all recognition of predators? Can we release them outside the fence where there ARE feral cats, red foxes and dingoes? Like many others we want to see Australian mammals beyond the fence and back in the wild and my PhD research is a step in that direction.

Now onto some basic theory behind that term “prey naïveté”, what exactly does it mean?!  If a prey animal is able to recognise a predator, they may be able to decrease their chances of being eaten. This is often known as an ‘anti-predator’ response. Whether a prey animal is able to recognise a predator may be influenced by their lifetime experiences. Animals may learn through personal experience whether another animal is a friend or an enemy who wants to eat them. Sometimes prey may not be exposed to predators within their lifetime, but they are still able to recognise and respond to them (i.e. in the case of animals living within the Arid Recovery Reserve). Animals that have lived with a particular predator for hundreds and even thousands of years may have “hard wired” responses to this predator. On the other hand, sometimes isolation from all predators over an animal’s lifetime or over hundreds to thousands of years can lead to the loss of all ‘anti-predator’ behaviours – “prey naïveté”.  

Understanding if prey are able to recognise and respond to a predator is important.

Theories on prey predator discrimination and recognition are divided as to whether prey species’ ability to recognise and avoid predators is proportionate to the duration of evolutionary exposure to specific predators or is a result of more generalised discrimination processes. Moreover, the understanding of the timeframes necessary for prey species to maintain or acquire appropriate responses to introduced predators is poorly understood. To be able to answer the question of how we can teach our native animals to be more aware of introduced predators we first need to understand what their current level of understanding is.

I attached radio transmitters to 18 bilbies at Arid Recovery so that each day I could radio-track sleeping bilbies to their burrows. Faecal samples from cats, dogs and rabbits were placed on the outside of bilby burrows to see how they would respond, as bilbies often use their strong sense of smell to recognise predators. Remote cameras were used to film the response of bilbies to the olfactory cue as they emerged from their burrow. The idea was that bilbies had to decide whether it was safe enough to exit the burrows when the faeces were present. If they recognised the faeces as a threat, then they should be more hesitant to leave the burrow compared to when they did not recognise it as a threat.

Figure 2: I radiotracked 18 bilbies for three months with the help of wonderful volunteers.                 Photo credit: Lisa Steindler

Figure 3: Camera traps were used to film bilby emergence behaviour. Photo credit: Lisa Steindler

Video analysis of burrow emergence behaviour determined that bilbies were indeed more hesitant to leave the burrow when certain predator scent was present. Bilbies spent more time only partially emerged (with at most head and shoulders out) as opposed to fully emerged (standing quadrupedally or bi-pedally, fully emerged from burrow) from their burrows when dog faeces were present, in comparison to faeces of cats, rabbits and an unscented control. The Greater Bilby has shared over 3000 years of co-evolutionary history with dogs but less than 200 years with cats. The ability of prey species to respond to the odours of predators relates to their period of coexistence. The longer that you have known your predator over evolutionary time may influence whether you can recognise their odour, even if you aren’t currently living with them.

Figure 4 and 5: What was classified as a partially emerged bilby vs a fully emerged bilby.            Photo credit: Lisa Steindler

This research is only the starting point to seeing a future for bilbies beyond the fence. This research would suggest that despite at least 15 years of isolation from placental predators, bilbies retain some level of “hard wired” recognition of their historical predators (dingoes). The next question will be: Can they survive predation attempts by these predators? Can we teach them to be a bit more aware of introduced predators such as cats and foxes? And can adapt to live in a changing world outside the fence where these predators now exist?

Thanks to all the wonderful support from my supervisors, Arid Recovery staff, and volunteers along the way, I have had an amazing PhD journey that has led to many moments of blood, sweat and tears, a growing family of wonderful friends and precious memories of a unique, charismatic animal ... the bilby!!

Written by Lisa Steindler, PhD candidate with the UNSW. 

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