Dingoes, rabbits & diseases

Contributed by: Dr. Brian Cooke (Sept, 2021)

A few years ago, it was in vogue to declare that dingoes were the unsung heroes of conservation in Australia. Advocates argued that having dingoes about suppressed cats and foxes, and hey presto, native animals could be expected to return to former habitats.

Some researchers even began to argue that, not only could dingoes suppress cats and foxes, but they also held rabbit numbers low. But what was the evidence for such a statement? If dingoes were highly efficient predators of rabbits, how did rabbits so easily become established throughout inland Australia in the first place? Furthermore, early pastoralists in the Strzelecki region, like the Ragless brothers who took up a lease in 1882, reported that it was only after rabbits arrived in 1888 that dingoes increased and began worrying their sheep. Rather than suppressing rabbits, did dingoes benefit from having over-abundant rabbits as a new food source?

Surprising as it may seem, there are many opinions but no serious research to determine whether dingoes are able to suppress rabbits. Certainly, rabbits, make up over 60% of dingo diet in many parts of inland Australia. However, rabbits also make up a high proportion of the diet of introduced feral cats and red foxes.

The best information we have for understanding whether predators suppress rabbits comes from studies carried out at Yathong Nature Reserve in western New South Wales where cats and foxes were experimentally culled from part of the study area and changes in rabbit abundance were recorded over many months before predators were allowed to return. An adjoining area where predators were not culled was used for comparison.

It turned out that, where predators were eliminated, rabbits increased to much higher levels than on the area where predators remained, but when predators were allowed to return, they were unable to reduce rabbit abundance again. Rabbits remained numerous until food shortage and excessive numbers caused the population to crash. The researchers considered that this was evidence that predators could keep rabbit populations low under some circumstances, yet in good seasons, or if there were too few predators, the rabbits could become so numerous that predation could no longer suppress them.

Prior to the introduction of rabbit haemorrhagic disease (RHD), first released in 1995, rabbit plagues were frequent on Quinyambie cattle station in the southern Strzelecki region. These plagues occurred every five to seven years, usually following good seasons, despite dingoes being common. These population irruptions were clear indications that rabbits were able to breed so efficiently that they produced more progeny than the dingoes could hunt and eat.

Putting all the details above together, we can safely conclude that rabbits on Quinyambie were not consistently limited by dingo predation. That was only likely if drought and associated food shortage temporally lowered rabbit productivity. Nonetheless, when RHD was introduced, it too reduced rabbit productivity by killing large numbers of sub-adult rabbits and this may have allowed predatory dingoes to play a more consistent role in keeping rabbits low. This might explain why researchers who have only studied the role of dingoes in the last couple of decades believe that dingo predation is so important. However, they err in failing to give credit to rabbit biocontrol as being critically important too.

Again, we don’t have direct experimental evidence, but interactions between foxes, disease and rabbits provide some supporting evidence. When European rabbit fleas were introduced into Australia as vectors of myxomatosis, they spread myxomatosis in the cold winter months rather than in summer when mosquitoes are active.

This meant that rabbits became infected with myxomatosis while young. Low temperatures further enhanced disease severity making the rabbits easier prey for predators and providing more carcases to scavenge.  Under those circumstances, foxes benefited, their numbers increased relative to rabbit abundance, and the rabbit population remained very low. Nonetheless, when severe drought killed the rabbit fleas on the study site, and myxomatosis reverted to normal mosquito-borne summer outbreaks, the rabbit population increased rapidly, and the ratio of foxes to rabbits fell.

The simplest explanation was that a combination of wintertime myxomatosis carried by rabbit fleas and predation had been highly effective in keeping rabbit abundance low. But, once rabbit numbers rose, predation was ineffectual in controlling their abundance. If there are similar interactions between RHD and dingoes, then dingoes could be adding to the effectiveness of RHD over much of inland Australia beyond the dingo fence, when RHD is active.

Overall, there is plenty of historic evidence to safely conclude that dingoes alone cannot prevent rabbits from reaching plague numbers and causing extreme ecological damage. In today’s degraded ecosystems, rabbits are by far the most common prey and consequently they are the major prey of many predators. More importantly, even if dingoes help to keep rabbit numbers down, even with RHD and predators combined, rabbits are seldom reduced below a level of about 0.5 rabbits per hectare which is a prerequisite for regeneration of many palatable native plant species.

It is a myth that dingoes alone could control rabbits well enough for ecological restoration and this needs to be dispelled. Unfortunately, one problem with today’s electronic media is that news which is controversial gets put up as headlines to attract readers attention, whereas useful basic research is rarely considered newsworthy. Hence, it seems controversial information, such as the idea that dingoes can suppress rabbits, stays on the world-wide-web forever, even if it is wrong. It pays to be cautious and always check that controversial opinions can be verified.

But, for now, the message is: Dingoes can’t suppress rabbits well enough to prevent continuing ecological damage.

Further reading

Cooke, B.D. (2019). Does red fox (Vulpes vulpes) predation of young rabbits (Oryctolagus cuniculus) enhance mortality from myxomatosis vectored by European rabbit fleas (Spilopsyllus cuniculi)? Biological Control, 138, https://doi.org/10.1016/j.biocontrol.2019.104068

Cooke, B. D., & Soriguer, R. C. (2017). Do dingoes protect Australia’s small mammal fauna from introduced mesopredators? Time to consider history and recent events. Food Webs12, 95-106. https://doi.org/10.1016/j.fooweb.2016.04.002

Corbett, L., & Newsome, A. (1987). The feeding ecology of the dingo. III. Dietary relationships with widely fluctuating prey populations in arid Australia: An hypothesis of alternation of predation. Oecologia, 74(2), 215-227. Retrieved July 21, 2021, from http://www.jstor.org/stable/4218457 

Pech, R.P., Sinclair, A.R.E., Newsome, A.E. et al. (1992). Limits to predator regulation of rabbits in Australia: evidence from predator-removal experiments. Oecologia 89, 102–112.

Featured image. Dingo in Simpson Desert. Source: Peter Day.

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