At the Threatened Species Summit last week in Melbourne, Environment Minister Greg Hunt and Threatened Species Commissioner Gregory Andrews declared war on feral cats.
Cats are thought to be a significant contributor to the decline of many threatened species.
Targets in the released threatened species strategy include culling two million cats by 2020, creating new safe havens for threatened species (cat-free islands and sanctuaries), restoring habitat and emergency intervention for our most critically endangered species.
Excluding cats using fencing is an increasingly important tool used to protect threatened species. New exclusion fencing projects received significant funding under the latest strategy.
One of us (Katherine) was lucky enough to be asked to give a presentation at the summit on alternative methods of controlling feral cats. The following article summarises this presentation and highlights the importance of investing in a broad range of cat control methods.
Cats are highly adaptable and highly variable, hence we must continue to search for their Achilles Heel and invest in a wide range of control methods.
Widespread poison baiting for cats has come a long way in the last few decades with baits such as Eradicat, Curiosity and a new hybrid Eradicat bait being produced.
These baits were developed after years of research conducted initially by the WA Department of Parks and Wildlife and are a soft meat sausage injected with 1080 poison or containing an encapsulated PAPP (Para-aminopropiophenone) pill. These baits have had most success in island eradications and areas where alternative prey are scarce.
In order to kill a cat using poison baits, cats must first find and then ingest the bait.
Unfortunately, cats hunt mainly using sight and sound so finding an inert sausage is a challenge for a cat.
Large numbers of baits must be laid, the usual density is 50 per square km, 10 times higher than the recommended fox baiting density of 5 per square km.
Despite this, many cats fail to find a poison bait before they break down and are no longer toxic. Even when cats do find baits, up to 80% of encounters do not lead to bait ingestion, with cats often ignoring, sniffing or avoiding baits when detected. This is because cats prefer to catch their own prey and will only ingest a bait when hungry.
Non-target uptake can also be high – species such as crows, goannas and quolls can take more than half of laid baits in some instances.
Successful baiting relies on using large densities of baits in areas with low food availability at the right time of year when cats are hungriest. Practitioners are continuing to develop ways of improving bait uptake and several important baiting programs received funding under the Threatened Species Strategy.
A recent invention removes the need for cats to be hungry to ingest poison. An automated grooming trap squirts a poisonous paste onto the fur of the cat as it walks past a trap station, which it then ingests through compulsive grooming.
Cats are fastidious groomers and pen trials have found 9 out of 10 cats will ingest the paste when it is squirted on their fur. The trap uses an array of sensors to restrict triggering to target species and is currently being developed for field trials around Australia. The grooming traps have a silent activation, can store up to 20 doses and can sit unattended for months at a time.
Although unlikely to be used in broadscale applications, the grooming trap may be critical for protecting small threatened species populations and reducing the impacts of cats in areas where food availability is high.
The grooming trap received much needed funding for further development at the Threatened Species Summit.
Get rid of rabbits, get rid of cats
Widespread indirect methods of reducing cat impacts are also important. Recent work has found that the Rabbit Haemorrhagic Virus Disease (RHVD) (otherwise known as Rabbit Calicivirus) released in 1995 has had a significant positive impact on many desert threatened mammal species.
The range of species such as the Plains Mouse, Dusky Hopping Mouse and Crest-tailed Mulgara has increased by as much as 70 fold in the last 20 years due largely to reduced predation.
RHDV reduced rabbit abundance by up to 95% in the arid zone of Australia which resulted in a natural steep decline in feral cats and foxes, the main predator of rabbits in that region.
The increase in vegetation cover coupled with a massive decline in predation pressure has allowed these native rodents and marsupials to recover.
This would undoubtedly be one of the most significant recoveries of threatened species in Australia. RHVD was relatively cheap, for an initial investment of only $12 million. The agricultural benefit alone totalled more than A$6 billion and the benefits to threatened species have been dramatic but remain unquantified.
Other researchers have also found that by manipulating fire and stock grazing pressure, broadscale indirect benefits can be achieved for threatened species through a reduction in susceptibility to cat predation.
These indirect benefits include making it more difficult for cats to hunt by increasing ground cover, and increasing the productivity of the landscape thereby allowing native species to increase their reproductive output and tolerate higher predation pressure.
All cats are not created equal and recent work in the Flinders Ranges National Park has highlighted the impact of catastrophic cats on reintroduction programs. The reintroduction of the western quoll resulted in nearly a third of the quolls being killed by feral cats.
Melissa Jensen, Author provided
DNA analysis indicated that quolls were killed by large male cats with most cats responsible for multiple kills (Moseby, Peacock and Read,in press,Biological Conservation). These specialist hunters could be targeted by making their prey toxic, in other words employing toxic Trojans (poison capsules implanted under the skin of prey species where they remain stable) to control specialist cats.
Poison capsules can be implanted under the skin of prey species where they remain stable. If a cat kills and ingests a toxic Trojan, the capsule will break down in the acidic environment of the cat’s stomach releasing the poison and preventing it from killing more individuals. Research is continuing into this poison delivery device which may result in improved targeted cat control.
Finally, an ARC linkage grant between the University of New South Wales and Arid Recovery is researching ways to improve the anti-predator behaviour of threatened species.
Our native species did not evolve with introduced cats and foxes and hence may exhibit inappropriate or ineffective anti-predator responses. This prey naivety can lead to high susceptibility even to low levels of exotic predators.
Containing our threatened species on off-shore islands or behind fences is potentially exacerbating the issue as they are not exposed to mammalian predators and can develop “island syndrome” where they fail to recognise predators as dangerous.
The project involves trialling “in situ” predator training where low levels of predators are added to populations of threatened species for extended periods to improve their anti-predator behaviour.
The theory is that natural selection and learning will lead to improved survival and behaviour of successive generations of threatened species.
Whilst this may be a long term endeavour, ways of facilitating co-existence and increasing the resilience of our native species to exotic predators are urgently needed as it is likely that the wily feral cat is here to stay.
The authors would like to acknowledge the following for contributions. Poison Baits – Dave Algar, Michael Johnston, Keith Morris; Grooming traps- Invasive Animals CRC; Broadscale indirect methods – Reece Pedler, Peter Bird, Rob Brandle Rick Southgate, Rachel Paltridge, Sarah Legge; Specialist Hunters – Dave Peacock; Improving Prey Responses – Mike Letnic, Dan Blumstein, Bec West. Ecological Horizons has received funding from Sporting Shooters, FAME, Bush Heritage and SA and Australian Govt for development of Feral Cat Grooming Traps.