Richard Musgrove
Feral cats have been implicated in the deaths of reintroduced native mammals at two conservation sites in South Australia.
Such predation can often mean failure for translocation programmes, say lead author, Dr Ned Ryan-Schofield of the University of Adelaide.
Feral cats, house cats gone wild, kill an estimated 815 million animals each year throughout the Australian bush, 56% (456 million) of which are native species.
Bush dining is al fresco, without human waiters, the menu including 400 species of native vertebrates— 58 marsupial species, 123 birds, 157 reptiles, 27 rodents, 5 bats and 21 frogs.
These are underestimates because they don’t include animals killed but not eaten by cats or those that are maimed, then escape and die later of their wounds, says Professor John Woinarski, Professor of Terrestrial Ecology at Charles Darwin University.
Working out exactly what caused a death can difficult out in the bush, says coauthor Professor Katherine Moseby, of UNSW, who led Adelaide University and UNSW researchers to ask what else field data could reveal about the extent of cat predation. The results are in Australian Mammalogy from CSIRO Publishing.
“In past releases, we’d be radio tracking animals after release, and if we found dead animals, it would be difficult to determine what caused their death. We would use field evidence like animal spoor, carcass remains, or bite marks on collars to guess whether it was feral cats, birds of prey, fox, or if they just died a natural death.
“And because we’re working in really remote areas, it is difficult to access vets for necropsy. So taking a DNA swab of the dead animal was a really good way to identify if predation was the cause of death. And then we decided to compare the DNA outcomes with evidence in the field to determine if the latter was a reliable method of determining cause of death.”
The researchers analysed DNA extracted from confirmed and suspected cat kills, using data from four native species translocated in remote South Australia.
110 western quolls and 148 brushtail possums had been translocated to Ikara-Flinders Ranges National Park (IFRNP), a 93,812ha unfenced semi-arid conservation reserve, 400km north of Adelaide between 2014 and 2016. Quolls are nationally threatened carnivores, sheltering in hollow logs, burrows and rock crevices. Possums are mostly tree-living and shelter in tree hollows. Both are nocturnal.
89 burrowing bettongs and 42 greater bilbies were translocated to Arid Recovery, a 123 km2 conservation reserve, also in the arid north of South Australia, in 2000-2001. Both are also nocturnal — bettongs live in communal warrens, bilbies are solitary burrowers.
Of the releases at both sites, 74 of the 389 animals were subsequently killed by cats, 71 of those confirmed with DNA analysis, says Ryan-Schofield. 6 more cat-kills were confirmed by vet post-mortem, 5 of those also containing cat DNA.
Cats were also seen at 3 fresh kills, but only 2 returned positive cat-DNA tests — showing that even DNA was underestimating kills, says Ryan-Schofield.
The bettongs are gone now — no match for cats — but the other three species survive.
”The DNA is good, but it’s not infallible, and a lot of that is because we’re trying to get DNA from cat saliva found on the carcass, and that’s quite difficult because DNA degrades quickly in the environment,” says Moseby.
“But ultimately it highlighted that there are a lot more cat killings than previously thought.”
Field evidence alone is not enough to confirm cat predation; tools such as DNA analysis and necropsy are needed for confirmation, says Ryan-Schofield. We are still a long way off effective feral cat control in the Australian outback, he adds.
“Until we develop genetic tools or other broadscale methods targeted at feral cats, we can only rely on intensely managing them as best we can. We hope that this research might encourage more conservationists to use DNA and necropsy to identify the cause of death of animals in wildlife reintroductions, and to increase cat control even if no obvious evidence of cat predation are present,” Moseby says.
