THE rats never stood a chance. It took a pair of feral cats just four days to gobble an entire population of native pale field rats in a conservation enclosure on the edge of Arnhem Land.
Scientists and ecologists have long suspected feral cats were partly to blame for the dramatic decline of native animals across northern Australia over the past 20 years. But preliminary results from a comprehensive study, funded by the Australian Research Council and led by the non-profit Australian Wildlife Conservancy, reveal just how devastating the predators can be.
''We had strong suspicions they were an issue, but we really needed to confirm that,'' said the conservancy's head scientist, Dr Sarah Legge.
On a former cattle station turned wildlife sanctuary, the conservancy has built two 10-hectare enclosures, each divided into two plots, to conduct their study.
One ''control'' plot allowed feral cats access in and out, while the second ''experimental'' plot was surrounded by a six-metre electrified fence to keep cats out.
Into each of the four plots, the group released about 20 pale field rats, which have been regionally extinct in Arnhem Land for about 15 years and had to be sourced from Quoin Island, off the Northern Territory coast.
''[Then] we followed their fate,'' said Dr Legge.
It took feral cats about a month to find one of the control plots. When the researchers tried trapping the rats, or locating them by their radio collars a week later they found none.
''Once the [cats] knew there was good feed in there, they were right into it,'' said senior wildlife ecologist Dr Katherine Tuft.
Motion sensor cameras had captured images of two cats, she said. ''Once they have decided there is something they like eating they put an awful lot of effort into getting the last rat,'' said Dr Legge. ''I think that's partly why they've been so devastating.'' she said.
While the rats in the second control plot survived better, the enclosure's first feral cat arrived in late October.
''So, we'll have to wait and see what its done,'' said Dr Tuft.
Both the plots that excluded cats now have thriving rat populations that have produced young. The numbers of reptiles have also increased.
While the preliminary results show the impact feral cats have on the small rodents, the researchers will also study whether the presence of cats prevents the recovery of the population.
The research team, which includes scientists from CSIRO, the University of Tasmania and Charles Darwin University, plan to run the experiment for another year, and may introduce other native animals to the cat-free plots.