Feral cats cutting a swathe through wildlife?

Feral cat caught on camera with a vulnerable native species – the phascogale. (Credit: Marika Maxwell, Invasive Animals CRC)

How many feral cats are there in Australia? That is the big unknown according to a research study from the Invasive Animals Cooperative Research Centre and the University of Canberra’s Institute for Applied Ecology which states that the numbers of feral cats, feral pigs and red kangaroos across Australia is unknown and there has been a bias towards citing large numbers that lack the scientific evidence to back them up.

Co-author of the scientific review, Dr Tony Buckmaster, said, “You hear the number of feral cats in Australia reported as being anywhere up to 18 million. The truth is we just don’t know how many there are. We think that the figures currently used are from someone just multiplying the feral cat density estimates from one study in northwest Victoria in 1982 by the total landmass of Australia. Our research shows that we lack the reliable scientific knowledge to give current estimates of feral cat abundance at a continental scale. We have better knowledge for feral pig and red kangaroo abundance but that is also dated.”

“People get hung up on the numbers game. Unless needed for an eradication program or commercial purposes, knowing the exact numbers of these animals in the landscape is not really important. It is much more useful to focus on the damage caused.”

Other factors, such as weather, mean the populations of these animals are always highly variable so abundance changes considerably over time.

“Abundance data from two or more decades ago really does not apply today,” he said.

The review argues that there appears to be a bias towards citing large numbers rather than reporting the estimate and the range. It becomes a type of ‘citation creep’. This stating of inflated feral cat numbers does not occur usually in scientific journals. An analysis of the scientific journal Wildlife Research over a thirty year period did not find a single paper stating an estimate of the population size of feral cats at a continental level.

“Talking about 18 million feral cats seems to be based on little more than a guess, rather than the scientific evidence available,” said Dr Buckmaster.

“Since numbers are often used for planning wildlife management programs for many species, it is important to evaluate the evidence and reliability of the available data, rather than doing guesswork. We need reliable, robust data and good science with strong evidence to get a more accurate picture,” said co-author Professor Jim Hone.

The research report ‘How many are there? The use and misuse of continental-scale wildlife abundance estimates’ (http://www.publish.csiro.au/?paper=WR14059) by Professor Jim Hone from the University of Canberra’s Institute for Applied Ecology and Dr Tony Buckmaster from the Invasive Animals Cooperative Research Centre is published in the journal Wildlife Research.