Junk science being peddled in Tasmanian cat management debate

When groups come out with outrageous claims about cat populations, they will usually remain unchallenged. Partly because there seems to be a pervasive belief that the ends (generally cat laws or some other restriction on ownership), justifies the means (overwhelming exaggeration and fundamental errors and inflations in cat population estimates). Or simply that the data doesn’t exist. Or the data that does exist is so flimsy, that it is very hard to use it to rebut assertions by otherwise reputable groups.

Sometimes these claims have been deliberately created simply to disrupt methodical and scientific debate about cat management programs. And they have been designed to be so ‘catchy’ that they have the potential to become the new ‘go-to’ stat for media and anti-cat advocates. That is what we are dealing with here.

The Tamar Natural Resource Management Group (NRM), says it is time to tackle the growing feral cat population.

The group estimates there could be as many as 1.2 million roaming Tasmania.

This figure is based on the State of the Environment Report in 2009, which stated the estimated cat population was about 150,000.

However anecdotal reports had indicated the population could have doubled between 2005 and 2007.

Tamar NRM president Ian Sauer said the population was still likely to be increasing rapidly.

“To put this into context, a feral cat eats approximately three animals a day,” Mr Sauer said.

“With 1.2 million cats in Tasmania, this equates to 3.6 million small animals, lizards, and birds taken out of Tasmania’s ecosystem every day.”

Startling yes?

That 1.2 million feral cats in Tasmania has a disturbing ‘ring’ to it – one that 150,000 simply can’t match. And now it has been published in the state’s major newspaper – the Mercury – it is likely to become the figure those supporting a widespread cat-cull will start to use in their communications. So let’s take a look at it.

 

First up, let’s just take a moment to look at Mr Sauer’s maths.

The Tasmanian ‘State of the Environment Report’ 2009, does indeed state;

It is estimated that the feral cat population may be as high as 150,000 and may have doubled in the two years from 2005 to 2007 .

If between 2005 and 2007 the population of feral cats doubled – the original number of cats in 2005 was about 75,000.

And if every two years the population continued to double, by today in 2013, we would see the 1.2 million cats as speculated.

 

So I can replicate his calculations, which is a start.

However, without more extensive statistics (was the population of cats going up or down prior to this number? Was the ‘doubling’ an anomaly or part of a wider trajectory of huge exponential increases?) to predict that, that level of growth – a massive population explosion – would be maintained into the future is simply, speculation based on a very small amount of data.

Not always totally wrong, but rarely accurate either.

 

So, where did this ‘doubling’ number come from?

The reference documents for the ‘State of the Environment Report’ direct us to;

Hocking, G. 2008, Spotlight surveys, unpublished data provided by DPIW, Hobart.

 

What is a spotlight survey?

It’s some researchers with lights, looking for animals at night.

In the case of the actual full report, the researchers were ‘spotlighting’ for native animals (Tasmanian Devils, Spotted Tailed Quoll, Eastern Quoll, Forester Kangaroo, Tasmanian Betting, Eastern Barred Bandicoot, Southern Brown Bandicoot, Common Wombat, Ringtail Possum, Long-nosed Potoroo) and as an aside, they recorded non-native animals (Fallow Deer, Feral Cat, and Rabbit).

– In 2005, 33 feral cats were spotted on mainland Tasmania, three on Flinders Island and five on King Island (41 total)

– In 2007, 28 feral cats were spotted on mainland Tasmania, eight on Flinders Island and zero on King Island (36 total)

Making the conclusion that feral cat numbers had ‘doubled’ incorrect.

There is even a graph on the ‘State of the Environment Report website which showed cats (the blue line) hadn’t doubled, but had fluctuated during those two years, as would be expected in a relatively stable population.

 

So does 20 – 30 individual cats equate to more than a million?

Of course not.

The extrapolation by Tamar NRM of the data – a few dozen animals seen on a survey not even designed to count cats – to a population explosion of more than a million animals, is absurd and deliberately misleading.

There is no basis for the Tamar NRM assertion that cat numbers are spiking, or have increased from the original estimate of 150,000, based on the evidence they have presented.

The ‘doubling’ comment from the original report needed to be taken in a wider context, not used as a blunt instrument for an erratic attack on cats. Extrapolating data from small, isolated studies to draw conclusions about cat populations in wider urban and rural environments, is junk science at best. And dangerous at worst, as these figures are being used to drive the government towards cat culls.

Tamar NRM was calling on the State Government to take a strategic approach to feral cat management.

The strategy should include a national approach to management and the identification of high conservation areas that may need an immediate cat cull.

“A disaster is not waiting to happen, it is happening,” Mr Sauer said.

“Feral cats have now spread to every corner of Tasmania and, indeed, Australia. Sadly State Parliament was informed recently the Government no longer knows how many feral cats there are in the state.”

 

At least the government is being honest about the lack of data around cat populations, rather than pulling figures out of their proverbial, which is more than can be said for Mr Sauer. This is easily the worst bit of cat-bashing junk science I’ve ever seen delivered in the public space and can only be described as absolutely revolting.

However, this could very well be a successful PR campaign against the cat, and I fear we will see the 1.2 million cats slogan being used as ‘fact’ in future debate.