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CSIRO independent analysis: no support for kangaroo research assumptions

 by Maria Taylor - 18/10/2017


Special Bulletin investigation

In May of this year, we were confronted  by the eighth year (longer, if one counts killings going back to Googong in 2004) of ACT government contract killings of Eastern Grey kangaroo families on urban nature reserves – based on some mathematical formula for one kangaroo per hectare, or less, ‘to save biodiversity’ according to the official line. (Mothers Day Killings Start Again, District Bulletin June 2017, p11; Another unnecessary roo slaughter, Canberra Times, May 25 2017, p19).

This lethal program is on top of tens of thousands of kangaroos killed per decade with government license on nearby grazing leases and ditto in surrounding NSW.  In NSW too, a government-sanctioned multi-million dollar commercial petfood and leather industry kills hundreds of thousands more annually. (It is hardly surprising that kangaroos take sanctuary from bullets in more populated areas).

No relationship between commonly-found kangaroo numbers per hectare and ground cover condition in native grass and woodlands.

Whether it’s on grazing properties or Canberra’s grassy reserves, the kangaroos’ alleged sin is, simply put, that they eat grass. (The Eastern Grey is one of Australia’s remaining indigenous grazers that survived bounties and other colonial slaughters – and one of the few marsupials able to adjust to living with the humans now on their former habitat).

The ACT government since 2009 has not responded to requests for evidence showing the impacts or benefit of their kangaroo management program – that costs up to half a million dollars in taxpayer money every year.

Freedom of Information request finally yields some answers

Following this year’s urban ‘cull’ I filed a Freedom of Information request asking for the outcomes of kangaroo culling on flora and fauna in the Canberra Nature Park in recent years. I asked also for evidence of sustainable kangaroo populations and the basis for the one kangaroo/hectare goal.

I received an interesting batch of papers. They did not prove the ACT needs one kangaroo per hectare or less, or that this lethal management is sustainable.

They did show that the territory’s research and monitoring, such as it has been, can’t support the assumptions that preface their research and that also lead the public narrative – namely, that ACT kangaroo populations need to be “actively managed” to alleviate their grazing pressure.

The ACT Environment and Sustainable Development Directorate research wants to measure this grazing pressure by a simple correlation of kangaroo numbers and grass height, colour, density and bulk, what they call “green herbage mass”.

ACT research: measuring grass height and bulk as main data, plant diversity, animal interactions, or impact of the weather, not included.

A 2013 interim directorate report of how they research this relationship is prefaced with the assumption that pops up on each report: paraphrased it reads ‘everyone knows kangaroos damage the environment and we have to cut the density’.

Unfortunately there is no comparative baseline data on ecological communities that are allegedly damaged – either before the kangaroo management plan of 2010 or before a revised version was accepted in 2017.

CSIRO commissioned report no backing for ACT assumptions

Unfortunately too for the ACT position, a commissioned 2014 CSIRO report takes a fresh look from the outside – a perspective rebuffed during three ACT Administrative Tribunal legal appeals since 2010. This report covers the government’s data collection from 2009, 2012 and 2013. (Author Lyndsey Vivian is a consulting ecologist and botanist, and author Robert Godfree is a field ecologist specialising in native plant ecosystems).

The CSIRO analysis does not support the assumptions adopted by the parks bureaucracy in its kangaroo research and methods.

Instead it starts by asking an assumption-free scientific question: whether relationships exist between kangaroo density and vegetation condition in the Canberra grasslands and grassy woodlands.

What the CSIRO report found

There are three key findings that contradict the government’s narrative. The CSIRO report “could not identify any upper limit of kangaroo density beyond which vegetation richness, diversity and overall condition declines”. In other words, the authors checked ACT- studied sites with densities up to three kangaroos per hectare, and could not say that vegetation indicators had declined on any front up to that number of animals.

In regard to the one kangaroo or less per hectare goal, Godfree and his colleague also found no evidence. They could not “identify an optimal kangaroo density that maximises richness, diversity and condition”.

Thirdly, this study supported many criticisms about the lack of variables studied by the ACT, particularly the weather. “At the site level, changes in vegetation structure and composition varied more between years, which may be associated with different prevailing climatic conditions, than with kangaroo densities.”

It also notes other variables that can affect a site’s vegetation structure such as grazing history, previous fire and drought, soil conditions and nutrients, etc. “The low correlation between kangaroo densities and vegetation condition metrics is likely due to the variable nature of grassy ecosystem condition relative to a number current and historical site factors not related to kangaroo densities,” says this report.

So we have a CSIRO finding that ACT data up to 2013 yield no evidence of a measurable relationship between kangaroo grazing (up to averaged 3 per hectare) and the condition of on-ground vegetation. (One should add that these sites don’t have the additional pressure of simultaneous sheep, cattle or horses).

Undaunted, an ACT January 2015 project design report (harking back to research started in 2012) again claims that “the ecology behind the policy to control kangaroo grazing pressure is well understood”. It does admit that they don’t know a numerical relationship between kangaroo numbers and “green herbage mass”.

Photo caption admits something different

Looking for evidence of a negative relationship, the ACT research I saw never looked at the positive ecological relationship between kangaroos and grassland and woodland animals they evolved with.

So it was interesting to read as a caption for a report photo: “Eastern Grey kangaroos are magnificent animals, well-adapted to temperate south-eastern Australia, where their populations play a central role in the ecology of grassy ecosystems by altering the habitat of small plants and animals.” Perhaps they meant ‘by maintaining the habitat’.

My thanks for assistance with the FOI documents to ex CSIRO plant biologist Bill Taylor and Frankie Seymour former public sector social scientist analysing government environmental reports and policy.

Sources: Lyndsey Vivian and Robert Godfree: Relationship between vegetation condition and kangaroo density in lowland grassy ecosystems of the northern Australian Capital Territory,   2014 CSIRO report to the ACT Environment and Sustainable Development Directorate (EDP).

Rob Armstrong: Interim Analysis of relationship between vegetation condition and kangaroo density in grassy ecosystems of the northern ACT, Analysis of data collected in Spring-Summer 2009-2012,   2013 Environment and Sustainable Development Directorate (ACT Government)

ACT staff unnamed: Project Design for research on Kangaroo Impacts in Canberra Nature Park, 2015 EPD, ACT Government.

Caption: True blue Aussie, victim of petfood trade, long-standing prejudice and unproven management claims.

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