Labor MLA Michael Pettersson, who supports the cull program, presented a petition to the ACT Assembly last week organised by John Grace and Jane Robinson, retired senior public servants who have committed hundreds of hours walking Canberra's nature parks counting kangaroos.

They have compiled a 50-page report detailing their observations of kangaroo numbers in 37 Canberra nature parks over 12 months, complete with testimonials.

The Evatt couple have called for an independent review of the Environment Directorate's kangaroo management plan, claiming eastern grey numbers were grossly overstated.

The annual cull, under way now until July 31, aims to see 1650 kangaroos removed from nine reserves. Adults will primarily be shot. Joeys will be killed using nationally approved methods, which includes a single forceful blow to the skull, or stunning.

The cull has been deemed a necessary evil by those involved, a way of protecting both native grasslands and the roos themselves, with burgeoning numbers leaving them vulnerable to starvation when the rain disappears.

Ms Robinson said their concern began after the 2019-2020 bushfires, when billions of native animals were estimated to have died across Australia.

"We were really concerned that on top of that horrific event, the ACT government was then calling for kangaroo culling in the Canberra nature parks yet again," she said.

Ms Robinson said she and Mr Grace spent approximately two hours each walking through 37 of the ACT's 39 nature parks. The pair said they recorded every kangaroo in a systematic, methodical way, in each of Canberra's parks accessible by foot.

Based on that work, they believed there were about 4074 kangaroos in all Canberra's nature reserves combined.

The ACT Environment Directorate estimated 16,823 kangaroos across 15 reserves, with one kangaroo per hectare their preferred volume to preserve ecosystems.

There was no official calculation for how many kangaroos there were in the ACT and not all reserves were counted, as not all parks contained endangered grasses.

Rangers conducted walk-throughs of reserves where endangered grasses exist, with an understanding higher densities of kangaroos existed in grassland areas, compared to other forests where there was comparatively little grass to eat.

Ms Robinson said kangaroos had been made a "scapegoat" for the demise of endangered species in the ACT, including the pink-tailed worm lizard, the striped legless lizard and the golden sun moth, despite kangaroos not being listed as key threats.

"The threats to these critters are listed as a loss of habitat, urbanisation, industrialisation, infrastructure development, agricultural practices, use of weed asides, herbicides, feral animals, such as cats and foxes," she said.

"It's a giant con to claim that kangaroos should be killed."

The ACT's conservator of flora and fauna Ian Walker said the annual cull number was decided each year on two things: an estimated number of kangaroos and the height of grass in the reserves.

To count the roos, park rangers walked a line through multiple sites on multiple reserves. The number observed during the site walk was extrapolated to the rest of the park.

"That methodology has been peer-reviewed and is a standard methodology for counting animals, in particular kangaroos," Mr Walker said.

He said the kangaroos fed off the grass which provided habitat to endangered species, with temperate grassland also at risk when numbers were too high.

In years when rain was plentiful fewer kangaroos were removed from the park, he said.

In drought years the annual cull would be higher to allow the grasslands to recoup.

Parks officers reported the cull as being the worst part of their job. This year they introduced dart-delivered contraceptives in the hope of reducing the annual cull number.

Red Hill will be included in the cull program for the first time this year, after the directorate observed an increase in eastern grey populations.

Mr Walker said ecologists were looking at trends over a lengthy period of time and the count did not take in the entire ACT. He said putting an exact number on kangaroos in the territory each year was not possible, nor was it really the point of the management program.

"It's a bit like asking, 'How many birds are in the ACT'?" he said.

"What we've done is calculated and counted numbers in particular reserves and we know we've got very good kangaroo number estimates over the last decade."

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George Wilson, an Australian National University Honorary Professor, has researched kangaroo management for more than 40 years.

Prof Wilson said the problem with kangaroo management in Australia was the lack of a national strategy.

"The only jurisdiction in Australia that actually is clearly answering what it's trying to achieve with kangaroos is the ACT. They're way out in front of all the other jurisdictions," he said.

Prof Wilson said there was between 40 to 50 million kangaroos in Australia, with most of them on pasture properties or grazing properties.

"There is absolutely no chance that killing or commercial use of kangaroos is going to have any effect upon the survival of the red and grey kangaroo," Prof Wilson said.

"Doing nothing is not a management objective, it's an abrogation of responsibility for all the other biodiversity and the kangaroos themselves."

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