The rare striped legless lizard and earless dragon, native to Canberra and in serious decline in recent years due to drought and over-grazing, are now at stable numbers, and grasses are returning to their normal, varied levels, says ecologist Melissa Snape.

Dr Snape, a senior researcher in the ACT government’s Environment, Planning and Sustainable Development Directorate, says in the lead-up to each yearly cull, she and her team spend many hours counting local kangaroo populations, and deciding how to keep them to sustainable levels.

“We've got a really good understanding of what grass structure is best for biodiversity, and we've also looked at what levels of kangaroo grazing create that sort of grass structure,” she said.

“From monitoring the results of the conservation culling, we've been able to show that the culling has been effective in terms of reducing kangaroo density to the levels that we expect. In some reserves, we've reduced kangaroo numbers to levels that we're happy are sustainable in terms of maintaining grass structure, so we don't have to cull those reserves every year anymore.”

This meant that the cull could then move to other over-populated reserves, which explained the fluctuating numbers of kangaroos being culled each year.

This year, the program has a culling target of up to 3253 kangaroos, 1000 more than last year, while shooters move into new areas such as West Majura and Aranda.

In the meantime, Dr Snape said, less grazing meant a better “variable grassy layer”, able to provide the right habitat for various small native species, as well as enough food for the remaining kangaroo population to thrive.

But many animal liberationists maintain that the science being carried out by Dr Snape and her fellow ecologists is faulty, and that Canberrans have been misled for the past 10 years about the over-abundance of kangaroos in the first place.

Frankie Seymour, from the Animal Protectors Alliance, said the cull had nothing to do with environmental considerations.

“As far as we're concerned, as far as pretty much every independent scientist in Australia is concerned, there is no ecological basis for the cull,” she said.

“We believe that it is entirely motivated by support for development and support for farmers.”

She said evidence from ACT government or even Australian National University scientists supporting the culls could not be trusted, and was not adequately peer reviewed.

“[The culling program] is extremely cruel and it's also ecologically catastrophic because they are actually going to get rid of all these kangaroos,” she said.

She said the argument that rising kangaroo populations were due to a lack of any natural predators was “absolute nonsense”.

“We have foxes in the ACT and the foxes take up to 90 per cent, sometimes even 100 per cent of young joeys, so they've got just as many predators as they've ever had,” she said.

Dr Snape agreed that while foxes were potential predators of joeys in urban reserves - along with domestic dogs, eagles and cars - the numbers actually being killed varied depending on the site and the year.

“By counting reserves every year, we are able to carefully document population growth rates – even accounting for any culling – so we are quite confident in these figures and our capacity to predict site-specific growth rates,” she said.

ACT Parks and Conservation Service director Daniel Iglesias agreed that the scientific findings about the consequences of persistent over-grazing were clear, and many of the studies were published on the government's website.

“Some people just do not agree with killing animals for any reason, and I'm not going to judge that, but my perspective is not that one,” he said.

“My perspective is environmental health, and if the evidence says that for the benefit of the environment this needs to happen, then I've got to propose to do it.”