A contraceptive program to manage kangaroo populations will be expanded to more locations in Canberra, following the successful start to the program at Mulligans Flat.
But the program will never be able to completely replace kangaroo culls, which are needed to manage large and mobile kangaroo populations.
Government ecologists administered the GonaCon contraceptive vaccine to 41 female Eastern Grey Kangaroos at Mulligans Flat in Canberra's north earlier this year.
GonaCon was developed in the United States, where it is used in white-tailed deer, wild horses and burros. Australia's Commonwealth Scientific and Industrial Research Organisation has been assessing its effects locally over a long period.
Claire Wimpenny, a senior ecologist at the ACT government's Environment, Planning and Sustainable Development Directorate, said work was underway to administer the vaccine solely by dart.
Kangaroos have been sedated with a dart in the most recent roll out before ecologists inject the contraceptive by hand.
"We've been doing some trials with a dart that injects GonaCon and also sprays a paint on the animal's fur ... That's just a temporary mark that helps us identify which individuals we've done in a particular treatment period; paint does wash off. What we'd do in future years is assess how many females have pouch young," Ms Wimpenny said.
Ms Wimpenny said the purpose of contraceptive treatments was to maintain a stable population and modelling had shown about 70 per cent of a kangaroo population's breeding-age females needed to be treated.
"The beauty of the way we've decided to use GonaCon is that we're just treating adult breeding females - that means young females get to grow up and have a young before they're treated, at least one - so we've got a low level of breeding happening," she said.
"Then each year you can assess and you can say, 'Hmmm, actually, given the conditions and given what we're seeing in terms of breeding, we don't want to treat as many this year'."
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Culls will still be required to manage kangaroo populations in parts of the ACT, Ms Wimpenny said.
"There are some sites where we cull kangaroos where this sort of technique ... isn't going to be appropriate," she said.
"We don't see [contraceptive treatments] as something that's going to replace culling everywhere. We see that it's a really potentially useful tool in some of the smaller, more contained nature reserves that we've got and the intention is that the use of the GonaCon will reduce the need for culling in future at those sites."
The ACT government will spend $1.2 million on fertility control treatments as part of its annual kangaroo management program through to June 2025.
Preliminary results on the effectiveness of contraceptive vaccine treatments administered to kangaroos this year will become available in 2024.
Environment Minister Rebecca Vassarotti in April said the ACT wanted to make sure its kangaroo management practices were the most humane in the country.
"We know we need to address over population in ecologically sensitive areas and we have been working for decades to trial non-lethal methods," Ms Vassarotti said.
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