Curious Canberra answers questions sent in by you, the audience. This one is from Robyne Zibar, who saw something strange while walking in Weston Park.

Loading...

When you're a nature lover, you notice the little things that come with being outdoors.

For Robyne Zibar, a retiree from Fisher, going for a walk with her husband Ralf is a meditative experience.

"We take it all in," she said. "We listen to the birds and enjoy the smells, the quietness."

The couple have been walking in Weston Park for over 20 years, so it's no surprise that Robyne noticed a change in the kangaroo population late last year.

"I noticed that I couldn't see any kangaroos, and I wondered where they went because we could usually find their hiding places," she said.

"The next time we came, we discovered that there are these kangaroos with huge collars and tags, they're blue and white, so they stick out like a sore thumb."

Robyne feared that the kangaroos were going to be moved to make way for development.

She sent her question to Curious Canberra, and soon I was at Weston Park introducing her to Claire Wimpenny, a senior ecologist from the ACT Government.

A test site for a fertility drug

"The kangaroos here at Weston Park are part of a fertility trial program," Claire explained.

"We're trialling a fertility control vaccine called GonaCon and the hope is that that could provide an option for managing kangaroo populations in the ACT."

ACT Government senior ecologist Claire Wimpenny. ( ABC News: Sonya Gee )

The trial was announced in 2015 and is now underway at five different sites.

The vaccine was given to 35 female kangaroos at Weston Park, and if the trial is successful, kangaroos at this site won't reproduce for at least three years.

"The fact that it's not permanent gives you a lot of flexibility about how you mange," Claire said.

"You can assess the population one year and say, 'Yes we think we should vaccinate some of the females,' or you can decide, 'No, we're happy for them to breed again.'"

As part of the trial, vaccinated kangaroos were given collars and ear tags, to help researchers identify and track them over the next few years, to see if the drug has worked.

Capturing kangaroos, one at a time

ACT Government ecologists weigh a kangaroo at the Australian National Botanic Gardens. ( Supplied: ACT Government )

There are around 80 kangaroos at Weston Park, and it was chosen as a test site because the population is manageable and approachable.

This was crucial given the way female kangaroos are captured, vaccinated and tagged.

"It is quite a complicated method to catch a kangaroo and collar it," Claire said.

"We do this by darting the kangaroo."

A gas-powered gun is used to fire a dart containing an anaesthetic into the rump of the kangaroo. The animal is asleep within three to five minutes, which enables ecologists to move it to a processing area and perform a number of tasks, including administering the vaccine by hand.

"Then we fit them with a very light vinyl collar which helps with long distance identification."

It's a labour intensive process and Claire estimates that a maximum of 11 kangaroos were vaccinated at Weston Park in a single day, which involved a team of five or six people.

Community concern

Curious Canberran Robyne Zibar watching kangaroos at Weston Park. ( ABC News: Sonya Gee )

It's not the first time the drug has been used in the ACT as part of this trial, however Claire believes Weston Park is one of the most obvious research sites to date.

"The kangaroos here at Weston Park are pretty famous with visitors and locals, so while we were doing our work there were lots of people that were coming past," she said.

She recalled one young man who spotted a kangaroo that was recovering from anaesthetic who made a phone call to find help. Claire was keeping an eye on the kangaroos at the time, and was able to explain what was happening.

After hearing about the trial, our question-asker Robyne asked whether the vaccine affects the social dynamics of the group.

"As far as we know, there's no implications of [the fertility control agent] affecting behaviour in the group but that's something that will need to be looked at," Claire said.

The kangaroo collars are made of vinyl and are fitted to allow for growth. ( ABC News: Sonya Gee )

Robyne also had concerns about the size of the collars. Claire brought a sample kangaroo collar for Robyne to handle.

"From afar, it looks like it's really solid and heavy but it's quite light and pliable," Robyne said.

According to Claire, the collars are made of a lightweight vinyl, and fitted to allow for growth.

"Kangaroos have remarkably small necks, they have lots of fur around their necks," Claire said.

"We haven't had any issues with these."

Keeping watch

Ecologist Claire Wimpenny and Curious Canberran Robyne Zibar look for collared kangaroos at Weston Park. ( ABC News: Sonya Gee )

Once a month Claire visits Weston Park to check on the kangaroos that are part of the trial.

Armed with binoculars, she tries to check off the 35 vaccinated kangaroos, using their collars and ear tags to identify them.

Right now, it's too early to tell whether the drug has worked.

"Most kangaroo births happen in the summer time, so we're just getting to the end of that breeding period now," Claire said.

While she expects the GonaCon vaccine is working in these kangaroos, she'll have to wait until September for firm results.

"Because the kangaroo young are born so tiny, it's not until they're quite advanced and get close to the age when they're getting out of the pouch that we can say whether or not there's young there," she said.

Could the vaccine replace culling?

Collared kangaroos at Weston Park are part of a fertility control trial. ( ABC News: Sonya Gee )

The vaccine is a non-lethal way of staying on top of the kangaroo population but it's unlikely to replace culling completely.

In this trial, all of the kangaroos have been captured and vaccinated by hand.

Claire estimates that this costs around $1,000 per kangaroo, which covers the intensive monitoring that's part of this project, costs that wouldn't apply if the drug was used outside of a research setting.

Work is now being done on dart-delivery, where the vaccine would be darted straight into the kangaroo, and then retrieved by ecologists.

It's thought that this method would speed up the process and be significantly cheaper.

"If that works, that could provide a more usable method for controlling the kangaroos," Claire said.

"At this stage, we're not envisaging that this fertility control could replace culling completely, but it might replace it in some areas and it might mean less culling in some areas."

Want to have your question answered? Curious Canberra is always open.