Inquisitive eight-month-old Tucker was recently joined by a second joey, who rangers estimate to be about four months old.

While visitors to the koala enclosure can expect to see Tucker out, about and exploring, the newest arrival, another boy, is still enjoying the warmth of mum's pouch.

Tucker was born to mum Yellow, and the yet-to-be-named youngster to mum Scully. Dad Jed is the only breeding male at the reserve.

Tidbinbilla Nature Reserve wildlife officer Meaghan O'Connor described Tucker with affection.

"I think he's very calm, he is confident in himself coming down the tree without mum, and he's a little bit adventurous as well. He does like to get on to the other koalas' backs and have a look around," she said.

"I think he's a bit of a joy for Tidbinbilla."

Koalas have a long history in the ACT, but are listed as a threatened species.

According to ACT Parks and Conservation Service regional manager Brett McNamara, while not common, they were known to be in the region prior to European colonisation.

Tidbinbilla celebrated 80 years this year, and introduced koalas in 1939, just three years after its inception.

The population thrived up until the 2003 bushfires, when the area was burnt to the ground.

"To walk into the enclosure back in 2003, it was completely decimated," Mr McNamara said. "It was like a bomb had gone off in here, it was quite horrific. Even for me just to stand here today looking around, to remember what it was like then compared to what it is like now, we've come a long, long way and that's what nature can do, it's wonderful."

Lucky was the only koala to survive the bushfires, and he remained the sole koala at the reserve until 2007 when he died from old age.

For six years, there were no koalas at Tidbinbilla. In 2013, seven females all with back young were relocated from the Otways to the ACT.

The baby koalas have come as a result of the Otway back young reaching breeding age.

"It's a rather unique experience to have koalas back here at Tidbinbilla," Mr McNamara said.

Ms O'Connor said it was a fantastic opportunity for the Canberra community.

"It is absolutely amazing," she said.

"It is such a big visitor experience for people to be able to come out, and especially in the free range enclosure because they actively have to look for koalas themselves, so that in itself is an experience, but everybody loves young of anything so it's a big ticket just having the joeys there."

Help name the new koala joey, as part of a competition to win a personal ranger-guided tour to learn more about koalas at Tidbinbilla.

The name must be creative, preferably Indigenous, and relating to Tidbinbilla or nature.

Send in your suggestion with the subject 'Koala name' to tidbinbilla@act.gov.au along with your own name and contact details.