Those are signs a crucial matchmaking operation between two new Sumatran tigers is going to plan as the zoo plays a significant role in preserving the critically endangered animals.

The National Zoo and Aquarium has welcomed six-year-old male Aceh, from Melbourne Zoo, and eight-year-old Ndari, from Dreamworld on the Gold Coast, as part of an Australasian breeding program.

The species' population – estimated at roughly 400 animals in the wild – has been whittled down as their habitat continues to be destroyed and degraded, poachers hunt them down and traders flog animal body parts on the illegal market.

Senior wildlife keeper Renee Osterloh said the breeding pair had been assessed as a good genetic match and had been moved to the zoo where their courtship – which could take up to 18 months – had begun.

"With our breeding program what we like to see is the relationship that the two tigers have within their enclosure side by side," Ms Osterloh said. "Up and down the fence line we like to see chuffing and scent marking, smooching so to speak."

Keepers record every flirtatious detail and will monitor when the female tiger is on heat before the pair eventually meet face-to-face in the tiger's den area.

The courtship process would also include scent testing, where items from Aceh's enclosure would be introduced to Ndari as zoo staff carefully eyed her reaction.

The relationship's progression would largely hinge on her response to her prospective male mate, given female tigers could get "feisty", Ms Osterloh said.

"We want to see the reaction between the two, whether they're showing affection with things like scent marking and chuffing, we have started to see that so it's very exciting to be seeing those positive signs."

The two have been joined by four-year-old brothers Ravi and Baru, who arrived in the capital from Dreamworld in recent weeks, meaning there are now five tigers at the zoo, including female Rahni.

Ravi and Baru were trucked to Canberra from Queensland a few weeks ago and have been settling into their enclosure adjoining the zoo's Jamala Wildlife Lodge.

"They're very inquisitive, they explored the whole enclosure the first day and they like peeking up over the edge, we have the cougars and European brown bears bordering their enclosures," Ms Osterloh said. "They're both very relaxed cats."

Five tigers wa the biggest cohort the zoo has had at one time since it opened and the expanded population follows the death of the zoo's much-loved Bengal tiger, Bakkar, at age 21 in June.

The new animals were unveiled at the zoo on Thursday to mark International Tiger Day, which aims to raise awareness of tiger conservation.

Visitors to the zoo can take part in celebrations including educational tiger keeper talks, face-painting for children and feeding opportunities with the tigers on Saturday and Sunday.

Donations received across the weekend will be directed to conservation charity 21st Century Tiger.