After more than a year spent bringing up a baby gibbon, Auckland Zoo staff are delighted they have kept him from thinking he is a human too.
The 1-year-old siamang gibbon, named Iwani, has been successfully reunited with his family, after being hand-reared since he was seven weeks old.
Zoo staff took over the task last March after Iwani and his twin sister were rejected and injured by their mother. The female gibbon died from her injuries.
The zoo believes raising twins may have been too much for Iwani's mother Iuri, who had already nurtured five previous offspring.
Senior keeper Christine Tintinger said the decision to take over the rearing was "tough".
"Primates tend to think they're human. We knew there was the danger that if we hand-reared Iwani he could become too humanised and that his family, and other zoos, would reject him."
She said animals had been reared away from their species before, and the key to the reunion was keeping Iwani in sight and sound of his family, in a cage next door.
"As he got older we made a purpose-built cage in front of the enclosure so that his family could physically touch him and rough him up a bit to help him learn to stick up for himself," Ms Tintinger said.
"He then went into an enclosure with his brother, which was a really important step. I think he learned how to be a siamang through the physical contact with his brother."
Ms Tintinger said she had been worried the mother would bite Iwani again, or that his parents would ignore him, but this did not happen.
"Iuri isn't a touchy-feely mother, but Iwani gets the physical and social contact that he needs for his psychological wellbeing through his brother and dad."
Ms Tintinger is still bottle-feeding Iwani every morning through the bars of his enclosure, but will stop doing this at the end of the week now that he is getting accustomed to competing with others for food.
She said Iwani was slowly learning the etiquette of being a siamang.
"He's quite a stroppy little thing because he's had one-on-one attention, but he's now having to learn to accept that I'll be giving out food to others in his presence."
Ms Tintinger doesn't go into Iwani's cage any more but tries to go past every day.
"We don't want to break the bond we've established too much as its useful to have that bond so we can get close to him for such things as medical checks."
Classified as a 'near threatened' species by the World Conservation Union.
The largest of the world's nine species of gibbons.
Native to Malay Peninsula and Sumatra rainforests.
The loudest primate of all, they have a distinctive boom and bark.
Taken often for the pet trade.
Mate for life.