Karta had been given oral contraceptive for a number of years as she had lost all six of her babies in the past because of problems with her anatomy. However, "nature intervened", according to senior primate keeper Jodie Ellen.

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"Hopes are high that our beloved Karta will have a successful pregnancy, it's something we believe she greatly deserves," she said. "This wasn't a planned pregnancy, but nature intervened and we've proceeded with the pregnancy because Sumatran Orangutans are critically endangered in the wild and it is important we breed this species before they disappear from the planet forever."

There are fewer than 7,000 Sumatran and Bornean orangutans left in the wild and should current trends continue, they could become extinct in their native habitats in the next 10 years. Currently their population is falling by around 1,000 every year.

karta orangutan
Karta the 34-year-old orangutan is pregnant despite being on birth control Adelaide Zoo

For this reason, breeding programmes at zoos across the world are in place to protect the species.

The last time Karta was pregnant it resulted in a stillbirth. "In 2011, we discovered Karta's anatomy might be the reason she has difficulties breastfeeding. In fact, Karta's sister at Denver Zoo experiences the same problems, with keepers having to supplement feed her infant in order for it to survive," Jodie said.

Complications in pregnancy are not uncommon among apes and the zoo now plans to closely monitor Karta in the hope her pregnancy goes smoothly. "We'll be doing everything in our power to support our Karta; we have been training her for years and we have a supplementary feeding programme in place so that we can help her feed the infant when it is born," Jodie added.

"We have a group of dedicated staff that will form the primary care team and will be on site 24 hours a day once the baby arrives. We are checking remotely overnight using a new top-of-the-line camera system which will give us much greater visibility before the birth, during and afterwards.

"We now feel positive that we are on the right track and understand why Karta has had so much trouble in the past and we are hopeful that, this time around, we can help Karta have the baby she so much deserves."