Breeding animals in the zoo is not as simple as putting any male and female together and expecting them to mate.
Zoologists around the world work behind the scenes to find the perfect match for animals in order to ensure good genetic diversity.
They do this with the help of studbooks, which are online databases on the parenting history of animals.
A demographic and genetic analysis is then done based on the data so that breeding programme coordinators can find out which two animals should be bred together.
Dr Cheng Wen-Haur, chief life sciences officer and deputy chief executive officer of Wildlife Reserves Singapore (WRS) - which manages the Singapore Zoo - said the ultimate goal for breeding animals under human care is to ensure that their populations can be self-sustaining.
"You breed them cooperatively for all the institutions that hold them around the world so you don't have to keep taking them from the wild," said Dr Cheng.
One example would be the two Goodfellow's tree kangaroos which arrived at the Singapore Zoo from Australia in June and July this year. The two kangaroos are classified as endangered under the International Union for the Conservation of Nature Red List of Threatened Species due to unsustainable hunting and loss of habitat.
It is hoped that both will start their own family here, as an "assurance colony" in Singapore, under a global plan to ensure the species' survival.
WRS also wants to breed other species like the red panda and emperor tamarin, a kind of small monkey known for its long white moustache.
More than 700 baby animals were born or hatched in WRS parks last year.
Globally, San Diego Zoo in the United States is among the zoos that stand out for their success in breeding animals. It has won numerous awards for breeding several animals successfully, including koalas and thick-billed parrots. It received an award in 1961 for the first koala birth in the Western Hemisphere, said the zoo's website.
Wildlife consultant Subaraj Rajathurai said studbooks help to ensure that the gene pool of a particular species does not become too small.
"If the zoo has only a small number of each species, and you try to breed them with the small numbers you have, the offspring will become non-viable due to inbreeding," he said.
Dr Cheng said the ultimate aim of breeding animals under human care is to release them into the wild.
But this is often hard to do with the increasing destruction of animal habitats. "Most of the time, the wild is not ready to take them back," he said.