Call them the odd couples.
The friendship between 5-month-old female baby primates Nia and Irma and cubs Dema and Manis has blossomed at the Taman Safari zoo, where they share a room in the nursery.
After being abandoned by their mothers shortly after birth, the four play fight, nipping and teasing each other, and cuddle up for a shared nap when they are worn out.
"This is unusual and would never happen in the wild," zoo keeper Sri Suwarni said Wednesday. "Like human babies, they only want to play."
The four have lived side-by-side for a month without a single act of hostility, she said.
The exceptional friendship will likely be short lived, because as the animals grow up their natural survival instincts will kick in, veterinarian Retno Sudarwati said.
"When the time comes, they will have to be separated," she said. "It's sad, but we can't change their natural behavior. Tigers start eating meat when they are three months old."
Sumatran tigers and orangutans are endangered species, threatened by rapidly shrinking habitats, reports AP.
Conservationists estimate there are fewer than 700 Sumatran tigers still alive, while fewer than 60,000 orangutans remain in the wild.
Around 90 percent of their jungle habitat has been destroyed by illegal logging, poaching and cut-and-burn farming practices on Borneo and Sumatra islands, conservationists estimate.