“Aww, she looks sad.” It’s a comment we hear all too often about our red-headed apes, the orangutans – but this is a myth that needs to be busted. 

Orangutans are one of the most closely related species to humans, sharing approximately 97 per cent of their DNA with us.

And while there are countless similarities between us, they communicate and act quite differently to us!

It's human nature to connect through facial expressions and body language – that's because we're a social bunch.

But for an orangutan, a solitary animal, the species has not evolved to use the full array of facial muscles the way a human does.

That means it's not right to assume an orangutan is unhappy or sad simply because it's sporting what looks like a sorrowful expression.

So, without human-esque facial expressions, how exactly do orangutans communicate what they're thinking or feeling?

Perth Zoo's Primate Supervisor Holly Thompson said: "Given orangutans are solitary, a lot of their communicating is done through vocalizations so that they can transmit a message across distance.

"Each vocalization means something different depending on whether the orangutan is feeling threatened, confident, or even trying to attract a mate."

Males will make a long call, that starts with soft barking before changing into long heaving roars. These long calls are used to attract female mates and also identify the caller to any surrounding orangutans.

"Orangutans are also sexually dimorphic, which means the males are a lot bigger and have the iconic round cheek flanges – these are used to amplify their call to defend their territory to any other orangutans approaching," Holly said.

Orangutans also use a kiss squeak sound to show they are agitated, a raspberry sound when building their nests, or rolling guttural sounds to warn off other orangutans threatening their territory.

It's another common misconception that ape species will smile to express joy or glee in the same way a human does.

But attributing human expressions to another species does not often work, and in this case, seeing a primate 'smile' means quite the opposite of what you might think.

"If an orangutan is appearing to grin, this is what's known as an 'appeasement grin', meaning it's not a true smile," Holly said.

"In fact, many primate species, including orangutans, will open their mouths and bare their teeth in a 'smile' as a threat or to signify they feel unsafe."

Perth Zoo is home to eight Sumatran orangutans who act as ambassadors for their critically endangered cousins in the wild.

Each has their own unique personality and uses different vocalizations or behaviors to communicate with their dedicated animal carers.

"Like humans, each orangutan is going to be different, so we're really lucky to work closely with them here at Perth Zoo and get to know each individuals' quirks and style of expression," Holly said.

"Our female Utama is also quite expressive, particularly when she's excited and playful - she'll tap her feet on the floor and open her mouth wide in delight.

It's important to remember that orangutans have one facial expression while they're at rest, and that doesn't necessarily mean they are sad, bored, or depressed – it's just their normal face!"

Since 1970, Perth Zoo has bred 29 orangutans and was one of the very first zoos in the world to create individual habitats for the individuals so they could live as they would in the wild, by themselves or mothers with their young offspring.