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Gibbon Tales

What’s that noise?

On any bright morning in Tucson, the moment you step out of your car in the parking lot of the Reid Park Zoo, you might hear soft, repetitive one-note sounds, whoop, whoop, whoop, that build to a crescendo of long, sustained trills, whooOOoo, whooOOoo. You’ve just heard the morning territorial song of one of the oldest and most interesting residents at Reid Park Zoo: Billy, a 48-year-old male Lar Gibbon. 

You may recall the lineup of Primates from your school days: Lemurs, Lorises, Tarsiers, Monkeys, and Apes (which includes humans). With more than 500 species, the Primates comprise the third largest group of Mammals after Rodents (2500+) and Bats (1200+). 

The Apes are further divided into two groups, the great apes and the lesser apes, the lesser being the focus of this blog. Lesser apes include about 20 species of gibbons which live in the subtropical and tropical forests of Asia in the countries of China, India, Bangladesh, Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, and Indonesia.

The lesser apes: Small but just as mighty 

Despite the name, the lesser apes aren’t less important than the great apes; they’re just smaller in size. Fun fact: Reid Park Zoo currently cares for one of the smallest species, a Lar Gibbon, and will soon care for the largest gibbon species, a Siamang, with the new Reid Park Zoo expansion, the Pathway to Asia. 

Gibbons have different tales to tell. Unlike many of their primate cousins, they don’t make nests but prefer to sleep sitting upright, resting their heads on their knees. Gibbons are most often monogamous and, with adequate food resources, form lifelong pair-bonds. However, these animals are most known for two things: their tremendous abilities for brachiation, the way they move, and their amazing vocalization, the way they sing to maintain their territory. 

The Olympic champion of brachiators

Brachiation is the method of locomotion gibbons use to swing hand over hand in the tree canopies where they live. Among all the primates, gibbons are the true brachiator champions, traveling this way about 50% to 80% of the time. They have perfectly adapted shoulder, elbow, and wrist joints (ball and socket) which allow them to move at amazing speeds, up to 35 mph, the fastest of all non-flying mammals. Like other primates, they are also bipedal and walk upright in the trees or on the ground using their long, lanky arms to balance their gait.

Why are gibbons such Olympics-level powerhouses? They have great muscle and skeletal adaptations! They have shoulder flexors, extensors, rotator muscles, and elbow flexors with a high power or work-generating capacity, and their wrist flexors have a high force-generating capacity as well. An anatomical study done by the National Institutes of Health suggests that the elbow and wrist flexors are particularly powerful and important to their brachiating lifestyle. Despite their prowess, all individuals throughout their lives will miss a branch or misjudge a limb’s strength, and they do sustain some bone fractures from time to time, some major but most minor.

Life in the tree canopy

Gibbons are mainly frugivores and live off the fruits in the trees where they swing out their lives. They maintain individual family territories, and they know their tree-trails well. When fruit is not plentiful or not ripe enough, they supplement their diets with leaves, flowers, seeds, tree bark, and plant shoots, as well as insects, spiders, bird eggs, and, occasionally, small birds. Fruits have the highest nutritional value, leaves, flowers, and seeds less so. Seasonality and availability of ripe food sources in dry versus wet seasons and other ecological conditions, such as fragmented habitats converted to agriculture, play a large part in what individual gibbon species can consume. 

Better than any tenor at La Scala

In addition to their remarkable style of locomotion, Gibbons display some amazing vocal abilities. Despite their small size, they can produce sounds much louder than any human being can make. In the new Pathway to Asia expansion, guests will be able to meet the largest gibbon species, the Siamang, which has a specialized throat sac that it fills with air. About the size of a small balloon, this throat sac amplifies their song, so you’ll most likely hear them before you see them.

A Gibbon sings for a variety of reasons. When it sees a potential predator—perhaps a leopard or a python—it doesn’t scurry off in the opposite direction. Quite daringly, it moves closer and sings out a call as if to say, “Don’t bother, you’ve been spotted, and I can move faster.” In most cases, that’s exactly what happens because the gibbon can move faster through its well-known tree canopy-trails. 

Gibbons also sing to attract a mate or to mark an established pair-bond’s family territory. The male starts the morning song to mark the borders of its family range, and the female joins him in a duet with a different but complementary part of their song. If there are immature male or female offspring, they soon learn their mother’s song and join in for a full-throated family chorus. And they do all this while brachiating! It’s an exhilarating experience to watch this kind of morning display. 

Billy’s story

Of all the wonderful residents at Reid Park Zoo, Billy, the geriatric Lar Gibbon, is one of the most memorable. He is notable for his fluffy, some would say fuzzy, gray-black fur, white and slender hands and feet, and a white circle of fur outlining his face.

Billy was born at the Santa Ana Zoo on New Year’s Day 1973 and came to Reid Park Zoo in 1987 to become the pair-bonded mate of Moms, a female Lar Gibbon who arrived several years earlier.  The couple did their part for this endangered species.   They were companions for 30 years and had 4 offspring together, the last, a female named Lilith, born in 1999.  Moms was considered a geriatric gibbon when she died at age 47 in 2017 due to an age-related illness, so Billy became a widower at age 44. At the time of her death, they were two of the oldest Lar Gibbons in human care at any AZA institution in the U.S. 

Like all primates, Lar Gibbons are social creatures and live most of their lives as a small family unit. As gibbons have a Median Life Expectancy of about 30-40 years in human care, finding another geriatric female companion in her mid-40s, widowed, and of a compatible temperament was a monumental task. Even if one could be found, given his advanced age—Billy is old, even for his species—transporting him outside the familiar territory that he has defended daily with his morning call (34 years and counting) would be risky. With young and healthy individuals, introduction between potential mates is not without risk; with geriatric animals, it’s even more so. If she were to transfer here, she would face those same obstacles.

Due to all these factors, the AZA decided that Billy should remain at the Reid Park Zoo. He has good, trusting relationships with his Animal Care Staff who work hard to maintain his physical and mental health by making sure his days are filled with ample enrichment, such as new and differently configured ropes, hammocks, platforms, and scents, and interesting things to encounter in his habitat. 

As a fellow primate, he seems to enjoy observing humans just as much as we enjoy observing him. During the major construction project at the front of the zoo last year, Billy made a daily habit of singing his morning territorial song, then spending much of his time watching the builders excavate the dirt, install pipes, pour concrete, and plant trees. He was keen to watch it all! 

When Billy is outside sitting on one of his perches or rope swings, he watches the world go by. It’s not uncommon for Animal Care Staff to stop by for a visit accompanied by other animals on walkabout. Kenecky, a Sulphur-Crested Cockatoo, occasionally stops by for a visit, as have some of the Reid Park Zoo tamanduas. The Chilean flamingoes provided a pink-feathered parade for him when they were walked from their former habitat near the Conservation Learning Center to their new lagoon in the front plaza, and he still enjoys watching them eat from their feeding pool.

As a senior citizen, though, he is most interested in foraging enrichment where he is mentally and physically challenged (hand dexterity, nothing arduous) to look for his food inside items like puzzle feeders. Animal care staff do frequent wellness checks to make sure he is self-grooming and sleeping well, and he willingly participates in these interactions, especially if he anticipates receiving his favorite treat: a delicious ripe banana which he will carefully peel before eating.  

I encourage you to make an early morning visit to the Reid Park Zoo, and, if you’re lucky, you will hear Billy whooping while you’re still in the parking lot. Once inside the zoo, walk a few steps south of the flamingo lagoon to find him. You may be fortunate enough to see him swinging from rope to rope, platform to platform, singing his glorious morning wakeup call just to let everyone know—This is MY Lar Gibbon territory! 

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Look! Up in the sky! It’s a bird! It’s a plane! It’s a Siamang! 

Siamangs don’t fly, but sometimes they seem to. That’s because of the way they move through the treetops where they live. Siamangs (pronounced SEE-uh-mongs or SEE-uh-mahngs) brachiate to get around, and they are very good at it! They hang by their arms and swing from one branch to the next to get where they want to go. It’s like swinging on “monkey bars” on a playground. When a Siamang is moving rapidly through the treetops, it will let go of one branch and “fly” through the air like an acrobat before grasping the next branch. Siamangs can also push off with their legs and jump as far as 30 feet through the air to get from one tree to another. So, Siamangs cannot fly, strictly speaking, but if you’re lucky, you could see one seeming to fly through the air, especially in their planned habitat at the Reid Park Zoo expansion. 

Siamangs have long arms and shorter legs. Their bodies are covered by  black fur that is relatively long and shaggy. Siamangs have prominent brow ridges, and their faces have forward-facing eyes, flat noses, and relatively little fur. Adults are about two and a half to three feet long from the top of their heads to the end of their bodies, and they weigh about 25-30 pounds. Females and males are usually about the same size. They are primates, the evolutionary branch of mammals that includes humans, apes, monkeys, lemurs, and a few other species. They look a lot like monkeys, but are they monkeys? Nope – no tail.  Almost all monkeys have tails, and apes do not; Siamangs don’t have tails. More specifically, these acrobatic apes are a type of gibbon, in fact, the largest type of gibbon. 

Siamangs have some physical features that are very useful for brachiating, or swinging around with their l arms above their heads. Like other gibbons, Siamangs’ arms are very strong and extremely long – a Siamang’s arm span is usually about two and a half times the length of its body! (If your arms were that long compared with your body, they would stretch 10 to 15 feet from fingertip to fingertip!) Anyway,  Siamangs’ thumbs are unusual, too. They are much shorter than the Siamang’s fingers and they are located higher on the wrist than other primates’ thumbs. Because of this, a Siamang’s hand looks more like a hook than other primates’ hands. And Siamangs have very flexible shoulder joints. The combination of long, strong arms, hook-shaped hands, and very flexible shoulder joints allows a siamang to swing rapidly from handhold to handhold and tree to tree. An adult Siamang can move through the treetops at 35 miles per hour – about as fast as a tiger can sprint!

The amazing Siamangs heading our way are one big reason we are looking forward to the Reid Park Zoo expansion. But be prepared to look UP – they will have elaborate climbing and swinging equipment in their roomy habitat. But they have to come down to ground sometimes, don’t they?

On the occasions when Siamangs come down to the ground, they normally walk on just their hind legs, holding their extremely long arms in the air for balance and to keep them from dragging on the ground. But Siamangs are much slower and more vulnerable to predators on the ground, so they spend most of their time high in the treetops, where they can avoid and elude predators very well. 

Question: What does a Siamang have in common with a green tree frog? Siamangs have another unusual physical feature that is unique among species of gibbons: inflatable throat sacs. Both female and male Siamangs have a sac of skin on the front of their throat that sits flat and barely visible at rest, but that the animal can inflate with air until the sac is the size of the animal’s head! The inflated throat sac gives extra resonance and volume to the Siamang’s  unmistakable call, a combination of hooting similar to other gibbons and a rapid “barking” that sounds a bit like a dog. Siamangs use their calls to gather together members of their clan and to warn members of other clans not to intrude on their territory. 

Siamangs live in family groups and generally mate for life– a given male and female Siamang normally stay together for years. Their offspring stay with them for 5-7 years, until they reach maturity. A Siamang infant clings to its mother and is mainly cared for by its mother for the first 8 months, but is cared for mainly by its father in its second year of life. Wildlife biologists estimate that Siamangs live for somewhere between 25 and 40 years in the wild, and longer than that in zoos, up to 44 years. Reid Park Zoo’s male Lar Gibbon – a species closely related to Siamangs – currently is 49 years old! 

Siamangs are diurnal animals – awake during the day and asleep at night. They usually wake after sunrise, spend up to an hour emitting their characteristic call to announce their territory, and then spend several hours foraging for food. Siamangs eat mainly fruit and tender leaves of bamboo and other plants, along with some insects, eggs, and occasional small vertebrates. Foraging for food requires several hours of a Siamang’s day. By eating fruit and later defecating out the seeds, they’re helping to shape their environment by spreading seeds around their habitat.  In the afternoons, they usually rest, groom themselves and each other, and travel to that night’s sleeping area. Instead of lying down on a bed of leaves or branches, they sleep sitting upright in trees. 

The amazing Siamangs are one more reason we are looking forward to the Reid Park Zoo’s Pathway to Asia expansion!

Siamangs live in tropical forests in Asia. In the past, their range was wider, but now they are found only in the mountains of Malaysia and the nearby Indonesian island of Sumatra. Adult Siamangs really have no natural predators, but even so they are classified as Endangered by the International Union for Conservation of Nature because their number in the wild has been estimated to drop by half in less than 50 years. Threats to Siamangs in the wild come from humans, mainly from an illegal pet trade and destruction of their habitat. Clear-cutting and burning forest land, the Siamang’s natural habitat, in order to grow palm trees for palm oil is an especially common problem. You can help to protect these amazing animals by speaking out against illegal wildlife trading and by choosing products that use sustainable sources of palm oil. Oh, and you’ll be helping their conservation every time you visit them at the Reid Park Zoo. Spread the word!