Question
With respect to the Western Hoolock Gibbons, which of the following statements is/are correct?
1
A Sanctuary in North-east India is home to this ape species listed as Endangered in the International Union for Conservation of Nature (IUCN) Red List.
2
They have specialized brachiation and can easily swing between trees.
3
They possess a strong and heavy build like gorillas, yet are remarkably agile tree climbers.
A1 only
B1 and 2 only
C2 and 3
D3 only
Each Statement — Detailed Verification
1
“A Sanctuary in North-east India is home to this ape species listed as Endangered in the IUCN Red List” — TRUE
IUCN status: The Western Hoolock Gibbon (Hoolock hoolock) is classified as Endangered on the IUCN Red List. Its population has declined by ~90% over 30 years — now fewer than 5,000 individuals remain in India.
Sanctuary in NE India · Endangered on IUCN Red List
✓ Correct
The Sanctuary: Hollongapar Gibbon Wildlife Sanctuary (formerly Hoollongapar Reserve Forest) in Jorhat district, Assam. Upgraded to Sanctuary status by the Government of Assam in 1997. It is the first Protected Area in India named after a primate species. The sanctuary houses about 125 individuals in 26 groups and is considered the largest concentration of Western Hoolock Gibbons in India.
Note on the fragmentation problem: The Hollongapar Gibbon Sanctuary is bisected by the Lumding-Dibrugarh broad gauge railway track — a serious conservation challenge.
✓ Confirmed
Hollongapar Gibbon Wildlife Sanctuary, Jorhat, Assam · India’s only gibbon-named sanctuary · IUCN: Endangered · ~125 individuals in 26 groups
2
“They have specialized brachiation and can easily swing between trees” — TRUE
What is brachiation? A mode of arboreal locomotion where an animal swings from branch to branch using only its forelimbs (arms) — without touching the ground. The word comes from Latin brachium (arm).
Specialized brachiation · Swing between trees
✓ Correct
Gibbons are the master brachiators: Their extremely long arms (longer than their legs) are precisely adapted for this. They can:
• Swing at speeds up to 55 km/hr
• Cover up to 6 metres in a single swing
• Move through the forest canopy without ever touching the ground
They are diurnal and arboreal — spending nearly all their lives in the tree canopy. Their ball-and-socket wrist joints (like a human shoulder) allow 360° rotation, enabling the continuous swinging motion.
✓ Confirmed
Long arms + ball-and-socket wrist = specialized brachiation at up to 55 km/hr · Cover up to 6 metres per swing · True master brachiators
3
“They possess a strong and heavy build like gorillas, yet are remarkably agile tree climbers” — COMPLETELY FALSE
This statement is entirely wrong — gibbons and gorillas are polar opposites in body type:
“Strong and heavy build like gorillas”
✗ Completely Wrong
Western Hoolock Gibbon:
• Weight: 6–9 kg (about the size of a house cat or small dog)
• Height: 60–90 cm
• Build: Light, slender, gracile — the opposite of heavy
• Arms: Disproportionately long (longer than legs) for brachiation
Gorilla (for comparison):
• Weight: 100–200 kg (males) — 15–30 times heavier than a gibbon
• Build: Massively muscled, heavy-boned, powerfully built
• Gorillas are ground-dwelling and knuckle-walk; gibbons never touch the ground
The irony: The very reason gibbons ARE agile tree climbers is precisely because they are light and slender — NOT heavy. A gorilla-like heavy build would make brachiation physically impossible.
✗ Factually wrong
Gibbons = 6–9 kg, slender, gracile. Gorillas = 100–200 kg, massive. Complete opposites. Agility in trees requires lightness — not gorilla-like bulk.
Gibbon vs Gorilla — Why Statement 3 Is Absurd
Western Hoolock Gibbon
Weight6–9 kg
Height60–90 cm
BuildLight & slender
LocomotionBrachiation (arms)
Ground contactRarely/never
ArmsVery long (longer than legs)
Gorilla (for comparison)
Weight100–200 kg
Height140–185 cm (standing)
BuildMassive & muscular
LocomotionKnuckle-walking
Ground contactPrimarily ground-dwelling
ArmsVery powerful, thick
Western Hoolock Gibbon — Complete Fact Sheet
| Parameter | Detail |
| Scientific name | Hoolock hoolock |
| India’s only ape | The only ape (not monkey) species found in India — tailless, no cheek pouches |
| IUCN status | Endangered (Western); Vulnerable (Eastern Hoolock = Hoolock leuconedys) |
| Range in India | All NE states south of Brahmaputra + east of Dibang river — Assam, Mizoram, Meghalaya, Arunachal Pradesh |
| Key sanctuary | Hollongapar Gibbon Wildlife Sanctuary, Jorhat district, Assam (est. 1997) — India’s only gibbon-named PA |
| Body weight | 6–9 kg · 60–90 cm tall · Light, slender build (NOT gorilla-like) |
| Locomotion | Brachiation — swings using arms at up to 55 km/hr, covering 6 metres per swing |
| Diet | Mainly fruits, insects, and leaves — frugivore |
| Social structure | Monogamous pairs — mate for life; small family groups; territorial |
| Communication | Loud calls to mark territory and locate family members; among the loudest animals relative to body size |
| Schedule I | Listed under Schedule I of India’s Wildlife (Protection) Act, 1972 — highest protection |
| Key threat | Habitat loss — population declined by ~90% over 30 years; fewer than 5,000 remaining in India |
Memory Trick — Never Forget This
🧠 Remember It This Way
Statement 3 is the easiest to eliminate: A gorilla weighs 150 kg. A gibbon weighs 7 kg. A gibbon with gorilla-like bulk cannot brachiate — it would break every branch. The very reason gibbons can swing at 55 km/hr is because they are light as a feather.
Hollongapar = India’s gibbon fortress: Hollongapar Gibbon Wildlife Sanctuary, Jorhat, Assam — remember it as the only sanctuary in India named after a primate. Named after Holong tree (Dipterocarpus macrocarpus). The railway through it is a major conservation issue.
IUCN status pair: Western Hoolock = Endangered · Eastern Hoolock = Vulnerable. Western is more threatened. Western found across NE; Eastern restricted to specific pockets of Arunachal Pradesh and Assam.
India’s only ape — not monkey: The Hoolock Gibbon is India’s only ape (no tail, more intelligent, different anatomy). All other primates in India (macaques, langurs) are monkeys. UPSC tests this distinction frequently.
