Helarctos malayanus (Raffles, 1822)

Etymology

The sun bear (Helarctos malayanus (Raffles, 1822)) gets its common name from its distinctive orange to cream-coloured, crescent-shaped chest patch.

General Morphology

It is the smallest species of bear, with a stocky build, large paws, strongly curved claws, small rounded ears, and a short snout.

Body Size

Its head-and-body length ranges from 100 to 140 cm (39 to 55 in), and shoulder height reaches nearly 70 cm (28 in).

Sexual Dimorphism and Weight

Adult males are roughly 10 to 20% larger than females, and adults weigh between 25 and 65 kg (55 to 143 lb).

General Coloration

The snout can be grey, silver, or orange; fur is typically jet black, but may range from grey to red.

Fur Characteristics

Its fur is silky, fine, and the shortest of any bear species, an adaptation to its hot tropical habitat.

Chest Patch Appearance

The characteristic chest patch is most often U-shaped, but may also be circular or spot-like, and ranges in colour from orange or ochre-yellow to buff, cream, or even pure white.

Chest Patch Variation

Some individual sun bears do not have this patch at all.

Threat Display Behavior

When threatened, sun bears can stand on their hind legs to display the chest patch as an intimidation display toward enemies.

Juvenile Coloration

Infant sun bears are greyish black with a pale brown or white snout, and their chest patch is dirty white; older juveniles may have dark brown coats.

Adult Fur Structure

In adults, the underfur is particularly thick and black, while the longer guard hairs are lighter.

Shoulder Hair Patterns

Two hair whorls sit on the shoulders, from which hair radiates outward in all directions.

Neck and Chest Hair Patterns

There is a crest along the sides of the neck, and an additional whorl in the centre of the breast patch.

Paw Adaptations

The edges of the paws are tan or brown, and the soles have no fur, which is likely an adaptation for climbing trees.

Claw Morphology

Claws are sickle-shaped, and the front claws are long and heavy.

Tail Length

The tail is 3 to 7 cm (1.2 to 2.8 in) long.

Sympatric Similar Species

The sympatric Asian black bear has similarly shaped cream-coloured chest markings, but differs in its claw markings.

Feeding Adaptations

When feeding, the sun bear can extend its exceptionally long tongue to collect insects and honey.

Dentition and Bite Force

Its teeth, particularly the canines, are very large, and its bite force quotient is high relative to its body size, for reasons that are not well understood.

Bite Force Functional Hypothesis

One possible explanation is that this trait helps it frequently open tropical hardwood trees with its powerful jaws and claws to access insects, larvae, or honey.

Bite Force Measurement

For its body size, its bite force is very strong: a 50 kg (110 lb) sun bear produces a maximum bite force of 1907.3 to 2020.6 Newtons on the rear molar.

Head Morphology

The head is large, broad, and heavy in proportion to the body, while the ears are proportionately smaller, and the palate is wide in relation to the skull.

Climbing Adaptations

A number of unique anatomical traits, including inward-turned front feet, a flattened chest, and powerful forelimbs with large claws, all indicate adaptations for extensive climbing.

Subspecies Taxonomic Status

Currently, the status of sun bear subspecies is unsettled.

Synonym History

H. annamiticus, described from Annam in 1901, is not recognised as a distinct species and is treated as a junior synonym of H. m. malayanus.

Proposed Subspecies Rejection

In 1906, Richard Lydekker named the subspecies H. m. wardii for a sun bear skull, noting similarities to a purported Tibetan specimen with a thicker coat, but this Tibetan specimen was later confirmed to be an Asian black bear (Ursus thibetanus).

Monotypy Argument

Genetic differences between the two proposed subspecies are unclear, so some researchers consider the entire species monotypic.

Native Range

The sun bear is native to the tropical forests of Southeast Asia.

Range Boundaries

Its range is bounded by northeastern India to the north, and extends south through Bangladesh, Myanmar, Thailand, Cambodia, Laos, and Vietnam, all the way to Brunei, Indonesia, and Malaysia.

China Distribution Record

Its presence in China was only confirmed in 2017, when individuals were sighted in Yingjiang County, Yunnan Province.

Local Extirpation

The species is currently extinct in Singapore.

General Habitat Types

Throughout its range, sun bears primarily inhabit two main forest types: deciduous and seasonally evergreen forests north of the Isthmus of Kra, and non-seasonal evergreen forests in Indonesia and Malaysia.

Altitude Preference

They are typically found at low altitudes, for example below 1,200 m (3,900 ft) in western Thailand and Peninsular Malaysia, but elevation preferences vary across their range.

Indian Altitude Records

In India, larger populations have been recorded at elevations up to 3,000 m (9,800 ft) than in low-lying areas, most likely due to lowland habitat loss.

Northern Range Limitation

They occur in montane areas of northeast India, but do not extend farther north into the colder, unfavourable Himalayan region; their distribution is restricted to the northwest in part due to competition with sloth bears.

Mainland Sympatry

Across the remaining mainland range, which includes mixed seasonal forest types with monthly rainfall below 100 mm (3.9 in) for 3 to 7 months each year, the sun bear is sympatric with the Asian black bear.

Elevational Niche Partitioning

In mountainous areas, Asian black bears are more common than sun bears, probably because of a scarcity of the invertebrates that sun bears feed on.

Southern Habitat Types

In southern Thailand and Peninsular Malaysia, the main habitats are moist evergreen forests with a relatively stable climate and heavy rainfall year-round, alongside low-lying or montane dipterocarp forests.

Mangrove Habitat Use

Sun bears may inhabit mangroves, but only when mangroves are located close to their preferred habitat types.

Anthropogenic Habitat Use

Sun bears generally avoid heavily logged forests and areas close to human settlement, though they have been observed in farmlands, plantations, and orchards, where they are sometimes considered pests.

Plantation Crop Damage

A survey in Lower Kinabatangan Segama Wetlands found that while sun bears were feared in oil palm plantations, they were not common there; Bornean bearded pigs, elephants, and macaques cause far more crop damage.

Livestock Predation

Sun bears have been reported preying on poultry and livestock.

Pleistocene Fossil Range

Fossil evidence shows that sun bears occurred farther north during the Pleistocene, and may have ranged as far south as Java during the middle to Late Pleistocene.

Pleistocene Fossil Fauna

Middle Pleistocene sun bear fossils have been found in Thailand alongside Stegodon, gaur, wild water buffalo, and other living and extinct mammals.

Contemporary Population Trend

Today, the sun bear is locally extinct across most of its former range, especially in Thailand, and populations are declining in nearly all range countries.

Singapore Extinction Cause

It disappeared from Singapore between the 1800s and 1900s, likely due to extensive deforestation.

Range Population Gradient

Sun bear population sizes tend to decrease moving northward from Sundaland, and numbers are particularly low at the northern and western edges of the current range.

Gradient Origin

This pattern may have existed since prehistoric times, and is not solely a result of human activity.

Population Density

Population density varies across the species' range, from 4.3 to 5.9 individuals per km² (11 to 15 individuals per sq mi) in Khao Yai National Park to 26 individuals per km² (67 individuals per sq mi) in the Harapan Rainforest in southern Sumatra.

Arboreal Lifestyle

Of all bear species, the sun bear has the most arboreal lifestyle.

Climbing and Resting Habits

It is an excellent climber, and often sunbathes or sleeps in trees 2 to 7 m (6 ft 7 in to 23 ft 0 in) above the ground.

Resting Site Types

Its resting sites are most commonly fallen hollow logs, but it also rests in cavities of standing trees, in cavities under fallen logs or tree roots, and on high tree branches.

Swimming Ability

It is also an efficient swimmer.

Social Structure

Sun bears are generally solitary, though pairs (most often mothers and cubs) are sometimes seen together.

Sensory and Threat Behavior

Sun bears stand on their hind legs to get a wider view of their surroundings or detect distant scents; when threatened, they attempt to intimidate enemies by displaying their chest patch.

Vocalisations

Vocalisations produced by sun bears include grunts and snuffles while foraging for insects, and roars similar to those of male orangutans during the breeding season.

Alarm Vocalisation

Less commonly, sun bears give short barks when surprised.

Hibernation Absence

Sun bears do not hibernate, most likely because food resources are available year-round across their range.

Activity Pattern

They are primarily active during the day, though they are more often nocturnal in areas frequently visited by humans.

Cognitive Ability

Sun bears are noted for their intelligence: one captive individual observed sugar being stored in a cupboard locked with a key, and later used its claw to open the lock.

Facial Mimicry Ability

A 2019 study documented that sun bears can skillfully mimic the facial expressions of other sun bears, with a level of precision comparable to that seen in gorillas and humans.

Home Range Size

Sun bear home ranges vary in size across different areas.

Specific Home Range Measurements

In Borneo and Peninsular Malaysia, they range from 7 to 27 km² (2.7 to 10.4 sq mi), while in Ulu Segama Forest Reserve in Sabah they range from 8.7 to 20.9 km² (3.4 to 8.1 sq mi).

Predators

Tigers are the main predator of sun bears; dholes and leopards have also been recorded preying on sun bears, but such cases are relatively rare.

Predator Interaction Record

In one recorded incident, a prolonged fight between a tiger and a sun bear resulted in the death of both animals.

Python Predation Record

In another incident, a large reticulated python in East Kalimantan swallowed a wild female sun bear.

Human Interaction

Sun bears usually do not attack humans unless they are provoked, injured, or guarding cubs; their timid nature meant they were often tamed and kept as pets in the past, though they can act fiercely if surprised in the forest.

Reproductive Cycle

Sun bears are polyoestrous, and births can occur throughout the year.

Oestrus Duration

Oestrus lasts five to seven days.

Sexual Maturity Age

Sun bears reach sexual maturity between two and four years of age.

Gestation Period

Reported gestation lengths range from 95 to 240 days; pregnancies tend to be longer for zoo-kept sun bears in temperate climates, possibly due to delayed implantation or fertilisation.

Birthing Site

Births take place inside hollow tree cavities.

Litter Characteristics

A litter typically has one or two cubs, each weighing around 325 g (11.5 oz).

Neonatal Traits

Cubs are born deaf, with their eyes closed.

Cub Development Milestones

Their eyes open at around 25 days old, but they remain blind until 50 days after birth, and their sense of hearing improves over the first 50 days.

Cub Physiological Dependency

Cubs younger than two months old rely on external stimulation to defecate.

Cub Rearing Site

Cubs are kept on buttress roots at the base of trees until they learn to walk and climb properly.

Maternal Care

Mothers protect their cubs aggressively.

Offspring Dependency Period

Offspring stay with their mother for roughly the first three years of their lives.

Lifespan

In captivity, sun bears generally live for more than 20 years; one individual lived to 34 years of age.