The sun bear (Helarctos malayanus) is a species in the family Ursidae (the only species in the genus Helarctos) occurring in the tropical forests of Southeast Asia. It is the smallest bear species, standing nearly at the shoulder and weighing . It is stockily built, with large paws, strongly curved claws, small, rounded ears and a short snout. The fur is generally short and jet black, but can vary from grey to red. The sun bear gets its name from its characteristic orange to cream-coloured chest patch. Its unique morphology—inward-turned front feet, flattened chest, powerful forelimbs with large claws—suggests adaptations for climbing.
The most arboreal (tree-living) of all bears, the sun bear is an excellent climber and sunbathes or sleeps in trees above the ground. It is mainly active during the day, though nocturnality might be more common in areas frequented by humans. Sun bears tend to remain solitary, but sometimes occur in twos (such as a mother and her cub). They do not seem to hibernate, possibly because food resources are available the whole year throughout the range. Being omnivores, sun bears' diet includes ants, bees, beetles, honey, termites, and plant material such as seeds and several kinds of fruits; vertebrates such as birds and deer are also eaten occasionally. They breed throughout the year; individuals become sexually mature at two to four years of age. Litters comprise one or two cubs that remain with their mother for around three years.
The range of the sun bear is bounded by northeastern India to the north then south to southeast through Bangladesh, Cambodia, Myanmar, Laos, Thailand, and Vietnam in mainland Asia to Brunei, Indonesia, and Malaysia to the south. These bears are threatened by heavy deforestation and illegal hunting for food and the wildlife trade; they are also harmed in conflicts with humans when they enter farmlands, plantations, and orchards. The global population is estimated to have declined by 35% since the 1990s. The IUCN has listed this species as vulnerable.
Etymology
The sun bear is named so for its characteristic orange- to cream-coloured, crescent-like chest patch. The generic name Helarctos comes from two Greek words: (, related to the sun) and (, bear). Another name is honey bear, in Malay and Indonesian, in reference to its habit of feeding on honey from honeycombs. "Honey bear" can also refer to the kinkajou.
Taxonomy and phylogeny
The scientific name Ursus malayanus was proposed by Stamford Raffles in 1821; he first described a sun bear from Sumatra. In 1825, Thomas Horsfield placed the species in a genus of its own, Helarctos, when describing a sun bear from Borneo.
Subspecies and distribution
H. annamiticus, described by Pierre Marie Heude in 1901 from Annam, is not considered a distinct species, but is subordinated as a junior synonym to H. m. malayanus. In 1906, Richard Lydekker proposed another subspecies by the name H. m. wardii for a sun bear skull, noting its similarities to a skull from Tibet with a thicker coat, but the Tibetan specimen was later found to be an Asian black bear (Ursus thibetanus). Genetic differences between the two subspecies are obscure. It is considered to be monotypic.
Phylogeny
The phylogenetic relationships among ursid species have remained ambiguous over the years. Noting the production of fertile hybrids between sun bears and sloth bears (Melursus ursinus), it was proposed that Helarctos be treated as a synonym of Melursus. However, studies differed on whether the two species were closely related. A 2007 phylogenetic study gives the relationships of the sun bear with other species of Ursidae based on complete mitochondrial DNA sequences as shown in the cladogram below. The brown bear/polar bear genetic lineage was estimated to have genetically diverged from the two black bears/sun bear lineage around (mya); the sun bear appears to have diverged from the two black bears between 6.26 and 5.09 mya. and 5.89–3.51 mya. Nuclear gene sequencing of bear species revealed that the sloth bear and the sun bear were the first Ursinae bears that radiated and are not included in the monophyletic Ursus group; moreover, all relationships between the bears were well resolved.