Bornean sun bear, Helarctos malayanus euryspilus Horsfield, 1825 of Borneo

The sun bear is the smallest and best adapted to a tree-dwelling lifestyle within the Ursidae. Sun bears are nocturnal, during the day they sleep in the trees, around 2 to 7 metres above the ground – they break or bend branches to make a nest or a viewing platform. The systematic classification of the Sun bear is highly controversial. While some classification systems place it in the genus Ursus (which also includes baribals, brown bears, polar bears and ruffed bears), it is usually categorised in its own genus, Helarctos.

There are two subspecies. H. m. malayanus from Sumatra and the Southeast Asian mainland and the slightly smaller form H. m. eurypsilus from Borneo.