Some interfacing enclosures in the subdivision of great apes are occupied by orang-utans (PONGO PYGMAEUS) (PONGIDAE). The word "orang-utan" in Malaysia means "the forest man ". It is one of the largest apes (in males body weight is up to 100 kg, body length is about 150 sm., the arms have 2,25 m in length). Adult weight for females is estimated up to 40-50 kg. Orang-utans have short and relatively weak legs and powerful hands and arms, designed to live on trees.

Average brain size in orang-utans is 411 sm3. Their brain resembles the human one. The species is arboreal and diurnal. They normally move through trees by climbing and walking. When on the ground orang-utans are very vigilant moving quadrupedally without any hurry. Daily movement cover the distance of not more than 1 km, sometimes 200-300 meters. Terrestrial movement is more typical for adult males as they are larger and more powerful. Orang-utans construct large platform nests for night-time and sleep there. Animals usually occur in pairs, in small family groups or alone. Some observations indicate that adult males are very aggressive to each other. They live alone and meet with females only for mating.

The diet includes fruits, leaves, as well as insects, small vertebrates and birds' eggs. Orang-utans drink water from trees' hollows, lick it off from fur and eaves. These apes are intelligent. Tool use by wild orang-utans has been reported for digging, eating and some other purposes. Gestation in females of orang-utan lasts 9 months. There is a singe young, twins occur very rare. Average birth weight is approximately 1,5 kg. The young stay with mother for about 4 years. The interbirth intervals are 6 years. Orang-utans' females are very careful mothers and the mortality of their youngs is very low.

An adult male of orang-utan usually occupies home range of about 1-5 sq.km, which overlaps home ranges of several females. Adult males older than 30 years are still dominants but don't take part in breeding. Now orang-utans are found only on the islands of Sumatra and Borneo. The species is classified as endangered and is on appendix 1 of the CITES. The problem is to stop illegal export of orang-utans and prevent further destroying of their habitats. In captivity orang-utans are kept and bred successfully enough. In the Moscow Zoo the first offspring was born in 1980. The estimated live-span in captivity is nearly 50 years.