Pongo abelii

Primarily arboreal and largely solitary, adult males and females maintain overlapping home ranges rather than large cohesive troops; social encounters occur at fruiting trees or between mothers and dependent offspring. They are highly intelligent—use tools (sticks, leaves), build complex sleeping nests nightly, communicate with long calls (males) and soft vocalizations, and show cultural variation in foraging and tool use across populations.

Females begin reproducing relatively late and have long interbirth intervals (commonly 6–8 years), reflecting intensive maternal care; gestation is about 8–9 months and usually produces a single infant. Young remain dependent for several years as they learn foraging, nest building, and social skills from their mothers, which contributes to slow population recovery.

Sumatran orangutans have extremely long arms, curved hands and feet for suspensory locomotion, and strong grip strength; sexually mature males may develop cheek pads (flanges) and throat sacs used in visual and acoustic display. Their diet is dominated by ripe fruit but includes leaves, bark, insects and occasionally bird or mammal prey; lifespan in the wild typically reaches 30–45 years.

Endemic to northern Sumatra, these orangutans historically occupied continuous lowland and hill forests; escalating logging, agricultural expansion (notably oil-palm), road building and hunting since the 20th century have fragmented and reduced their habitat. Scientific study and conservation interest grew in the late 20th century as declines accelerated, prompting rescue/rehabilitation and protected-area efforts.

Pongo abelii is classified as Critically Endangered due to rapid habitat loss, fragmentation, illegal capture, and human–wildlife conflict; populations are small, fragmented and declining in many areas. Conservation priorities include protecting and reconnecting forest tracts, stricter law enforcement against hunting and illegal land conversion, community-based conservation, and continued rescue, rehabilitation and carefully managed reintroductions.