Orangutans Plan Their Journeys the Night Before.

In 2009, Carel van Schaik at the University of Zurich published findings from years of field observation in Sumatra that quietly upended a long-held assumption about great ape cognition. Every evening, before settling to sleep in their night nests, male Bornean and Sumatran orangutans would call out in a specific direction. The calls, known as long calls, carry through dense forest for up to a kilometer. And the direction they called, van Schaik’s team found, predicted the direction the orangutan would travel the following morning with statistically significant accuracy.

The orangutans were announcing their travel plans the night before executing them. Not to navigate. Not to find food in the moment. They were broadcasting future intentions, which requires holding a representation of a future state in mind and communicating it to others. That is a cognitive capacity that, until relatively recently, was considered uniquely human.

The Forest Person

The word orangutan comes from the Malay words orang, meaning person, and utan, meaning forest. Forest person. The people who named them were not being poetic. They were being observational. An orangutan moving through the forest canopy, using its hands and feet with equal dexterity, pausing to examine objects, solving problems, and apparently planning its route, looks like a person navigating a familiar landscape.

Pongo pygmaeus, the Bornean orangutan, and Pongo abelii, the Sumatran orangutan, are the most distantly related of the great apes to humans, having diverged from the human lineage approximately 12 to 14 million years ago. Despite this greater evolutionary distance, they share with humans a set of cognitive capacities that chimpanzees and gorillas, our closer relatives, do not always demonstrate as clearly.

Tool use in orangutans is extensive and varied. Wild Sumatran orangutans use sticks to extract insects from tree holes, use leaves as gloves when handling spiny fruits, and fashion rain hats from large leaves held over their heads during downpours. These behaviors are not universal across all orangutan populations. They vary between groups in ways that indicate cultural transmission rather than independent invention, with specific tool-use traditions maintained within populations and absent in neighboring ones.

Researcher Michael Krützen at the University of Zurich has mapped the distribution of tool-use traditions across Sumatran orangutan populations and found that the pattern of cultural variation correlates with social contact between groups rather than with environmental differences. Populations that have more contact with each other share more cultural traditions. Populations separated by rivers or other barriers have diverged culturally. It is the same pattern seen in human cultural variation, operating in a great ape.

Solitary but Not Simple

Orangutans are the most solitary of the great apes. Adult males in particular spend most of their time alone, coming into contact with females primarily for mating and maintaining large, overlapping home ranges through their long calls. The solitary lifestyle has sometimes been interpreted as evidence of limited social complexity, but this interpretation has been substantially revised by long-term field research.

Females with dependent offspring form the stable social units of orangutan society. A female raises a single offspring for seven to eight years, the longest period of maternal dependence of any non-human animal, during which the offspring learns the forest, its food sources, its seasonal patterns, and its tool-use traditions from its mother. The extended dependency is not a cost of slow development. It is the mechanism by which cultural knowledge is transmitted across generations.

Birute Galdikas, who has studied Bornean orangutans at Camp Leakey in Kalimantan since 1971 in one of the longest continuous wildlife studies ever conducted, has documented individual orangutans across multiple decades, tracking the transmission of behavioral traditions from mothers to offspring and observing how individuals navigate the complex social landscape of overlapping ranges and occasional encounters.

Her observations, combined with van Schaik’s cognitive research, paint a picture of an animal whose apparent simplicity, the solitary life, the slow reproduction, the quiet movement through the canopy, conceals a cognitive and social complexity that took decades of careful observation to reveal.

Two Species, Both Critically Endangered

Both orangutan species are listed as Critically Endangered on the IUCN Red List. The Bornean orangutan population has declined by more than 50% over the past 60 years. The Sumatran orangutan, with a total wild population of approximately 14,000 individuals, is one of the rarest great apes on Earth. A third species, the Tapanuli orangutan, Pongo tapanuliensis, was described only in 2017 and has a total population of fewer than 800 individuals, making it the most endangered great ape and one of the most endangered mammals of any kind.

The primary driver of decline is deforestation for palm oil, timber, and agricultural expansion. Orangutans require large areas of intact forest. They cannot survive in degraded or fragmented habitat at viable population densities. As forest cover in Borneo and Sumatra has been reduced by an estimated 80% over the past century, orangutan populations have contracted accordingly.

An animal that plans its journeys the night before, that transmits cultural knowledge across generations through eight years of maternal teaching, that has been called the forest person by the people who have lived alongside it for centuries, is being displaced by palm oil plantations at a rate that conservation efforts have not been able to match.

Van Schaik’s orangutans still call out their travel plans each evening in the forests that remain. There are just far fewer forests left to call across.