Orangutan leaf-carrying for nest-building: Toward unraveling cultural processes

Abstract

We report an empirical study on leaf-carrying, a newly discovered nest-building technique that involves collecting nest materials before reaching the nest site. We assessed whether leaf-carrying by rehabilitant orangutans on Kaja Island, Central Kalimantan, owes to cultural influences. Findings derive from ca 600 h observational data on nesting skills and nesting associations in Kaja's 42 resident rehabilitants, which yielded 355 nests and 125 leaf-carrying cases by 34 rehabilitants. Regional contrasts with 14 other communities (7 rehabilitant, 7 wild) indicated cultural influences on leaf-carrying on Kaja. Association data showed exceptional social learning opportunities for leaf-carrying on Kaja, with residents taking differential advantage of these opportunities as a function of development, experience, and social position. Juvenile males with basic nesting skills were most influenced by social input. Most (27) leaf-carriers had probably learned leaf-carrying when caged and 7 probably learned it on Kaja. Social priming was probably the main impetus to leaf-carrying on Kaja, by simply prompting observers to copy when leaf-carrying associates collected nesting materials, what they collected, and where they used their collected materials. Implications concern acquisition processes and ontogenetic schedules that orchestrate sets of features-needs or interests, cognitive abilities, social preferences-which enable cultural transmission.

Nest-building orangutans demonstrate engineering know-how to produce safe, comfortable beds

“…Therefore, it seems that orangutans detach preferred branches for the lining of their nest structures. The choice of appropriate material from different trees for the purposes of nest lining has previously been described in leaf-carrying behaviors, whereby orangutans select lining materials from other locations and carry them to the nest site (12,20). Therefore, it is possible that a choice for smaller, weaker, and more flexible branches is being exhibited by nest-building orangutans at Ketambe.…”

“…Previous research into orangutan nests can be broadly broken into two major avenues of investigation: one, focusing on nestbuilding behavior (3,(9)(10)(11)(12); and the other, concentrating on the use of nests to predict population numbers and distribution (3,10,15,16). Investigations into nest-building behavior have provided detailed, insightful, and descriptive knowledge of the basic nest-building process.…”

“…Investigations into nest-building behavior have provided detailed, insightful, and descriptive knowledge of the basic nest-building process. Such data have mostly comprised observations of nest building, such as the frequency and duration of builds, positioning of nests, and preferences within the ritual of nest building (3,(9)(10)(11)(12). The study of nests to understand populations of wild orangutans has led to knowledge of nest longevity and geographical distribution (3,10,15,16).…”

“…Construction usually follows a basic pattern (3,11,12). After choosing a nest location on a lateral branch, or branches, the orangutan will bend and break branches inward toward a central point, weaving and twisting the branches to lock them into the basic nest structure.…”

“…Leafy branches are detached, usually from the surrounding area, and placed on top of the base structure as a lining. Extra features, such as a roof, "pillow," or "blanket," are then constructed and added if required by the individual (3,11,12). Orangutan nests have been described as sturdier, more complex and elaborate, and as lasting longer in the forest canopy, than those of African apes (2,10).…”