Abstract
Tool-using behavior entailing honey fishing was investigated in free-ranging juvenile rehabilitant orangutans (Pongo pygmaeus pygmaeus). A bottle containing honey was attached to a tree in a forest where the rehabilitant orangutans were re-introduced. The honey bottle had a hole 1 cm in diameter. A total of 23 orangutans approached the bottle during 10 30-min sessions. Out of these individuals, 15 orangutans inserted materials such as twigs and leaf stalks, or oriented these materials to the honey bottle hole. The following characteristics could be observed. First, two individuals made tools by breaking off branches from trees. Second, ten individuals modified materials by removing side branches or shortening twigs. Third, the orangutans used already detached objects by picking them up from the ground in most of the cases. In addition, the youngest individual who used tools was 3 years old. These characteristics are similar to those of tool use by chimpanzees, the most skillful tool users among great apes in the wild. The present study confirms that orangutans have the potential capacity for skillful tool use despite its infrequently observed occurrences in the wild.
