Fatality of a wild Bornean orangutan ( Pongo pygmaeus morio ): behavior and death of a wounded juvenile in Danum Valley, North Borneo

Reports of wild great ape fatalities have been very limited, and only two have described wild orangutan deaths. We found a wounded juvenile female Bornean orangutan on 7 October 2006 in the Danum Valley, Sabah, Malaysia, and observed the individual’s behavior for 7 days until her death on 13 October 2006. The 5–6-year-old orangutan, which we had observed since 2004, was wounded in the left brachium, back, and right hand. The individual’s behavior changed after injury; the mean nest–nest active time became significantly shorter than before injury (from 12 h 3 min to 9 h 33 min), the mean waking time became significantly later (0552–0629 hours) and the mean bedtime became significantly earlier (from 1747 to 1603 hours). In the activity budget, resting increased significantly from 28.0 to 53.3%. Traveling and feeding decreased significantly from 23.5 to 12.7% and from 45.6 to 32.8%, respectively. The rate of brachiation during traveling and nest making decreased, whereas ground activity increased from 0 to 9%. We observed one vomiting incident and four occurrences of watery diarrhea during the 7 days before the individual died. The results of an autopsy performed by a local veterinarian suggested that the cause of death was septicemia because of Pseudomonas aeruginosa infection of the severely contaminated wounds. The morphology and distribution of the wounds suggested they had been incurred during an attack by a large animal with fangs and/or claws. This juvenile female became independent of its mother at ~4–5 years of age, slightly earlier than average. This individual might have been vulnerable to predatory attack because of her small body size (~5 kg at death) and lack of the mother’s protection.