Activity Budget and Postural Behaviors in Orangutans on Bukit Merah Orang Utan Island for Assessing Captive Great Ape Welfare.

Assessments of the welfare status of captive and semi-captive animals often compare how their expression of natural behaviors differs from that of free-ranging conspecifics. From December 2015-2016, we recorded and analyzed the activity budget and postural behaviors of three orangutans in Bukit Merah Orang Utan Island (BMOUI) to evaluate their welfare status. The orangutans' activity budget was dominated by resting (60%), feeding (13%), playing (14%), and moving (9%). Behavioral categories followed a similar trend: resting > feeding > moving > playing, except that the subadult male spent significantly more time playing than the two adults. The most predominant posture was sitting (47.0%), followed by pronograde standing (29.4%), lying (10.5%), and clinging (4.5%). Our results suggest that orangutans on BMOUI engage in less feeding but more resting, and show less postural diversity than free-ranging individuals. We propose that appropriate interventions to shift activity budgets, especially feeding vs. resting, and postural behaviors of captive orangutans toward those found in free-ranging orangutans might be beneficial for their welfare and survival.