Activity Budgets and Boldness as Potential Predictors of Release Readiness in Rehabilitating Javan Slow Lorises

Abstract Rehabilitation centers are central to the conservation of Javan slow lorises ( Nycticebus javanicus ) by providing care for individuals confiscated from trade and preparing them for potential release. To evaluate behavioral readiness for reintroduction, we quantified activity budgets and boldness in 10 adult N. javanicus (7 females and 3 males) housed at a rehabilitation facility in West Java, Indonesia, from May to September 2024. Locomotion dominated activity budgets (57.14% ± 24.86%), followed by resting (23.51% ± 16.61%), with low rates of stereotypy (4.36% ± 13.48%) and grooming (2.33% ± 5.28%). Boldness tests using six novel object types revealed strong stimulus dependence: predator models suppressed approach, while enrichment and neutral objects encouraged exploration. Sex, housing conditions, and rehabilitation duration did not predict boldness, indicating inter-individual differences in responses to novelty. Principal component analysis identified an integrated bold–exploratory activity axis, suggesting that activity budgets and boldness covary as part of a behavioral syndrome rather than independent traits. Together, these results indicate that combined activity and personality metrics provide complementary indicators of behavioral welfare and release readiness, with potential to improve pre-release assessment and site matching for this critically endangered primate.