Slow loris density in a fragmented, disturbed dry forest, north-east Thailand

Primate survival in disturbed forests can be governed by a complex of forest variables. For nocturnal arboreal primates, determining these ecological features is notoriously difficult but is critically important for their conservation. Here we assessed the effects of forest type, food availability, human disturbance, and forest structure on the nocturnal Bengal slow loris (Nycticebus bengalensis) in Sakaerat Biosphere, north-east Thailand, a small disturbed fragment containing dry evergreen, dry dipterocarp, and plantation forests. Distance sampling revealed plantation forest had the highest density estimate (27 loris/km² ) followed by dry evergreen forest (17 loris/km² ), while dry dipterocarp forest only had four detections. Based on forest type selection analyses, loris had a positive association with sap and fruit-flower productivity which was highest in plantation forest compared to the natural dry evergreen or dry dipterocarp forests. Furthermore, forest structure selection analysis indicated loris preferred denser canopies. Loris presence was positively associated with canopy height, canopy connections, tree trunk vegetation cover, and canopy density. The higher loris density found in the plantations, as also reported by other studies, was associated with dense vegetation structure and higher food productivity, particularly sap. However, the important structural features found in the plantation forest are strongly dependent on forest maturity, and the reduced longevity of such exotic tree species may limit the conservation importance of plantation forest, merely acting as a short-term alternative to natural habitat.