Western Purple-faced Langurs (Semnopithecus vetulus nestor) Feed on Ripe and Ripening Fruits in Human-modified Environments in Sri Lanka

Abstract

Although most colobines feed mainly on leaves and a few feed heavily on seeds, colobine digestive adaptations for folivory are thought to preclude the high use of ripe fleshy fruits. In this long-term study of Semnopithecus vetulus nestor, the endemic western purple-faced langur of Sri Lanka, I investigated the feeding ecology and dietary flexibility for fruit feeding in 2 free-ranging groups (PT1 and R1) living in human-modified environments with abundant cultivated fruit, at Panadura and Piliyandala, for 19 mo and 13 mo respectively, using scan-sampling, vegetation enumeration, and phenological studies. In contrast to folivorous forest-living colobines, including other subspecies of Semnopithecus vetulus, my focal groups used more fruit (>50%) than foliage (PT1: 36%; R1: 34%). Both groups used many plant species (PT1 115; R1 59), but selected their food species, fruits over leaves, and young leaves over mature leaves. Fruit use was independent of young leaf availability. Notably, 78.4% and 83.4% of fruits consumed by PT1 and R1 were fleshy and human-edible, most of which were ripening or ripe (PT1: 72.4%; R1: 94.8%). The main fruit for both groups was Artocarpus heterophyllus (Moraceae; jakfruit), a cultivar with fleshy fruit. These findings differ from previous understanding of colobine diets. I suggest that environmental factors, such as the abundance and nature of available fruits, and the absence of arboreal-primate fruit competitors, could influence the use of ripe fleshy fruits by colobines strongly, highlighting the need to review the dietary and digestive flexibility of this group in changed and changing natural environments to formulate effective conservation action.