Distribution and Habitat The P. bicolor is distributed between the Indragiri River and the Batanghari River of central Sumatra (Aimi & Bakar 1992; Anandam et al. 2013; Beausejour et al. 2021). All of our records are recorded within this range (Fig. 1 and Table 1). Based on our observations (localities number 13 to 27 in Fig. 1 and Table 1), the P. bicolor is found in the rubber plantations Hevea brasiliensis (Euphorbiaceae) in lowland habitats (Figs. 4 - 5). Groves (2001) suggest P. bicolor is a montane form, with three skins reported in the Leiden Museum from north Kerinci by Hooijer (1962), which are variants of this species grading toward P. melalophos. However, north Kerinci is not located between the Indragiri River and Batanghari River, and based photo of Presbytis in Kerinci Mountain (Beausejour et al. 2021), it is likely refer to P. m. nobilis. Further references reported P. bicolor inhabits highlands or montane forest habitats (Anandam et al. 2013; Supriatna 2019; Beausejour et al. 2021), but their map for the distribution range of P. bicolor did not reach the highlands zone of Bukit Barisan Mountain range in Sumatra. Based on the available information (Table 1), the highest area where P. bicolor was recorded is the Sijunjung District, which has the highest elevation of this area c. 902 m (Mapcarta 2022). Whitten et al. (2000) classified the average elevation of the forest zones in Sumatra range 0 - 1.200 m as lowland habitats. According to Nijman (2021), P. bicolor inhabits lowland and hill forests. Nijman (2021) summarized some additional localities for P. bicolor, including concession areas of the forest plant industry of Riau Andalan Pulp and Paper or RAPP (Riau Province), Rimbang Baling Wildlife Sanctuary (Riau Province), and Bukit Bungkuk Strict Nature Reserve (Riau province). All of these areas are located in the northern part of Sumatra, across the Indragiri River (between Kampar River and Indragiri River, not Indragiri River and Batanghari River). Further investigation suggests that species recorded in Rimbang Baling Wildlife Sanctuary and Bukit Bungkuk Strict Nature Reserve as P. siamensis; and species found in Bukit Bungkuk as P. femoralis (Bugiono 2001; LPPM-IPB 2015; Lathifa et al. 2016; Prayogi & Atmoko 2016; Yasir & Sutrisno 2019). The P. bicolor has been reported to occur in Bukit Dua Belas National Park (Supriatna 2019; Beausejour et al. 2021), but this still needs further confirmation because the park is located across in southern part of Batanghari River (between the Batanghari River and Musi River). Furthermore, Setiawan (2017) reported three primates (P. melalophos, Agile Gibbon Hylobates agilis and Siamang Symphalangus syndactylus) from Bukit Bulan, Bukit Dua Belas National Park, without information for P. bicolor. Records of P. bicolor in forested areas (Bukit Tiga Puluh National Park, Figs. 6 - 7) and various habitats, such as plantations and near urban areas, suggest this primate can survive in disturbed habitats. Supriatna (2019) reported that P. bicolor found in primary forest and secondary hill rainforest, shrub or secondary growth, and plantations, considered this species to be tolerant of habitat changes. In Jambi Province, we found remaining secondary forest and old rubber plantations provide suitable habitats for P. bicolor for feeding and roosting (Figs. 2 - 11). The P. bicolor was presumed a forest-dependent species, and the conversion of forests for various purposes (particularly large-scale plantation) have been given impacted on the loss of habitat. Our survey in Jambi Province revealed that this species is tolerant to degraded forest, and also survive in the human-modified habitats, such as rubber plantation or agricultural scale of local people. However, we fail to spot P. bicolor in the Industrial Timber Plantation (locally called Hutan Tanaman Industri or HTI), of the Eucalyptus plantation. It is likely P. bicolor avoided Eucalyptus trees. Behaviour The P. bicolor is diurnal, arboreal, moves quadrupedally in trees and lives in groups of between 8 to 12 individuals consisting of both females and males (Supriatna 2019). Our observation found there are few groups consisting of up to 15 and more than 20 individuals. On a few occasions, we also found single or two individuals, suggesting they usually live in solitary. Like many other primate species, surilis emit loud, conspicuous vocalizations termed loud calls or long-distance calls (Meyer et al. 2011). Based on our observations, P. bicolor is commonly silent (Fig. 6), but when their feel disturbance, at least one of them in the group will prepare a voice that we assume as an early alarming call (Fig. 7). On one occasion, we have observed their response with noisy calls when a drone flew around them. Diet and Feeding Ecology The P. bicolor is known to be folivorous or leaf-eating but has also been seen to consume fruit, flowers, seed and some species of small insects (Anandam et al. 2013; Supriatna 2019; Nijman 2021). Further details of diets are lacking. During field visits, We were observed P. bicolor consuming leaves of Para rubber tree Hevea brasiliensis (Euphorbiaceae) and Mango Mangifera sp (Anacardiaceae) (Figs. 8 - 11). Local people reported that P. bicolor was observed consuming some agricultural plants, including leaf of Cassava Manihot esculenta (Euphorbiaceae), the leaf of Chili Capsicum annuum (Solanaceae), the young fruit and seed of Para rubber tree, the leaf and fruit of Jengkol Archidendron pauciflorum (Caesalpinioideae), the fruit of Mangosteen Garcinia mangostana (Clusiaceae) and fruit of Psidium guajava (Myrtaceae). Even though P. bicolor fed the plants of the local people, but this species reported does not cause severe economic damage, such as Long-tailed macaque Macaca fascicularis and Southern pig-tailed macaque Macaca nemestrina. Supriatna (2019) reported P. bicolor has been seen on the ground where they access food and water. On one occasion, we observed P. bicolor go down to the ground, possibly searching for suitable food (Fig 12). Furthermore, we saw this species escaping to avoid disturbance, crossing the road from old palm oil vegetation to dense rubber vegetation (Fig. 14).
