Fragmented populations of the Vulnerable eastern hoolock gibbon Hoolock leuconedys in the Lower Dibang Valley district, Arunachal Pradesh, India K ULADIP S ARMA,MURALI K RISHNA and A WADHESH K UMAR Abstract We conducted a survey of the distribution and (Lwin et al., ). The genus Hoolock comprises two distinct population status of the eastern hoolock gibbon Hoolock species, the eastern hoolock gibbon Hoolock leuconedys and leuconedys in non-protected fragmented forest areas of the the western hoolock gibbon Hoolock hoolock, which are sep- Lower Dibang Valley district of Arunachal Pradesh, India, arated based on differences in fur coloration (Mootnick & during September –June . We estimated the mini- Groves, ; Geissmann, ). H. leuconedys was mum population density at seven study sites by direct obser- known to be distributed east of the Chindwin River to the vation and by counting the number of vocalizations heard Salween River in Myanmar and south-west Yunnan from groups that were out of view. We used -ha belt trans- Province in China, at ,–, m altitude (Groves, ), ects ( × m) to estimate tree diversity in the study area. until it was observed in Arunachal Pradesh, India, between For two groups of gibbons we recorded their feeding pat- the Lohit River in the north and the mountains of Dafa Bum terns in forest fragments, using focal individual sampling, in the south (Das et al., ). More recently the species has during May . A total of groups and three solitary been found in Sadiya Division, the easternmost part of individuals were recorded: groups and three individuals Assam, south of the Dibang–Brahmaputra River system through visual encounter and groups through vocal- (Chetry & Chetry, ). The population, distribution, eco- ization recognition. The mean group size recorded was logy and behaviour of the western hoolock gibbon have been . ± SE . (range –). We counted a total of trees, studied in India and Bangladesh by Alfred & Sati (), Das of species and families, in belt transect surveys cov- et al. (), Mukherjee () and Islam & Feeroz (). ering all non-protected fragments of the Lower Dibang Preliminary studies have been conducted on the eastern Valley district. The gibbons’ diet consisted of seasonal fruits hoolock gibbon to explore its distribution and population and figs (%), leaves (%), seeds (%) and flowers (.%). status in Arunachal Pradesh and Assam, India (Chetry The major threats recorded at the study sites were habitat et al., , ; Chetry & Chetry, ). Population sur- destruction and hunting. To protect the Vulnerable eastern veys of the eastern hoolock gibbon have also been conducted hoolock gibbon, conservation measures will need to involve in China (Fan et al., ) and Myanmar (Brockelman et al., local communities. ; Walker et al., ). The eastern hoolock gibbon is ca- tegorized as Vulnerable on the IUCN Red List (Brockelman Keywords Conservation status, distribution pattern, east- & Geissmann, ) and listed as a Schedule I species in the ern hoolock gibbon, fragmented population, Hoolock leuco- Indian Wildlife (Protection) Act, . To inform future nedys, India, Lower Dibang Valley conservation and management planning we carried out a This paper contains supplementary material that can be survey of the fragmented forest areas of the Lower Dibang found online at http://journals.cambridge.org Valley district, Arunachal Pradesh, India, to determine the current population and conservation status of H. leuconedys in this region. Introduction Study area oolock gibbons (genus Hoolock) occur in forested Hareas of north-east India, Bangladesh, Myanmar The study was conducted at seven sites outside Mehao and southern China (Harlan, ; Groves, ). Wildlife Sanctuary, in Arunachal Pradesh (Fig. ): six sites Geographically the natural range of these apes extends to the south-east and north-west of the Sanctuary (Injuno, from the Brahmaputra River east to the Salween River Koronu, Delo, Hawaichapori, Horupahar, Iduli) and one site to the north-west (Chidu). These seven study sites lie KULADIP SARMA,MURALI KRISHNA and AWADHESH KUMAR (Corresponding author) within two administrative circles in the Lower Dibang Wildlife Research and Conservation Laboratory, Department of Forestry, North Valley district: Koronu Circle and Roing Circle. The study Eastern Regional Institute of Science and Technology (Deemed University), sites are at – m altitude and are unclassified forests, Nirjuli-791109 (Itanagar), Arunachal Pradesh, India E-mail [email protected] not included in any management class and under the juris- Received April . Revision requested July . diction of the territorial forest officer. The main forest types Accepted August . First published online September . recorded in the area are low hills and plains semi-evergreen © 2014 Fauna & Flora International, Oryx, 49(1), 133–139 doi:10.1017/S0030605312001299 Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.139, on 02 Oct 2021 at 08:53:59, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605312001299 134 K. Sarma et al. FIG. 1 The distribution of eastern hoolock gibbons Hoolock leuconedys and forest patches in the study area, in the Lower Dibang Valley district, Arunachal Pradesh, India. forest, Assam alluvial plains semi-evergreen forest B/CIa directly from the transect and after following their calls and sub Himalayan light alluvial evergreen forest B/CI/ (Kakati et al., ). We tried to locate all calling groups es- ISI (Champion & Seth, ; Kaul & Haridasan, ). timated to be , m from the trail. For direct sightings we The study area is occupied by the Idu-Mishmi and Adi peo- also recorded the local vegetation type and the degree of ples, who generally depend on agriculture for their liveli- human disturbance of the habitat. We used stratified ran- hood. They cultivate cash crops such as ginger Zingiber dom sampling of transects to collect tree data within , officinale, maize Zea mays, mustard Brassica juncea and × m( ha; Sykes & Horrill, ; Kumar et al., ). We rice Oryza sativa. established the transects along existing forest trails and foot- paths and recorded the local names and girth of all trees $ Methods cm in girth at breast height. We estimated the minimum distance between gibbon The survey was conducted from September to June groups, using the Distance Matrix tool in QGIS (QGIS, . We estimated the minimum population, based on vis- ). Using the geographical information system map we ual encounters and auditory data, and recorded group size calculated the distance from each group to the nearest forest and age-class compositions (Kakati et al., ). We cate- patch to examine the effect of forest degradation on group gorized individual gibbons as adult, subadult, juvenile or size. We counted the number of trees in the patches where infant, based on body size and coat colour (Gupta et al., gibbons were located, and assigned each patch to one of the ; Table ). following categories: single tree, single tree in bamboo patch, We covered a total of km during census walks – trees, – trees, and . trees. We compared the mean across the seven study sites (Table ). We sighted gibbons group size among the different categories. We analysed the © 2014 Fauna & Flora International, Oryx, 49(1), 133–139 Downloaded from https://www.cambridge.org/core. IP address: 170.106.40.139, on 02 Oct 2021 at 08:53:59, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605312001299 Eastern hoolock gibbon in India 135 TABLE 1 Distinguishing characteristics of male and female eastern (%) adult females, (%) subadult males, (%) hoolock gibbons Hoolock leuconedys in different age categories subadult females and (%) infants (Table ). (Gupta et al., ). The mean group size across the seven study sites was . ± – Age category Sex Distinguishing characteristics SE . (range ). For individual sites the highest mean Infants 1 day–2 Male & 20–35 cm length; carried by group size was . (Koronu, Injuno, Hawaichapori and years old female adult female; white to light grey Chidu) and the lowest was . (Horupahar). There was a (, 1 year), dark grey or black statistically significant difference in the group size and (1–2 years old); cannot determine encounter rate across the seven sites (Friedman test, sex in the field χ = ., P = .,n=). The ratio of immature (infant – – Juveniles 2 4 Male & 35 44 cm length; black; distinct and subadult) to adult gibbons was the same at all sites. years old female eyebrows; never carried by mother; Group size also varied with habitat quality, specifically the sleep away from mother – – number of standing trees (Fig. ). Larger groups were Subadults 4 7 Male 45 52 cm length; jet black; emer- years old ging scrotum found in forest patches ( . ) than in single trees ( . ). The Female Broad greyish patches on a black distance of the group from the nearest forest patch also in- coat fluenced the group size; smaller groups (.) were found at Adults . 7 Male Distinct scrotum and jet black coat distances . m(Fig. ). years Female Buff-coloured coat The estimated male : female ratio among adults was . : across the seven study sites. The infant : female ratio was highest in the Injuno area (. : ; Table ). change in forest cover, using satellite images of the study The recording of gibbons in Horupahar and area from and , with ERDAS Imagine v. Hawaichapori was significant because both these fragmen- (Intergraph,