Fragmented Populations of the Vulnerable Eastern Hoolock Gibbon Hoolock Leuconedys in the Lower Dibang Valley District, Arunachal Pradesh, India

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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: 170.106.33.22, on 01 Oct 2021 at 14:42:10, 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: 170.106.33.22, on 01 Oct 2021 at 14:42:10, 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, Madison, USA). We recorded the feeding and ted forest patches are surrounded by agricultural lands and ranging patterns of two gibbon groups, A and B, collecting human habitation, leaving gibbons more vulnerable at these data on various aspects of food and feeding for each group sites. There was a significant correlation between the for  consecutive days in May . We recorded observa- encounter rate and the size of the study area (Mann- tions every  minutes, with focal individual sampling Whitney U, Z = .,P, .,n=); furthermore, a higher (Altmann, ). Each group comprised one adult male encounter rate was observed when the mean distance and one adult female with an infant. We recorded the between sites was lower (Fig. ). time spent by each individual on each food plant, and the In the  transects we counted  trees, of  species ( parts eaten, along with the time spent at different feeding identified to species) and  families (Supplementary sites (trees, climbers and crops). Plant parts were categor- Table S). The most common species were Ficus spp., fol- ized as young leaves, mature leaves, fruits/figs, flowers and lowed by Ailanthus grandis and Bischofia javanica. The seeds. The groups were habituated to the presence of hu- least frequently observed species was Bombax ceiba. mans. We followed them from dawn to dusk each day. Satellite images of the study area for – show that We focused on each adult in turn, to ensure representation the loss of forest cover was mainly as a result of the expan-  of all members of the group. We used SPSS v. . (SPSS, sion of agricultural land, which increased by %( km ). Chicago, USA) for statistical analysis, using Friedman and In the study area a % decrease in forest cover was docu- Mann–Whitney U tests to examine the differences in mented during – (Table ). encounter rates and mean group sizes between the seven Based on the total feeding time during a -day study per- study sites. iod, the diet of the two focal groups of gibbons consisted of fruits and figs (%), leaves (%), seeds (%) and flowers (.%). Gibbons showed a preference for young leaves   Results ( %) over mature leaves ( %). The main threats recorded at the study sites, through We estimated the total number of groups from the number general observation and interaction with local people, of visual encounters and the vocal data. A total of  groups were habitat destruction and hunting by local people. and three solitary individuals were recorded. The maximum Habitat destruction was caused mainly by expansion of per- number of groups was recorded at Iduli (), followed by manent agricultural practices, shifting cultivation, tea plan- Delo (), Horupahar (), Koronu (), Chidu (), Injuno () tation, and construction of a national highway and and Hawaichapori (). Of the  groups/individuals en- permanent settlements. The eastern hoolock gibbon is countered directly,  groups were recorded in the Koronu hunted mainly as an alternative source of meat, and its Circle and four groups in the Roing Circle, at Chidu. bones, skin and fur are used for decoration and for making A total of  individuals in  groups and including  bags. Domestic dogs Canis lupus familiaris kept by local solitary individuals were recorded:  (%) adult males, people to protect their property and livestock are potential

TABLE 2 Survey data from seven study sites in fragmented forest areas of Lower Dibang Valley district, Arunachal Pradesh, India (Fig. ).

Variables Chidu Injuno Horupahar Hawaichapori Delo Koronu Iduli Altitude (msl) 390–430 211–283 195–215 198–216 209–251 212–259 151–179 Area of forest (km2) 0.25 0.91 2.32 3.50 4.24 6.97 15.26 No. of survey days 4 4 5 2 5 5 8 Length of transect walked (km) 16.0 13.5 14.0 19.0 19.5 15.0 12.0 No. of groups encountered (G) 2 3 5 1 6 4 7 No. of solitaries encountered (S) 0 1 1 0 1 0 0 No. of groups heard/seen 2 0 3 0 1 1 4 Encounter rate (G+S per km) 0.13 0.22 0.35 0.05 0.30 0.26 0.58 Total no. of individuals 21 23 15 3 10 32 12 No. of adult individuals Male 8 8 5 1 4 11 4 Female 7 8 4 1 3 10 4 No. of subadult individuals Male 3 3 3 0 1 7 2 Female 0 0 0 0 0 3 0 No. of infants 3 4 2 1 2 4 2 Immature*/adult ratio 2.0 2.0 2.2 2.3 2.5 2.0 1.9 Infant/female ratio 0.50 0.67 0.50 1.00 0.43 0.40 0.40 Mean group size (No. of groups) 3.00 (4) 3.00 (3) 2.75 (8) 3.00 (1) 2.86 (7) 3.00 (5) 2.91 (11) No. of groups heard only 2 2 0 1 2 2 6

*Infant + subadult

FIG. 2 Mean group size of eastern hoolock gibbons in stands of FIG. 3 Mean group size of eastern hoolock gibbons at various different numbers of trees in the study area, in the Lower Dibang distances from the nearest forest patch in the study area, in the  Valley district, Arunachal Pradesh, India (Fig. ). The numbers Lower Dibang Valley district, Arunachal Pradesh, India (Fig. ). above the columns are the total numbers of individuals counted.

predators of gibbons, particularly of immature animals. Myanmar border are physical barriers to the distribution Dogs are opportunistic predators, capturing gibbons when of the species. After the first distribution surveys of the east- they descend to the ground to move from one patch to ern hoolock gibbon in India (Das et al., ; Chetry et al., another in search of food and secure sleeping places. ) a population survey was carried out in Mehao Wildlife Sanctuary, in the Lower Dibang Valley district of Arunachal Pradesh (Chetry et al., ). Gibbon occurrence Discussion in the area is dependent on the presence of the local Adi and Idu-Mishmi tribes; the Adi hunt gibbons, whereas the Gibbons are known to occur in the tropical evergreen, trop- Idu-Mishmi do not. In this study we recorded gibbons in ical wet evergreen, tropical semi-evergreen, tropical moist isolated trees and small patches of forest surrounded by deciduous and subtropical hill forests of South-east Asia. agricultural land. The conversion of almost % of forest The geographical range of the eastern hoolock gibbon in to agricultural land in the study area has led to canopy dis- India is contiguous with its range in Myanmar through continuity, which prevents dispersal of the gibbons from the Chukan pass in Changlang district (Das et al., ). one patch to another unless they descend to the ground. It The Chindwin River and the mountains on the India– also makes them more easily sighted by hunters and

all seven study sites (i.e. breeding rates were similar) but the absence of juveniles indicates that their survival may be affected by fragmentation and lack of food. Female gibbons in forest fragments probably suffer high lactation costs because of an inadequate diet (Kakati et al., ), both in quality and quantity. In such a situation dependent infants are more likely to die when they stop suckling. When re- sources are scarce females may not survive to breed again (Moir, ). Chetry et al. () reported forest loss and fragmentation in Lower Dibang Valley district as a result of extensive agricultural practices (e.g. tea, ginger, corn and mustard cul- FIG. 4 The relationship between the encounter rate and the mean distance between groups of eastern hoolock gibbons in the tivation). We identified activities such as firewood collec- study area, in the Lower Dibang Valley district, Arunachal tion, selective tree felling, and encroachment for Pradesh, India (Fig. ). permanent settlement as indirect threats that may affect the gibbon population. Almost % of the total forest loss has occurred during the last  years, restricting the gibbons potential predators such as domestic dogs and predatory to small fragments of forest. Single-tree groups are most at birds such as the mountain hawk eagle Nisaetus nipalensis. risk as they are smaller than groups in forest patches. Fragmentation also causes deterioration of the habitat and Although hunting is not widespread in Idu-Mishmi tribal the elimination of suitable territories (Kakati et al., ) areas, even a low level of hunting can significantly affect and reduces the availability of suitable mates and the genetic the gibbon population (Fan & Jiang, ). Hunting pres- variability of the population (Jiang et al., ). The dis- sure has apparently led to the local extinction of the gibbon appearance of gibbons from small forest fragments has in the Adi-dominated area. In a tribal state such as been documented. Alfred & Sati () recorded the dis- Arunachal Pradesh, where hunting is part of the local cul- appearance of western hoolock gibbons from  forest ture, it is difficult to implement wildlife laws and protect patches (.–. km²) in jhum (slash-and-burn agriculture) species listed under the Indian Wildlife (Protection) Act, matrices in the Garo Hills of Meghalaya. This occurred . In addition to hunting and poaching, attacks by mainly because the jhum cycles (Kushwaha et al., ) domestic dogs are a threat (Panor, ). According to had shortened to ,  years and gibbon dispersal corridors local people, domestic dogs sometimes attack gibbons, par- (secondary forests and old-growth bamboo) were no longer ticularly immature animals that descend to the ground to available. move between forest patches. Little information is available on the populations of the Hoolock gibbons have been characterized as predomin- eastern hoolock gibbon in India. Other surveys have esti- antly frugivorous (Chivers, ; Tilson, ; Alfred & Sati, mated  groups ( individuals) in Namsai Forest ), with fruits constituting up to % of their diet Division,  groups ( individuals) in Koronu Circle,  (Chivers, ; Islam & Feeroz, ; Ahsan, ; Bartlett, groups (.  individuals) in Mehao Wildlife Sanctuary, in ). However, our study indicated a more folivorous diet Arunachal Pradesh, and  groups in Sadiya Forest Division, comprising % leaves and only % fruits and figs. Other in Assam (Das et al., ; Chetry et al., , ; Chetry studies have also recorded a significant reduction in the fruit & Chetry, ). Our study has added to the knowledge of content of the diet (Mukherjee, ; Kakati, ). the Indian population of the species and highlighted the Although it has been noted that folivory in hoolock gibbons conservation importance of the fragmented population in increases during the wet (monsoon) season, when fruit the non-protected forest areas of Arunachal Pradesh. tends to be less abundant (Gittins & Tilson, ; Alfred & The mean group size varies between habitats and de- Sati, ), our study was carried out in May, when fruits pends on the level of anthropogenic disturbance. The high- are normally more readily available than at other times. est mean group size for eastern hoolock gibbon (.) was A study of the species’ diet across seasons is needed to assess reported in the Namsai Forest Division, Lohit district annual dietary variation. (Das et al., ), followed by . and . in Lower Fan et al. () recommended long-term population Dibang Valley district in Arunachal Pradesh (Chetry et al., monitoring to determine whether hoolock gibbons can dis- , ). The smaller mean group size (.) in our study perse between fragmented forest patches. For effective con- area relative to other parts of the species’ range (e.g. . in servation management of gibbons and their habitat ongoing China; Brockelman et al., ; Fan et al., ) may be a evaluation of their status is necessary, particularly in areas result of forest fragmentation and human disturbance. We that hold a comparatively large proportion of the total found the ratio of infants to adult females to be similar in population in India (Struhsaker et al., ; Wilson &

 TABLE 3 Land use/land cover change matrix for the study area during –. The numbers indicate the change in area (km ); e.g. .   km forested land was converted to cultivated land, and a total of . km of forested land was converted to other land uses.

Sum of area (km2) 2010 1985 Cultivated land Water body Forested land Built-up area Total Cultivated land 137.20 2.25 28.90 1.41 169.76 Water body 8.18 25.33 6.07 0.00 39.59 Forested land 171.62 24.16 144.98 5.75 346.51 Built-up area 0.03 0.00 0.08 3.27 3.38 Total 317.04 51.74 180.02 10.42 559.23

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