The Population of siamang ( Sympalangus syndactylus) in Damaran Baru Forest, Timang Gajah District, Bener Meriah Regency

The decline in the siamang population is due to increased trade, hunting and habitat degradation. The main buffer habitats generally only remain in forests with conservation forest status, one of which is the Damaran Baru Village Forest. This study aims to identify siamang populations in Damaran Baru Village Forest, Timang Gajah District. The research was conducted for one month from May to June 2023. The location was determined using a purposive sampling technique based on direct encounters and the tracks left by these animals. The research method used was observation with the concentration count, by recording the coordinates, height, number of individuals, sex of the animal and the number of each age class. The population was analyzed using the equation of population size and population density. Based on the data, the population was 15 individuals from 5 groups with a density of 6.97 individuals/km2. The age classes of adults (66.6%) and juvenile-1 (20%) dominated the age structure; hence, the population’s sustainability is considered good enough. Group 4 is the most balanced group in terms of age composition, because it has individual representatives in each age class. The sexual ratio in each group of siamang is 1:1.


Introduction
Siamang (Sympalangus syndactylus Raffles, 1821) is a species of primate whose habitat is spread across Malaysia and Indonesia (Sumatra).The existence of siamang plays an important role in the forest ecosystem, helping the growth process (forest succession or regeneration) by eating fruit and leaves.Like other primates, siamang also act as keystone species in ecosystems, helping to disperse plant seeds and acting as pollinators [1].The population of siamang is threatened due to reduce quantity and quality of habitat and hunting of wild animals.Siamang has category in endangered based on the IUCN (The International Union for Conservation of Nature) Red List (2019).Based on the level of threatened to the wildlife trade, siamang classified on Appendix I CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora), where their population are declining in natural habitat so their trade is very strict by the government.In Indonesia, siamang is protected by the state based on the Regulation of The Minister of Environmental and Forestry Number P.106 of 2018 [2].
Currently, the remaining siamang populations in Sumatra are mostly found in protected and conservation areas [2].Among of the Hylobatidae group, information on the siamang population is still included in the No Previous Population Estimate Available (NRA) category, which means there is no current information regarding the number of siamang populations.Information that is more than 20 years old is not considered relevant [3].Indications of a population that is having difficulty developing can also be seen from the small number of groups that have offspring.Siamang takes a long time to regenerate.Because siamang is a monogamous animal and individual siamang will be formed new group after passing through the almost adult phase when the siamang individuals are already present ready to reproduce.When the adult siamang individual has found it mating and then breeding, siamang take approx.seven months for the pregnancy period with a gap between the birth of one child and another the other is two to three years old and during its life the siamang can give birth up to four times with age up to 25 years [4].
Aceh is an area that has primary forests as siamang habitat.Studies on the siamang population in Aceh, especially in the Damaran Baru Village Forest, have never been carried out even though data population is needed in conservation activities.Research related to siamang in Aceh is still limited to the influence of forest structure on the density and habitat preferences of gibbons [5], protection of siamang food trees [6], as well as studies of daily behaviour of siamang in ex-situ [7].Therefore, it is hoped that this research can be an additional reference for siamang conservation efforts, especially in the Damaran Baru Village Forest.The aim of this research was to determine the siamang population based on group size, age structure, and sexual ratio in the Damaran Baru Village Forest.

Times and research location
The research was conducted from May to June 2023, in the Damaran Baru Village Forest, Timang Gajah District, Bener Meriah Regency (figure 1).The research location is geographically located at N 4° 45 ' 26.2965"East Longitude and E 96° 48' 34.5627"South Latitude, right below the Burni Telong Volcano with an altitude of 175 meters above sea level to 2450 meters above sea level.Damaran Baru Village Forest has a slope between 0 ->40%.The lowest temperature ranges between 18 o C and the highest temperature 24 o C with humidity ranging from 80 -90%.The size of the research location is 256.1 hectares, of which the land cover is community plantations 14%, Burni Telong Volcano 24.79%, protected forest 55.41%, and landslide-prone 5.51%.Siamang observations were carried out in nine tracks with cover types consisting of secondary forest, mixed plantations, and shrubs.

Research tools and objects
The tools that will be used in this research are 1) map location, 2) compass, 3) tally sheet is used for collecting information through siamang observation and counting, 4) Global Positioning System (GPS) map 78 SEA to record the coordinates when the siamang was found, 5) camera Nikon D5000 75-300 mm for siamang documentation, 6) binocular Bushnell 10-90X80 Zoom to enlarge images of siamang during observation.The research object observed was the siamang's population in the Damaran Baru Forest, Timang Gajah District, Bener Meriah Regency.

Data collection technique
The composition of the siamang population was obtained through observations using the concentration count method, observations were made centrally at points estimated to have the highest intensity of siamang encounters.Location coordinates and altitude are recorded if the presence of siamang is detected through direct encounters and traces left by siamang such as dung, food remains, and sounds.Before making observations, a two-week habituation process was carried out so that the siamangs got used to the presence of the observer.This aims to ensure that the siamangs are not too disturbed by the presence of observers when collecting data.
The observation track is aligned with the track created by the Lembaga Pengelolaan Hutan Kampung (LPHK) Damaran Baru Village Forest, Timang Gajah District, Bener Meriah.There are nine lines in the secondary forest, mixed plantations, and shrubs with a total transect area in the three land covers of 18.7 ha.The transect lengths are not the same because they follow topographic conditions, and the path width is 50 m each on the left and right of the path.The data recorded are the number of individuals, sex ratio, age structure and number of groups.Observations were made by recording the number of groups and the number of individuals on each route traversed.The number of individuals in a group is recorded to obtain a group size which is expressed as the number of all groups in a certain area and time.To avoid double counting, groups are determined based on distance, where 200 m is a safe distance to differentiate one group from another [8].Age structure is the age level in a group, namely infant, juvenile-1, juvenile-2, sub-adult, and adult.To obtain the age structure and sex ratio, this was done by recording the number of infant, juvenile-1, juvenile-2, sub-adult female or male, and adult female or male.Observations were made from 08.00 WIB when the siamangs were active until 18.00 WIB when the siamangs looked for places to sleep.

Data analysis
The observational data is presented in the form of tables and graphs, so that the composition of each group, group size, number of individuals, age structure and sex ratio can be seen.The encounter coordinates data were processed using Geographic Information System (GIS) to produce a map for the distribution of siamang and were interpreted descriptively.The description of the distribution map is associated with each habitat type in the location and its characteristics.Additionally, the data related to the siamang population were analysed to obtain information on population size, density, sex ratio, and age structure.
The calculation of the siamang population is carried out using the principle that when the population size in reproduction is smaller than the other members it is considered invisible so that the population size can be identified by the equation [9]: Where P is population size (individual) and nmax is the largest number of population sizes found (individuals).
Population density (D), according to [10], is the total population size divided by the total area used: The D is equal to population density (individuals/km 2 ), P is population size (individual), and A is area (km 2 ).Productivity can be obtained by dividing the number of offspring by the number of adult females multiplied by 100%.The increase in the siamang population was obtained by using a birth rate approach with the approach of the initial age of female siamang giving birth and the maximum age at which the female siamang can still give birth to offspring, and the time interval for giving birth to offspring (length of pregnancy, and breastfeeding and weaning period), as well as the age of the oldest siamang giving birth refers to [11], assuming there is no mortality rate and habitat disturbance The sex ratio (S) is the ratio between the number of males and females in a population of group: Where S means sex ratio, X is number of male individuals in a group of total, and Y is number female individuals in a group total.
The population age pyramid according to [12], can be obtained using the formula: According to [13] the age class of gibbons is divided into five classes infant, juvenile-1, juvenile-2, subadult, and adult.The difference between these age classes are: 1.The infant is the phase that begins after birth until the age of two or three years with a tiny body size.The young ones are usually carried by their female parent during the first year and their male parent during the second year.2. Juvenile-1 is the phase that starts from about two to four years with a small body.At this stage, they can move independently but still prefer to be close to their mother.3. Juvenile-2 is about four to six years old with medium body size.At this stage, they often move and look for their food.4. Sub-adult is the phase that begins from the age of six years.They have almost the same body size as an adult.However, they are often separated and not sexually mature.5. Adults are individuals with maximum body size, live in pairs, and are always close to their children.

Group size and population
The distribution of siamang groups in the Damaran Baru Village Forest is at an altitude of between 1538 and 1760 masl with a slope exceeding 40%.[14] stated that siamang is rarely found above an altitude of 1500 masl, although they can be found up to an altitude of 1828 masl.This difference could be caused by variations in the availability of siamang food trees at different heights in various locations.In line with [15] who said that the higher an area, the fewer types of vegetation there are, especially the types of trees where siamang move and look for food.Based on the nine tracks, only three tracks encountered siamang (figure 2).Siamang was not found on every tracks due to research conducted in May to June is the month of transition from the rainy season to the dry season.So temperatures still tend to be low with high humidity, and conditions where it still rains frequently.Minimum temperature in Damaran Baru Village Forest in May is 18 o C with maximum humidity reaching 90%.This has an impact on the activity of siamang where choose to take cover and rarely move when it rains.When it rains, gibbons prefer to take shelter in tree branches that are more than 30 meters high [16].When it rains in the morning, the sound of the siamang is usually not heard.Observations show that when the weather is cloudy, groups of gibbons tend to speed up their activities and move to safer parts of the forest, often not far from the trees where they sleep.This shows that siamangs have a fair amount of weather, and they take action to avoid bad weather.According to [17], environmental physical factors such as temperature, intensity light and humidity greatly influence what siamang do and when transition conditions from the rainy season to the dry season siamang don't do much activity.Other factors that influence the discovery of siamang is the availability of food and sleeping trees, the topographic conditions of the research area, and the ability of the observer.

Figure 2. The distribution of siamang's groups in Damaran Baru Village Forest
Table 1 show that the siamang population size in Damaran Baru Village Forest, numbering 15 individuals, was smaller than the siamang population size in Dolok Sipirok, North Sumatra, which reached 24 individuals [18], as well as in KHDTK Aek Nauli, Sumatra North which reached 23 individuals [15].However, the gibbon population size in the Damaran Baru Village Forest is larger than the siamang population found by [6] of 8 individuals in Rainforest Lodges Kedah, Gayo Lues Regency, Aceh.The low population of siamangs in the Damaran Baru Village Forest is thought to be caused by several factors, including the process of forming population groups and the availability of food.Population formation is influenced by the need for shelter, food and reproduction which is the same as the needs of primates for survival, as explained by [19].Apart from that, animal groups are also influenced by immigration, emigration, birth and death rates, as stated by [20].In addition, the size of the population can be influenced by the initial age at which sexual maturity is reached, in accordance with the theory put forward by [21].These factors can influence the dynamics of siamang populations in various locations, resulting in differences in population numbers between one research area and another.Group size refers to the number of individuals in a group, while population size refers to the total number of individuals in an area at a certain time [22].Based on the observation in the nine tracks, five groups of siamang were found, four groups were in secondary forests and one group was in a mixed plantation area.Siamangs are more commonly found in secondary forests, this is thought to be because the secondary forest land cover type has tall and strong trees that allow siamangs to move freely [23].In the secondary forest in the Damaran Baru Village Forest offers more diverse food sources and a more stable habitat.The number of individuals in the siamang population was recorded as 15 individuals.In detail, around 13.33% of the siamang population has the smallest group size, namely only 2 individuals per group, 60% is in a group of 3 individuals, and 26.66% is in a group of 4 individuals (figure 3).[24] noted that the size of a siamang group is influenced by some factors, including the environment in which they live which influences the process of raising young and the availability of food sources.This supports animal population growth and healthy regeneration.Several types of trees that siamang use as a food source include biwa (Eriobotrya japonica), melinjo (Gnetum gnemon), cempaka hutan (Manglietia glauca), rembele (Saurania sp.), geseng (Lithocarpus sp.), and gondang (Ficus variegata Blume).Food availability is a key factor in maintaining the survival of wildlife, and climate change can affect food availability.If the habitat no longer meets the animals' needs, they will look for alternative food sources and habitats [23].The number and size of siamang groups found in the Damaran Baru Village Forest in this study was lower than the findings reported by [8] in the Batang Toru Ecosystem, South Tapanuli Regency, North Sumatra Province.[8] found 15 siamang groups with group members ranging from one to five siamang individuals per group.This difference can be caused by differences in the size of the observation area, with the area in Batang Toru being larger, reaching 1.251 ha, as well as lower altitudes, ranging from 800 to 1200 masl.However, when compared with research in the Guguk Indigenous Forest, Merangin Regency, Jambi Province, conducted by [24], the number and size of siamng groups in the Damaran Baru Village Forest is still higher.Research by [24] found only two groups with group sizes of two to three siamang individuals.The small group size found in this study was caused by the process of forming a new group in one of the groups, which consisted of one male siamang individual and one female siamang individual.This process is in line with the findings of [25], who stated that these new groups had small group sizes because they did not have many children.The social system of siamang has unique characteristics, where they form small families as a core group.Siamang live in pairs with up to four cubs, and when the cubs grow up, they leave the group because older group members are often aggressive towards young of the same sex [20].In group travel, the female often takes the lead and sometimes waits for a while and returns if the other members do not follow [26].The number and size of the siamang group in the Damaran Baru Village Forest is also higher compared to the results of research in the Register 25 Pematang Tanggang Protected Forest, Tanggamus Regency conducted by [27].In his research, siamang group sizes ranged from 2-3 individuals.This may be due to overlapping hunting areas in the registered protected forest as well as the combined vocalizations of several primates that are close together, making it difficult to identify groups.Apart from that, [28] in the conservation forest of PT.Tidar Kerinci Agung, South Solok, West Sumatra, shows that there are six groups of siamangs with group sizes ranging from two to four individual siamang.

Land of covers
Population density is an important indicator in assessing the abundance of a species in an area.The ideal siamang population density cannot be determined with certainty, because there is no data on siamang population density in Damaran Baru Village Forest that can be used as a reference.In the Damaran Baru Village Forest, the siamang group has a density of 2.3 groups per square kilometer and 6.97 individuals per square kilometer.The density of this group of siamangs is lower than previous research conducted in Kerinci Seblat National Park, Pesisir Selatan Regency, by [29] who recorded a siamang group density of 2.45 groups per square kilometer.Likewise, in the Batang Toru Forest Area studied by [25] the population density reached 3.37 groups per square kilometer and 9.37 individuals per square kilometer.Population density can be influenced by a number of factors, including vegetation structure and composition, food availability, and demographic factors [30].Observations show that siamangs use mixed plantations as a foraging area and as a movement route to secondary forest.Group 4, for example, only explored the mixed plantations looking for food and did not stay there at night.This is related to the limited number of trees that can be used as sleeping trees in mixed plantations.[31] noted that primates often choose trees with dense and strong canopies as sleeping trees at night.Apart from that, considerations of predator safety, comfort, and energy use in searching for food are also factors that might explain why siamang groups do not use mixed plantations as their habitat.
Siamang predators identified in the Damaran Baru Village Forest include the sumatran clouded leopard (Neofelis diardi), black eagle (Ictinaetus malaiensis), and sun bear (Helarctos malayanus).Although researchers only found black eagles (Ictinaetus malaiensis) during the research, the presence of signs such as droppings thought to be from Sumatran clouded leopards (Neofelis diardi) and claw marks from sun bears (Helarctos malayanus) (Figure 4) indicate the presence of this predator.These predators play an important role in forest ecosystems and can affect the health of the ecosystem as a whole.They also play a role in controlling animal populations on the seabed, including siamangs.The presence of these predators plays an important role in maintaining ecosystem balance.If the top predator of this ecosystem disappears, a trophic cascade phenomenon can occur, where changes in the predator population can affect the structure and dynamics of the ecosystem as a whole [15].

Age Structure
Age is an important parameter that can be used in managing wild animal populations.Understanding age structure is crucial in initiating the regeneration of wild animals.In forest environments with dense upper canopy strata, determining the sex of primate individuals that have not yet achieved perfect sexual characteristics can be a difficult task [24].According to [32], identifying the sex of primate individuals who are still cubs or juveniles with incomplete sexual characteristics is also difficult to detect.Figure 5 show that the age classes of adult siamang dominate the population.It can be seen that the proportion of age structure of all siamangs in the Damaran Baru Village Forest is five pairs of adult males and adult females (66%), three juveniles-2 (20%), one juvenile-1 (6.7%), and one infant (6.7%).The result indicate that the siamang population in Damaran Baru Village Forest is possible to develop over several years early, but it will difficult to develop on the following years, due to the lack of number of groups of juvenile and infants.

Figure 5.
Siamang's age structure in Damaran Baru Village Forest.[33] explain that the population will stabilize when the number of individual ages youth is higher than the number of individuals of productive and unproductive age.Infant individuals are particularly vulnerable its existence in a group, because individuals are individual up to two years old year old still in its mother's arms.Survival infant individuals in monogamous animals require more care if compared to non-monogamous animals [34].Siamang takes a long time to regenerate.This can be seen from the relationship between the low number of siamang individuals in infant and adult age classes according to annual intervals (table 2).The presence of a small number of groups that have offspring can be an indicator of a population that is difficult to reproduce.For example, during observations three juvenile-2 siamangs were identified who would soon enter the adult phase and form a new group to then breed.Because siamang is a monogamous animal and individual siamang will be formed new group after passing through the almost adult phase when the siamang individuals are already present ready to reproduce.When the adult siamang individual has found it mating and then breeding, siamang take approx.seven months for the pregnancy period with a gap between the birth of one child and another the other is two to three years old and during its life the siamang can give birth up to four times with age up to 25 years.This is possible in the age class of male and female adults have a very grade of 66.6 % (Figure 5).A group of siamang was identified that had a similar age structure complete in it, namely group 3, where in each his age class was represented by one individual, except for the juvenile-1 age class (table 1).The phenomenon of groups with numbers more than four individuals due to the presence of adult offspring that have not yet been established pairs [25].This means that it is at the secondary forest has a suitable habitat for the survival of siamangs because it can provide sufficient food sources for a group of siamangs with maximum amount.Figure 5 show that groups 1, 3, and 4 there are juvenile and infant siamang, which are a potential age phase.This indicates that the siamang population in the Damaran Baru Village Forest has the potential for good growth and development in the future.The situation is different from group 2, where no juveniles or young were found.This allegedly happened because in this group, adult male and adult female individuals had just joined to form a group, so they did not yet have children.Other factors that influence this situation include the availability of food sources [31], protection of group members [35], and the energy required by group members when foraging [36].In mixed plantation habitats, vegetation is sparser than in secondary forest, so there are fewer food sources, sleeping trees, and shelter for siamang from predators.
Based on the age structure of the siamang group in the Damaran Baru Village Forest that present in table 2, shows the ratio of adults, juvenile-1, and infant age for that matter respective regions are 10:3:1.But table 2 also shows the condition of the different age structures.After dividing age range, juvenile-1is the widest compared to other classes.It can be concluded that the siamang population in that location has a balanced age structure, and is possible to develop in the next few years.This approach is in line with the views of [36] who explains that in population conditions that growing rapidly, dominated by young individuals.In the secondary forest location, the situation was also favourable for one individual infant and one individual child from two different groups, which indicates that the development of the siamang group can proceed well in this location, supported by the availability of food sources that suit the siamang preferences.As stated by [20], the population of siamang populations over time is very dependent on environmental conditions.

Sexual ratio
Sexual ratio plays an important role in the development of siamang populations and can influence population stability.Sexual ratio refers to the ratio between male and female individuals in a population.Based on the results of sex identification in the adult siamang category, a male to female ratio was obtained of 1:1 (adult male: adult female) (Tabel 2).With this balanced sex ratio, the siamang population in the Damaran Baru Village Forest still has the potential to reproduce, because the population of male and female siamang is balanced.This condition is in accordance with the monogamous nature of siamang, where male and female pairs are monogamous, and a sex ratio of 1:1 is required to maintain population stability [37].
This research does not mention the sexual ratio for the adolescent and child siamang age groups, because their sexual characteristics have not yet developed fully and have not yet reached reproductive age.This is in line with [32], who stated that determining the sex of individual juvenile primates and children with sexual characteristics that have not yet developed or do not show clear signs will be difficult.Through a comparison of the sexual ratios found, it can be concluded that siamang reproduction has good potential in the future.Reproductive success is highly dependent on the age of sexual maturity, with siamang reaching first sexual maturity at the age of 7-8 years for both males and females [38].In the wild, siamang pairs usually live to be around 25 years old.The productive age is quite early, each female has the potential to give birth to 2-3 children during her lifetime [26].With five productive female individuals in the siamang population in the Damaran Baru Village Forest, it can be estimated that during her lifetime, each female will contribute to population growth of 10-15 new individuals.

Conclusions
The siamang population in the Damaran Baru Village Forest is 15 individuals with an age structure of 66% adults, 20% juveniles-2, 6.7% juveniles-1, and 6.7% infant.Each group consists of up to four individuals.The sexual ratio in each group of siamang is 1:1.

Figure 1 .
Figure 1.Map of research locations in Damaran Baru Village Forest.

Figure 3 .
Figure 3.The average population size of each groups.

Table 2 .
Age structure of siamang population in Damaran Baru Village Forest.