This trait is also observed in the hands of orangutans, spider monkeys, and, of course, other gibbons.
Centre ValBio at Stony Brook University
Not only does the siamang's expertise in the trees give them access to more food, but it also takes much less energy to swing from branch to branch than it does to walk on the ground. Siamangs have dark black fur with gray or reddish hairs scattered around their mostly naked face.
Their fur is relatively shaggy compared to other gibbons. Brachiation: Also called arm swinging, is a form of arboreal locomotion in which primates swing from tree limb to tree limb using only their arms. Diurnal: Active during daylight hours. Indigenous: Originating or occurring naturally in a particular place; native. Monogamous: Having only one sexual partner. Siamangs eat from over different types of plants, usually changing their diet depending on the time of year.
Original Research ARTICLE
They prefer young leaves to mature leaves and, in many cases, avoid mature leaves altogether. The rest of their day is spent traveling from one food patch to another and grooming each other. There are no major behavioral differences between the two subspecies, although the Sumatran siamang spends less time foraging, thanks to its nutrient-rich, fruit-heavy diet. The family is made up of a monogamous mating pair of adult siamangs and their offspring who have yet to leave the family.
Families are fiercely territorial and rarely venture out of their range. Thanks to their size, agility, and safe location in the trees, siamangs have no known natural predator. Communication Calls from siamangs most often serenade their forests in the mid-morning period between 9 and 10 a. Calls are generally used to establish territory, but mating pairs may also sing together to strengthen their bond.
Siamang calls are louder than most gibbons, traveling upwards of over 1. A typical siamang song has two parts. First, the siamang sings into the gular sac, causing it to expand and let out a low moaning sound almost like a "bloop" that can resonate through thick forests. Then the siamang opens his mouth to make several loud, high-pitched cries in quick succession. This will go on for 10 to 20 minutes. The mother is pregnant for a period of 7 to 8 months.
Once born, the baby siamang will cling to his mother for around 8 months. After that, the father takes on a more prominent role by holding onto the baby until he gains enough independence to travel on his own, usually at age 3. The siamang then enters the subadult phase, where he will stay with his family until he has fully matured into an adult between his 6th and 8th year, at which point the siamang will leave to find a mate and start a new family in a new territory although there may always be a power struggle for their current territory.
When food availability is at a constant, such as in a zoo, siamangs will mate year-round. When they eat the fruit of one tree, they defecate its seeds anywhere throughout their territory, leading to a healthier, more diverse tree population. Their two biggest threats are habitat loss and illegal pet trade. In addition to road building and illegal logging, the single biggest reason for habitat loss is the palm oil industry. In addition, due their behavioral flexibility, chimpanzees might be able to adapt to savanna and anthropogenic habitat mosaics and persist there long-term, though likely at lower densities Hockings et al.
For example, it has been shown that although chimpanzees at Fongoli, Senegal, a site with strong seasonality in temperature and rainfall, experience heat and dehydration stress, chimpanzees likely developed mechanisms for avoiding costs of energetic constraint Wessling et al. However, these types of landscapes are still less surveyed, and longitudinal data from more sites are needed to determine the population trend, especially from Guinea-Bissau, Mali, Senegal, and Sierra Leone for which such data are lacking.
Consequently, this study can only be regarded as a first step and follow-up studies are needed to substantiate our findings. Our study revealed three factors having a positive effect on chimpanzee densities; habitat protection, reduced accessibility, and hunting taboos. The first two factors are already reflected in commonly implemented conservation interventions, such as protected areas, law enforcement, and the presence of researchers, NGOs and tourism activities, which have also been shown to have a positive effect on ape persistence Campbell et al.
The mechanism underlying those activities is threat exclusion, meaning threats are excluded from delineated areas. In contrast, the positive effect of hunting taboos is based on a different mechanism, namely the reduction of a threat, in this case due to a particular human behavior. While threat exclusion addresses the symptoms of conservation challenges, threat reduction aims to focus on the root causes.
Previous studies argued that for conservation to be successful, threats need to be actively reduced Allison et al.
However, in a recent compilation of available evidence for the effectiveness of conservation interventions for primates, the majority of interventions was aimed at threat exclusion, for example through protected areas, law enforcement, and species management Junker et al. There is considerably less evidence for interventions targeting threat reduction Junker et al.
While the positive effect of hunting taboos we found for chimpanzees cannot be directly transferred to other areas, conservation interventions mimicking these conditions could complement current conservation efforts. The positive effect of hunting taboos is a challenge for conservationists, because they generally have a religious or a supernatural basis, both in their origin and in their maintenance Colding and Folke, While taboos can be strengthened or reinforced where they already exist Junker et al. An additional concern is the loss of power of traditional taboos through modernization and migration, with people from different cultural or religious background being less likely to accept local taboos Golden and Comaroff, Mimicking hunting taboos would mean to reduce the demand for chimpanzees by consumers and discourage the supply by hunters and traders.
From a consumer perspective, chimpanzees are not a notable protein source, and the provision of alternative protein sources is a common intervention aimed at reducing the economic incentive to consume bushmeat, including chimpanzee. Junker et al. Another important conservation intervention includes awareness raising activities, especially because in certain areas medicinal or magical properties are assigned to chimpanzee parts and chimpanzee bone powder Hanson-Alp et al. There are studies that have shown a positive effect of such interventions on bushmeat consumption, for example in the context of repeated multimedia campaigns Kouassi et al.
However, hunting chimpanzees is also strongly driven by a demand for chimpanzee parts and live animals from urban areas and even international markets Kuehl et al. Awareness raising activities at national or even regional scale specifically targeting urban consumers is absent from West Africa, but could be an important tool to reduce the acceptability of chimpanzee consumption. Evidence from China suggests that an ambitious nation-wide awareness raising campaign championed by the most popular Chinese athlete, Yao Ming, resulted in a change in government policy and a strong decrease in shark fin demand across China Whitcraft et al.
In general, research on behavioral change in conservation highlights the need to go beyond awareness raising because often a change in awareness alone is not enough to lead to pro-environmental behavior Schultz, ; Amel et al. Stakeholder co-designed behavioral change tools therefore try to identify barriers to behavioral change as well as providing benefits Schultz, Successful examples of behavioral change interventions aimed at reducing bushmeat consumption include the so-called community-based social marketing tool, that has been implemented to reduce consumer demand for wild meat in a Brazilian town, and that explicitly identified and then reduced barriers to the consumption of domesticated meat Chaves et al.
From a supplier perspective, chimpanzees are mostly killed or captured opportunistically, but because of their large size, hunters make high profits from a single catch, and young chimpanzees can be sold for the pet trade Hanson-Alp et al. Even such single catches can have detrimental effects on chimpanzee populations due to their long time to maturation and long inter-birth intervals. As discussed above, law enforcement aiming to exclude hunters from certain areas often seems not to be sufficient, mainly due to the virtual impossibility of stopping every single hunter.
Conservation interventions aiming at reducing chimpanzee supply are scarce, and here again stakeholder co-designed behavioral change tools might be a way forward to first understand what is driving certain behaviors and how hunters could be motivated to not kill or capture chimpanzees despite their high monetary value. While there is evidence that monetary and non-monetary benefits can have a positive effect on primate populations, there are also studies showing no effect Junker et al.
In addition, studies looking at the entire supply chain from individual hunters via traders to sellers have identified multiple entry points for conservation interventions Bachmann et al. The positive deviance approach can be a useful tool for conservation science because it focuses on identifying conditions or mechanisms that have already proven to work.
While understanding threats to species is a prerequisite for conservation planning, solutions are often a lot less understood. The positive deviance approach allows directing research toward possible answers to conservation challenges. In general, this approach can be applied to any taxon, region and at different spatial scales, if matched with data of corresponding resolution and quality.
Importantly, the spatial scale needs to be chosen so that there is sufficient variation along multiple predictor variables. Similarly to Frei et al. First, it is difficult to differentiate between the influence of historic and current conditions, i. This is of particular concern for species with slow life histories. Second, the data, especially when it pertains to human behavior or socio-economic context, might not be available at a small resolution for a large area, which makes large-scale analyses difficult.
High Altitude Primates
Here, multi-scale studies might give additional insights. In general, many more studies using the positive deviance approach would be needed to determine whether this is truly a useful approach that can provide novel insights for species conservation. Conservation interventions, especially for the conservation of primates, still largely focus on habitat protection and reducing accessibility for humans through protected areas and law enforcement.
By using the positive deviance approach, we found high chimpanzee densities and seemingly stable population trends for sites with a high prevalence of hunting taboos, even though those areas were not set aside under any high-level protective status. This suggests that these enabling conditions can be mimicked by using stakeholder co-designed behavioral change approaches Schultz, , ; Chaves et al. While new behavioral change tools have been applied to different environmental problems, they remain largely absent from primate conservation Junker et al.
With a lot of organizations already working for the protection of chimpanzees across West Africa and the relatively strong support that chimpanzee protection garners within and outside its range, this might be an opportunity to pioneer and test new conservation approaches, which, if successful, could inform protection of other primates. Applications of the positive deviance approach to species conservation are still rare, and many more studies and methodological advancements would be needed to establish this method as a useful conservation science tool.
All authors contributed to the reviewing and editing of the manuscript, and approved its submission. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We would like to thank all governments and national authorities in the chimpanzee range countries in West Africa for providing permission for data collection.
We further thank Thomas Esch for providing Global Urban Footprint data for West Africa, Julia Riedel for help with data curation and Mona Bachmann for insightful discussions on drivers of bushmeat hunting. We thank Marc Ancrenaz and Alex Piel for their helpful comments on the manuscript. Adanu, J. Sommer and C. Alkire, S.
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