The orangutan is an animal very close to my heart. I was lucky enough to work with some of these beautiful and engaging animals during a trip to Borneo a few years ago. There are only two species of orangutan left on the entire planet, both of which are endangered! One species is found on the island of Borneo and the other species on the island of Sumatra. The orangutan is an arboreal animal that lives in dense tropical rainforest. The recent destruction of its habitat for timber extraction and oil palm plantations has resulted in a considerable global effort to conserve the species, before it is too late. However, modern conservation projects are not just a simple case of instigating a rehabilitation, relocation or reproduction programme.
In-situ conservation requires an incredible amount of preliminary investigation and management once the programme begins. In particular orangutan population size and densities are not well known. Furthermore, the sample size used in many studies is often too small and does not give an accurate representation of the true orangutan population.
The most commonly used method of accessing population size is to take a nest census along a number of line transects. This method is slow and is limited to areas accessible by foot. A new method used for the first time in 2005, uses helicopters to take aerial surveys of population size. The use of a helicopter increases the size of the sampling area and can be completed much quicker than studies carried out by foot. As well as accessing population size, the genetics of the population must be considered. Genetic information is acquired from hair traps and faeces. Obtaining DNA in this way is non-invasive and the animal is completely undisturbed. This is good for an animal that when fully grown, can rip a human in half!
An area of Borneo that has been heavily researched by orangutan conservationists is Sabah, located in the north east of the island. Sabah is estimated to contain 11,000 orangutans at present (, a 35% decline in the population size 20 years ago). 6,600 individuals from the modern day Sabah population live in unprotected commercial forest reserves, subject to extensive timber extraction. There has been a considerable influx of individuals into these commercial areas, when their original habitats were converted to oil palm plantations.
Genetics studies have shown that the genetic diversity within the Sabah population is high. The genetics also showed that prior to the forest fragmentation, males frequently moved up and down the side of the river. By doing so they mated with different females and increased the gene flow between sub-populations. However, due to forest fragmentation, males are no longer able to do this and so gene flow is limited. If this is allowed to continue sub-populations will begin to become differentiated via random genetic drift. Another barrier to gene flow is the Kinabatangan River. Studies have shown that populations found at opposite sides of the river are not closely related and therefore the two populations do not interbreed.
Finally studies have looked at the reproductive activities of orangutans. It is essential to know social dynamics such as this before any relocation, or repopulation work can take place. It was originally thought (through observation) that female orangutans stay roughly in the area they were born and males disperse more broadly. However, genetics studies have shown there is no difference in the relatedness of both sexes for resident animals compared to the entire population. This suggests that both sexes disperse in a similar way. Early predictions suggest that both males and females stay close to where they are born and that these animals maintain loose social relationships together. It is unknown if this is the natural behavioural state of the animal or if it has been forced into this scenario due to the shrinking of suitable habitat.
The main recommendations that come from studies into the conservation of orangutans are to stop further declines in habitat availability and to join fragmented forest areas by planting forest corridors. The corridors allow orangutans to disperse and mate with individuals from other populations – therefore maintaining gene flow. However, it is incredibly difficult to acquire the land to create these corridors and even then it will take many years before the tree seedlings are capable of supporting a fully grown orangutan! There are also many other risk factors facing orangutan populations, such as hunting for bush meat and the illegal pet trade. It is clear further studies into the impact of logging and other human activities on orangutan ecology and survival are required. Furthermore currently active conservation projects must be managed to ensure they are effective and successful.