How canopy structure affects orangutan nesting sites.

Undisturbed, primary forests are becoming increasingly rare due to forest fragmentation caused by human expansion. This poses a major threat to numerous endangered species that live in these forested landscapes.

A new study published in Biological Conservation centers around the fragmented forest region of Sabah, Malaysia, examining how fragmented forests affect the wildlife within. The region of Sabah, Malaysia exists within a collection of palm oil plantations and human settlements, and according to the authors the area had been heavily logged over the past century until protective forestry sanctions were enacted in 2005. The degradation of the forest though is extremely apparent. The area suffers from a low tree density of about 332 stems per hectare. Additionally, the existing forest exhibits a short canopy where more than 80% of the trees are less than 20 meters in height. There are also large canopy gaps and a significant amount of soil disturbance. Despite these seemingly large degradation factors, the region supports a significant Orangutan population, estimated to be at about 800 individuals in 2015. This is the result of a significant decline from an estimated 1,100 individuals in the early 2,000s.

The Bornean Orangutans of this region have somewhat adapted to living in these fragmented areas, but their changing environment may be taking a toll on their long term survivability. More than 70% of Bornean orangutans survive in degraded forests in Southeast Asia, but it is thought that in order for the species to survive long term, there may be a minimum ecological requirement that must be met despite their seemingly diverse adaptability. Using ground and air surveys of Bornean orangutan nest sites and airborne light detection and ranging (LiDAR) to examine the forest canopy structure, researchers found links between the location of Bornean orangutan nests and the structure of the forest canopy.


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Orangutan nests are an essential component of their ecology. It has been found that orangutans spend about 13 hours a day in their nests (more than half of their entire life!). So the factors affecting this component are extremely important to their survival.

Overall, Bornean orangutan nest sites were found to be positively correlated with taller trees and a more uniform canopy structure. This suggests to researchers that these nesting sites might offer an increased vantage point to an orangutan’s surroundings, allowing them to keep an eye out for predators or rival orangutans. Researchers think that this might also suggest a more stable sleeping environment since these trees tend to have thicker, more stable branches. Researchers also found that nesting sites were more common in non-fruiting trees, presumably due to the lower possibility of night foragers and predators that could cause a disturbance to the sleeping orangutans.

This study concludes that the overall canopy structure and composition heavily affects orangutan survival in any given forest. This provides a baseline of information on the minimum ecological requirements of orangutans in this region and could mean the difference between conservation and extinction.

Citation:

Davies, A., Oram, F., Ancrenaz, M., & Asner, G. (2019). Combining behavioural and LiDAR data to reveal relationships between canopy structure and orangutan nest site selection in disturbed forests. Biological Conservation, 232, 97-107.

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