The purpose of this project is to document the ecology of white-cheeked crested gibbons. Ecology, in its broadest definition, is how a species survives. A species’ ecology includes aspects of the environment it relies on to subsist, such as food, water, temperature, climate, habitat, and also how it relates to other organisms in the environment, such as prey, predators, and competitors. Surprisingly or not this species has never been studied before. In fact, most species of crested gibbons have not been studied in the wild. Crested gibbons are from the genus (next level up from species in taxonomy) Nomascus. There is a study in China of black-cheeked crested gibbons which has been ongoing for a few years but that is the only long term study of crested gibbons so far. Gibbons from the other genera (Hylobates, Symphalangus (commonly called siamang), and Hoolock) have been studied more in the wild. However, these gibbons are different from crested gibbons in several respects: body size, behavior (especially song), and ontogeny (development) primarily in terms of coat color changes. The habitat of crested gibbons is also unique. Most of their range is steep karst limestone mountains where the seasonal change and temperature variance is more extreme. I think the climate and environment is more unforgiving in general. Thus, we cannot extrapolate the ecology of crested gibbons from studies of other gibbons. Crested gibbons are critically endangered due to habitat destruction and hunting. Deforestation is ongoing here as development rapidly progresses. If we don’t know anything about a species’ ecology how can we hope to preserve it in the long term? That is why this ecological studied has been initiated.
The goals are:
1) Determine the ranging behavior of crested gibbons. Most importantly, how large are group territories? This is important because if we know how large territories are then we can use that to extrapolate out to how many gibbon groups could potentially live in an area. Ranging behavior is also linked to dietary strategies and seasonal change.
2) Determine the feeding behavior of crested gibbons. What do crested gibbons eat in the wild? Are they eating primarily leaves or fruit? If we know what they eat then it can aid us in determining what areas are suitable habitat for gibbons based on the presence of their food sources. We can also take better care of captive gibbons by giving them an appropriate diet. (They don’t eat bananas much in the wild but they love them at the zoo! Go figure..)
3) Describe the habitat of crested gibbons especially in terms of seasonal change affecting food trees. As I mentioned, range is often related to seasonality in food sources.
In order to determine diet and range we follow the gibbons and use GPS to record where they go. Over time we can use mapping software to calculate their home range. When they are seen feeding we record what they are eating and try to get plant samples so we can identify their food sources. For the habitat/seasonal data we have established transect lines through group territories. At each 10 meter point we mark all of the trees within a 5 meter radius. Every season we review all of the marked trees and record whether or not they are producing fruit, flowers, or leaves. Over the year we will end up with a picture of how the trees change.
Souliya measures the DBH (diameter at breast height) of a large mango tree
Somphet and Sangphet look for gibbons
Establishing a transect through dense growth
Estimate the height of this tree. It is not easy!
Sangphet marks the tree with a metal tag
One of the transects is right in our camp (notice the cooking pot!)
More soon!