, the animals of Borneo being consistently darker in color than those on Sumatra" (Grzimek, 1990, p. 402). The difference in coloration can probably be explained by the two different locales found in the forests of Borneo and Sumatra. As for the infants being bright orange, perhaps this is an identifying marking so that parents do not lose sight of their vulnerable offspring. At the same time however, the bright orange coloration would seem to make them more susceptible to predators.
McKinnon found that although orangutans live primarily in the trees, they still have ground-dwelling predators. The orangutan's chief enemies include the lurking tiger and the red dogs (to be found on Sumatra but not on Borneo). McKinnon reported that "clouded leopards are agile climbers, and pursue young orangutans. Large pythons may also catch young orangutans if they venture out on the forest floor, where they are also liable to attack by blood-sucking leeches" (Grzimek, 1990, p. 404).
Like all apes, orangutans are adept at using tools, and their use of sticks to gain access to honey in the recesses of trees is well documented. Tool use among orangutans is significant because past researchers had believed that the ability to make and use tools was something that only emerged in our chimp-like ancestors.
Carel Van Schaik, a primatologist at Duke University, conducted research on the orangutan in its
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