The near-vegan lifestyle of wild orangutans in Borneo’s forests means the apes face recurring protein droughts severe enough that their body tissues start to waste away.
“They’re living on the margin,” says biological anthropologist Nathaniel Dominy of Dartmouth College.
Borneo, one of only two natural habitats for wild orangutans, is predominantly forested with trees that produce abundant fruit only about every five years. In bad years, the animals make do with a smaller volume of leaves and bark. During tough times, the apes average only about 1.4 grams of protein per kilogram of body mass per day, a tenth of what mountain gorillas consume, Dominy and his colleagues report online December 14 in Biology Letters. Such drastic protein shortage “emphasizes the critical need for forest preservation, including areas not usually considered prime orangutan habitat,” says evolutionary biologist Rob Shumaker of the Indianapolis Zoo.
Dominy and his colleagues pieced together the rare picture of protein budgets of wild orangutans by applying modern analytic techniques to urine samples collected from Borneo apes between 1994 and 1999.
Seeing these protein budgets is important for understanding how orangutans have adapted to survive in places with resources that fluctuate so extremely, says Mark E. Harrison of the University of Leicester in England, who also has studied orangutan feeding ecology.