National Geographic : 1998 Aug
Boom or Bust The research site in Gunung Palung National Par covers eight square miles of rain forest, and a gric (dashed lines) permits quick access to the varied I occupied by orangutans. My dedicated team of Ir and Western assistants and I have logged more th hours observing the apes. Their movements are h influenced by the presence of ripe fruit. Depicted map are the paths of five orangutans observed du sample periods, with dots marking the places wh< slept at night. During the mast fruiting, oranguta found mostly in the alluvial terraces and lowland where dipterocarp seeds, durians, and other fruit, abundant. During fruit-poor periods the apes oft ranged more widely between habitats while searc] food. Recording such travel helps us develop a cle picture of the complicated orangutan social syste the way each animal's home range relates to other approach has, for example, led to the finding that many as six adult males may range independently a given area at the same time-a surprising degre territory overlap. Peat swamp In flat, poorly drained areas with sai soil, organic material builds up on ti forest floor, and tannins tint the wat This forest is host to important oran fruit trees, such as Palaquium leioci (foreground) with its stiltlike roots. High-fruit period: An orangutan's diet during a mast fruiting is higher in calories than at other times. My research has shown that this is due to a higher carbohydrate and lower fiber content. Alluvial terrace forest Rich soils support large dipterocarps and the highest density of vines and strangler fig trees, as well as a lush herbaceous layer at ground level. This constitutes the richest habitat for orangutans within the research site, especially duringthe mast. Low-fruit period y avail able, orangut relatively plentiful foods, such as laes, figs, ginger stems, and the inner layer of bark. Low-fruit periods can last for months.