Sumatran orangutans are primarily frugivores, favoring fruits consisting of a large seed and surrounded by a fleshy substance, such as fig fruits. Insects are also a huge part of the orangutan’s diet; the most consumed types are ants, predominantly of the genus Camponotus (at least four species indet.). Their main diet can be broken up into five categories: fruits, insects, leaf material, bark and other miscellaneous food items. Studies have shown that orangutans in
the Ketambe area in Indonesia ate over 92 different kinds of fruit, 13 different kinds of leaves, 22 sorts of other vegetable material such as top-sprouts, and pseudo-bulbs of orchids. Insects included in the diet are numbered at least 17 different types. Occasionally soil from termite mounds were ingested in small quantities. When there is low ripe fruit availability, Sumatran orangutans will eat the meat of the slow loris, a nocturnal primate. Water consumption for the orangutans was ingested from natural bowls created in the trees they lived around. They even drank water from the hair on their arms when rainfall was heavy. Meat-eating happens rarely in Sumatran orangutan, and orangutans do not show a male bias in meat-eating. A research in Ketambe area reported cases of meat-eating in wild Sumatran orangutans, of which 9 cases of orangutans eating slow lorises. The research shows, in the recent 3 cases of slow lorises eaten by Sumatran orangutan, a maximum mean feeding rate of the adult orangutan for an entire adult male slow loris is 160.9 g/h and, of the infant, 142.4 g/h. No case have been reported during mast years, which suggests orangutans take meat as a fallback for the seasonal shortage of fruits; preying on slow loris occurs more often in periods of low fruit availability. Similar to most primate species, orangutans appear to only share meat between mother and infants.
After an hour of observing those orangutans and finishing their eating, the team started leaving forest. The Indonesian guides collected all left over and skins of fruits, as human beings are not allowed to feed wild lives or leaving anything behind which could be consumed by them.
Sumatrans encounter threats such as logging (both legal and illegal), wholesale conversion of forest to agricultural land and oil palm plantations, and fragmentation by roads. Oil companies use a method of deforestation to utilize palm oil. This palm oil
is taken from the trees in which Sumatran orangutans live and swing from. An assessment of forest loss in the 1990s concluded that forests supporting at least 1,000 orangutans were lost each year within the Leuser Ecosystem alone. While poaching generally is not a huge problem for the Sumatrans, occasional local hunting does decrease the population size. They have been hunted in the Northern Sumatra in the past as targets for food; although deliberate attempts to hunt the Sumatrans are rare nowadays, locals such as the Batak people are known to eat almost all vertebrates in their area. Additionally, the Sumatrans are treated as pests by Sumatran farmers, becoming targets of elimination if they are seen damaging or stealing crops. For commercial aspects, hunts for both dead and alive specimens have also been recorded as an effect of the demand by European and North American zoos and institutions throughout the 20th century.
After witnessing this amazing last few creatures of Sumatra, we started towards camping ground at nearby village where we would take rest in the evening and plan for next day morning.
During this trekking we also spotted lot of Indonesian black squirrels and long tailed macaque in forest as well as in village. The time of the day, climate and nature of forest was not soothing enough for spotting birds as birds are really tiny in this forest and get completely camouflaged in thick leaves and high canopy. However, we spotted a pair of famous rhinoceros hornbill on a tree top. The rhinoceros hornbill (Buceros rhinoceros) is one of the largest hornbills, adults being approximately the size of a swan, 91–122 cm (36–48 in) long and weighing 2–3 kg (4.4–6.6 lb). In captivity it can live for up to 90 years. It is found in lowland and montane, tropical and subtropical climates and in mountain rain forests up to 1,400 metres altitude in Borneo, Sumatra, Java, the Malay Peninsula, Singapore, and southern Thailand. Like most other hornbills, the male has orange or red irises, and the female has whitish irises. This bird has a mainly white beak and casque, but there are orange places here and there. The tip of the casque curves markedly upward. The bird has white underparts, especially to the tail. The rhinoceros hornbill faces a number of threats, including loss of habitat and hunting for its meat, its feathers and its casque, which can be carved into ornaments and jewellery, and is as dense as ivory. IUCN status is near threatened.