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Feeding and Ranging Behaviors of Proboscis Monkey Nasalis larvatus in Sabah, Malaysia

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Title: Feeding and Ranging Behaviors of Proboscis Monkey Nasalis larvatus in Sabah, Malaysia
Other Titles: マレーシア・サバ州におけるテングザルの採食行動と遊動
Authors: Matsuda, Ikki1 Browse this author
Authors(alt): 松田, 一希1
Issue Date: 25-Mar-2008
Abstract: A one-male group (BE-Group) of proboscis monkey Nasalis larvatus consisting of the α-male Bejita, six adult females and some immatures was chosen and focal male and females in BE-Group were followed for a total of 1,968 and 1,539 hours, respectively, along the Menanggul River (which is a tributary of the Kinabatangan River), Sabah, Malaysia, focusing on feeding and ranging behaviors from May 2005 to May 2006. In order to determine the availability and seasonal changes of plant species consumed by the focal monkeys, vegetation surveys were carried out in 2.15 ha along 16 200-500 m trails set up in the forest. In addition, sleeping sites of all the groups in the area were surveyed in the evenings of 6-22 days per month using a boat along the river side. The main results were: 1) Sleeping sites of BE-Group were distributed in a wide range of overlap with those of other groups, suggesting no territoriality between different groups on the riverside trees. BE-Group seemed to select their sleeping sites on riverside trees at narrow river locations to reduce the predation chance of clouded leopard and/or to raise the probability of successful river crossing by females (often with infants) and juveniles to escape from predators. 2) As there was no difference in time budget between individuals excluding the category others (grooming + copulation) which contributed very little, the data of all focal monkeys were pooled, and its resting, feeding, moving and others accounted for 76.4%, 19.5%, 3.5% and 0.5%, respectively. In the feeding time, young leaves, fruits, flowers, mature leaves and other food sources constituted 65.9%, 25.9%, 7.7%, 0.03% and 0.5%, respectively, indicating that the tendency of consuming young leaves was strong in terms of total food amount. However, monthly fruit production of plants positively correlated with monthly fruit-eating and feeding activity of proboscis monkeys, respectively, though young leaf production to young leaf-eating and flower production to flower-eating did not correlate with each other, respectively, and both young leaf and flower production did not correlate with feeding activity. These suggest that fruit production significantly affects the activity budget of proboscis monkeys. 3) In both the male and females, the ratio of feeding time was the highest at 15:00 - 17:00, i. e. shortly before sleeping. As proboscis monkeys require about 50 hours for processing leaves, they may feed on lots of foods in late afternoon to spend the night time not only for sleeping but also for digestion. 4) Total number of plant species consumed by focal monkeys was 188 (127 genera, 55 families). When the availability of each species was estimated from the vegetation survey in which 180 tree and vine species were described and monthly followed their phenology, the actual observed time for consuming them was significantly different from consumption time expected from availability in some species, suggesting that the proboscis monkey is the picky eater. For instance, Mallotus muticus, Ficus binnendijikii, Crudia reticulate, Lophopyxis maingayi and so on were positively preferred by proboscis monkeys. 5) The seven focal monkeys spent a total of 177.2 hours for fruit-eating, of which seed-eating constituted 97%, suggesting that the proboscis monkeys seemed to consume the fruits in favor of seeds. Whenever monkeys collected ripe fruits, they abandoned flesh and consumed only seeds. They fed extensively on the seeds of Mallotus muticus trees and Lophopyxis maingayi vines which were the most abundant plant species in the study area, although some dominant and predominant species were not consumed or showed negative food preference. Because the proboscis monkeys almost completely grind and digest the seeds of these abundant plant species, in this study site, they may limit too much increase of the predominant species and permit minor plant species to survive in the community. 6) Nonetheless, some seeds of Antidesma thawaitesianum, Nouclea subdita and Ficus spp. remained undigested in the feces of proboscis monkeys. The undigested seeds were small and relatively hard and were found in intact shape. Especially seeds of Ficus spp. were often found in feces when the proboscis monkeys often fed on its fruits, and Ficus species have been thought to be one of the most important plant species for a lot of wildlife. There is a possibility that proboscis monkeys may play the role of seed dispersal for a few plant species. 7) During 1,968 hours, the BE-Group moved within the range of 138.3 ha. The ranging of proboscis monkey was affected by the location of river crossing points and the availability of foods, in particular fruits. 8) The daily path length of BE-Group ranged from 220 m to 1,734 m (mean: 799 m) which was negatively correlated with fruit availability. The proboscis monkeys were apt to stay within a small range in fruit-abundant seasons. 9) BE-Group sometimes stayed within a limited area to frequently visit a particular tree which produced their favorite foods. Out of positively preferred trees or vines, Crudia reticulate, Cynometra ramiflora and Carallia brachiata could be such behavioral core trees. 10) Since the water level of the river had a statistically significant effect on the location of BE-Group’s sleeping site, when more than 3 m deep water covered the forest floor more than 1 km from both sides of the riverbank towards the inland in seasonal flood, the group slept inside the forest. It may be that the proboscis monkeys are not restricted to the riverbank, which has an uncluttered view for easily finding predators, because of reduced predation pressure by terrestrial animals during times when high water levels prevent predators from hunting. Thus, the feeding behavior of proboscis monkeys shows a high degree of fruit-eating (or seed-eating) in some seasons, and their extremely wide dietary diversity was demonstrated. Therefore, the ranging behaviors of proboscis monkeys were influenced by availability of fruits. The fruit-eating and fruit availability were one of the key factors to control the feeding and ranging behaviors of proboscis monkeys. In addition to those factors, ranging behaviors, including the sleeping sites selection of proboscis monkeys may be affected by predation pressure. In any case, the riverine forest of at least 800 m from the both river banks is evidently needed for the surviving of proboscis monkeys.
Conffering University: 北海道大学
Degree Report Number: 甲第8718号
Degree Level: 博士
Degree Discipline: 地球環境科学
Type: theses (doctoral)
Appears in Collections:学位論文 (Theses) > 博士 (地球環境科学)

Submitter: 松田 一希

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