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1.  Leaf Selection by Two Bornean Colobine Monkeys in Relation to Plant Chemistry and Abundance 
Scientific Reports  2013;3:1873.
Focusing on the chemical basis of dietary selection while investigating the nutritional ecology of animals helps understand their feeding biology. It is also important to consider food abundance/biomass while studying the mechanism of animal food selection. We studied leaf selection in two Bornean folivorous primates in relation to plant chemistry and abundance: proboscis monkeys inhabiting a secondary riverine forest and red leaf monkeys inhabiting a primary forest. Both species tended to prefer leaves containing higher protein levels, although more abundant plant species were chosen within the preferred species, probably to maximise energy gain per unit time. However, the two species showed clear differences in their detailed feeding strategy. Red leaf monkeys strictly chose to consume young leaves to adapt to the poor nutritional environment of the primary forest, whereas proboscis monkeys were not highly selective because of the better quality of its common food in the riverine forest.
doi:10.1038/srep01873
PMCID: PMC3660720  PMID: 23695180
2.  Regurgitation and remastication in the foregut-fermenting proboscis monkey (Nasalis larvatus) 
Biology Letters  2011;7(5):786-789.
Although foregut fermentation is often equated with rumination in the literature, functional ruminants (ruminants, camelids) differ fundamentally from non-ruminant foregut fermenters (e.g. macropods, hippos, peccaries). They combine foregut fermentation with a sorting mechanism that allows them to remasticate large particles and clear their foregut quickly of digested particles; thus, they do not only achieve high degrees of particle size reduction but also comparatively high food intakes. Regurgitation and remastication of stomach contents have been described sporadically in several non-ruminant, non-primate herbivores. However, this so-called ‘merycism’ apparently does not occur as consistently as in ruminants. Here, to our knowledge we report, for the first time, regurgitation and remastication in 23 free-ranging individuals of a primate species, the foregut-fermenting proboscis monkey (Nasalis larvatus). In one male that was observed continuously during 169 days, the behaviour was observed on 11 different days occurring mostly in the morning, and was associated with significantly higher proportions of daily feeding time than on days when it was not observed. This observation is consistent with the concept that intensified mastication allows higher food intake without compromising digestive efficiency, and represents an expansion of the known physiological primate repertoire that converges with a strategy usually associated with ruminants only.
doi:10.1098/rsbl.2011.0197
PMCID: PMC3169055  PMID: 21450728
rumination; merycism; foregut fermentation; herbivory; food intake
3.  Aerial Surveys Give New Estimates for Orangutans in Sabah, Malaysia 
PLoS Biology  2004;3(1):e3.
Great apes are threatened with extinction, but precise information about the distribution and size of most populations is currently lacking. We conducted orangutan nest counts in the Malaysian state of Sabah (North Borneo), using a combination of ground and helicopter surveys, and provided a way to estimate the current distribution and size of the populations living throughout the entire state. We show that the number of nests detected during aerial surveys is directly related to the estimated true animal density and that a helicopter is an efficient tool to provide robust estimates of orangutan numbers. Our results reveal that with a total estimated population size of about 11,000 individuals, Sabah is one of the main strongholds for orangutans in North Borneo. More than 60% of orangutans living in the state occur outside protected areas, in production forests that have been through several rounds of logging extraction and are still exploited for timber. The role of exploited forests clearly merits further investigation for orangutan conservation in Sabah.
A new aerial method for surveying orangutan densities provides robust estimates of their number and could be used for large- scale surveying of great ape populations in Asia and Africa
doi:10.1371/journal.pbio.0030003
PMCID: PMC534813  PMID: 15630475

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