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Title: Orangutan feeding behaviour in Sabangau, Central Kalimantan
Author: Harrison, Mark Edward
ISNI:       0000 0004 2708 4208
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2009
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Detailed studies of energy/nutrient acquisition and food selection have been completed for both African apes and orangutans in mast-fruiting dipterocarp forests, but, to date, no studies of this type have been completed on orangutans in non-masting forests, which experience more muted fluctuations in fruit availability. Such studies may be instructive in understanding whether the observations on orangutans in masting habitats are specific to orangutans, or specific only to orangutans in masting habitats. To investigate this, orangutan diet composition, energy intake, food selection and behaviour were studied in relation to orangutan fruit/flower availability, and chemical and non-chemical food properties, in the Sabangau peat-swamp forest, Central Kalimantan from July 2005-June2007. All data were collected using standard methods, and comparisons made with published data on orangutans in mast-fruiting habitats and on African apes. Orangutan fruit availability in Sabangau was lower and less variable than in the masting forests of Gunung Palung National Park, West Kalimantan. Daily energy intake was below requirements in most months, and similar to periods of very low food availability between mast-fruiting events in Gunung Palung. Mechanisms through which orangutans may have survived this prolonged energetic shortfall are suggested. In addition, unlike in Gunung Palung, where energy intake and fruit availability are tightly linked in both sexes, the only age-sex class in which energy intake in Sabangau was related to fruit availability was flanged males. Although selection of preferred vs. fall-back food types in Sabangau appears to be governed at least partially by the expected rate of energy returns, fruit and flower selectivity rank appears better explained by food quality: the best multivariate model of adult female fruit selectivity rank contained only protein/fibre ratio, and bivariate correlations between fruit-pulp selectivity rank and protein/fibre ratio were also significant for flanged males. Furthermore, adult female and flanged male fruit selectivity rank was negatively affected by fibre, weight or energy intake in at least one bivariate analysis. This is suggested to represent selection against ingestion of large amounts of relatively indigestible fibre, and implies that maximising dietary quality, rather than energy intake, as has been suggested in masting forests in Borneo, may be the optimal feeding strategy for orangutans in habitats where fruit quality is relatively poor and/or fruit availability is relatively consistent. Finally, compared to orangutans in Bornean masting forests, Sabangau orangutans exhibit a relative lack of modifications in nonfeeding behaviours in response to reductions in preferred food availability. These results suggest that, compared to masting forests in Borneo, lower mean quality and quantity of fruit, and lower variability in these parameters, in the Sabangau peat swamps leads to important differences in feeding behaviour between these habitat types. When compared to data on orangutans in other sites and African great apes, these observations are compatible with a graded-response hypothesis, in which the less predictable the availability of high-energy fruit in a site: (1) the stronger the relationship between fruit availability, fruit consumption and energy intake, (2) the more food is selected based on energy content, and (3) the stronger the influence of fluctuations in fruit availability on behaviour and, ultimately, probably also female reproduction. The implications of these findings are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral