Fallback Foods of Red Leaf Monkeys (Presbytis rubicunda) in Danum Valley, Borneo
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Animals in Southeast Asia must cope with long periods of fruit scarcity of unpredictable duration between irregular mast fruiting events. Long-term data are necessary to examine the effect of mast fruiting on diet, and particularly on the selection of fallback foods during periods of fruit scarcity. No such data is available for colobine monkeys, which may consume substantial amounts of fruits and seeds when available. We studied the diet of red leaf monkeys (Presbytis rubicunda, Colobinae) in Danum Valley, Sabah, northern Borneo, using 25 mo of behavioral observation, phenology and vegetation surveys, and chemical analysis to compare leaves eaten with nonfood leaves. The monkeys spent 46% of their feeding time on young leaves, 38% on seeds, 12% on whole fruits, 2.0% on flowers, 1.0% on bark, and 1.2% on pith. They spent more time feeding on seeds and whole fruit when fruit availability was high and fed on young leaves of Spatholobus macropterus (liana, Leguminosae) as fallback foods. This species was by far the most important food, constituting 27.9% of the total feeding time, and the feeding time on this species negatively correlated with fruit availability. Consumed leaves contained more protein than nonconsumed leaves, and variation in time spent feeding on different leaves was explained by their abundance. These results suggest that red leaf monkeys show essentially the same response to the supra-annual increase in fruit availability as sympatric monogastric primates, increasing their seed and whole-fruit consumption. However, they depended more on young leaves, in particular Spatholobus macropterus, as fallback foods during fruit-scarce periods than did gibbons or orangutans. Their selection of fallback food appeared to be due to both nutrition and abundance.
KeywordsDiet Fallback foods Functional response General flowering Spatholobus macropterus
This study would not have been possible without the hard work of our field assistants, Syamsudin Jail, Sharry bin Mustah, Saharudin Idos, Unding Jami, Sallehudin Jail, and Rayner Jupili. We thank the staff of the Danum Valley Field Centre and our colleagues there for their hospitality and help, in particular Jimmy Omar, Mike Bernadus, Glen Reynolds, Tomoko Kanamori, Noko Kuze, and Siew Te Wong. Constructive comments by Drs. Joanna Setchell, Oliver Shülke, and an anonymous reviewer greatly improved the manuscript. The Economy Planning Unit of Malaysia and the State of Sabah and the Danum Valley Management Committee of Yayasan Sabah permitted our study. This study was financed by the JSPS Core-to-Core Program (HOPE), the MEXT Grant-in-Aid for JSPS Overseas Fellows, Grant-in-Aid for Young Scientists (No. 20770195 and No. 22687002) to G. Hanya, Primate Society of Japan, the 21st Century COE Program (A14), and the Global COE Program “Formation of a Strategic Base for Biodiversity and Evolutionary Research: From Genome to Ecosystem”.
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