American Journal of Primatology 73:335–346 (2011) RESEARCH ARTICLE Resource Partitioning in Sympatric Langurs and Macaques in Tropical Rainforests of the Central Western Ghats, South India MEWA SINGH 1Ã , KULADEEP ROY 1 , AND MRIDULA SINGH 2 1 Biopsychology Laboratory, University of Mysore, Mysore, India 2 Maharaja’s College, University of Mysore, Mysore, India In a competitive sympatric association, coexisting species may try to reduce interspecific interactions as well as competition for similar resources by several ecological and behavioral practices. We studied resource utilization of three sympatric primate species namely, lion-tailed macaques (Macaca silenus), bonnet macaques (M. radiata) and Hanuman langurs (Semnopithecus entellus) in a tropical rainforest of the central Western Ghats, south India. We studied resource use, tree-height use, foraging height, substrate use when consuming animal prey and interspecific interactions. The results revealed that across the year, there was very limited niche overlap in diet between each species-pair. Each primate species largely depended on different plant species or different plant parts and phenophases from shared plant species. Primate species used different heights for foraging, and the two macaque species searched different substrates when foraging on animal prey. We also recorded season-wise resource abundance for the resources shared by these three primate species. While there was low dietary overlap during the dry season (a period of relatively low resource abundance), there was high dietary overlap between the two macaque species during the wet season (a period of high resource abundance for the shared resources). We observed only a few interspecific interactions. None of these were agonistic, even during the period of high niche overlap. This suggests that the sympatric primate species in this region are characterized by little or no contest competition. Unlike in some other regions of the Western Ghats, the lack of interspecific feeding competition appears to allow these primates, especially the macaques, to remain sympatric year-round. Am. J. Primatol. 73:335–346, 2011. r 2010 Wiley-Liss, Inc. Key words: lion-tailed macaque; bonnet macaque; Hanuman langur; niche overlap; interspecific interaction; coexistence INTRODUCTION The presence of two or more species of animals that travel, rest or feed together in the same location at a rate greater than predicted by chance is referred to as a polyspecific association. Mutual behavioral attraction, attraction to common resources or a location, or just ‘‘chance’’ may result in spatial associations between different animal species [Waser, 1984]. Polyspecific associations may be beneficial if they result in an increased efficiency in harvesting and defending resources [Cords, 2000] and detecting predators [Buzzard, 2010]. For example, groups of Callimico goeldii remained in proximity or in vocal contact with groups of Saguinus fuscicollis and S. labiatus during 7% of the day. When in association with Saguinus in wet season, C. goeldii spent 13% of time co-feeding as compared to only 2% in dry season. Callimico used the middle canopy 62% while in association as compared to 52% when they were a single species group [Porter, 2001]. Porter [2001] argued that Callimico received feeding and possibly predator detection advantages when part of a polyspecific association. However, in other cases, species that are closely related or have largely similar food habits, such as consumption of fruits by lion- tailed macaques and bonnet macaques, may compete for resources [Sushma & Singh, 2006]. Under these conditions, we expected some form of niche separa- tion. For example, based on a 16-month field investigation, when in polyspecific groups, Cerco- pithecus diana was found to feed and travel in the upper canopy in 88% scans, whereas C. campbelli and C. petaurista fed and traveled principally in the lower canopy. In contrast, at sites where C. campbelli and C. petaurista are present and C. diana is absent, Published online 30 November 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ajp.20900 Received 25 July 2010; revised 24 October 2010; revision accepted 24 October 2010 Contract grant sponsor: Department of Science and Technology, Government of India; Contract grant number: SR/SO/AS-35/ 2004. Ã Correspondence to: Mewa Singh, Biopsychology Laboratory, University of Mysore, Mysore-570006, India. E-mail: mewasingh@bsnl.in r r 2010 Wiley-Liss, Inc.