This comprehensive overview of the behavioural and ecological diversity of the colobines shows that we have greatly expanded our understanding of the taxonomy, phylogeny, morphology, natural history, behaviour and conservation status of this subfamily since Glyn Davies and John Oates (1994) published the first book on them. Nonetheless, there remain many gaps in our knowledge. In Chapter 2, Roos highlights that our current understanding of the taxonomy of colobines should be considered preliminary because classifications are still largely based on phenotypic differences between museum specimens. Changes will likely need to be implemented as data become available on ecology, behaviour, morphology and especially genetics of many species and subspecies. Roos also notes that relative to the cercopithecines, colobines are neglected in study effort and thus new findings have the potential to expand our understanding of their taxonomic diversity, especially in genera such as Piliocolobus, Colobus, Presbytis, Trachypithecus and Semnopithecus that are found over large geographic areas and are species-rich.

Asian colobines make up close to half of all non-human primate species found in Asia. These monkeys have specialized dietary and habitat needs and are found in a wide range of habitat at different latitudinal and altitudinal zones. About two-thirds of Asian colobines are endemic to only one country, with the largest number of threatened species found in Indonesia, Vietnam and China. The highest percentage of colobine species are found in tropical rain forest and tropical moist deciduous forest that have correspondingly less areas remaining. Species that are found in specific habitats like karst limestones, flooded forests and highland forest are also particularly threatened. Expansion of agriculture, aquaculture and biological resource use, through hunting and trade are the current top threats to colobines. The successful conservation of these species would require that species-specific protection needs are met, as well as collaborative approaches to ensure better protection across their distribution ranges.

Colobinae, which includes more than 70 species grouped into 10 genera distributed throughout Asia and Africa, show a wide range of ecological and social traits. The colobines are generally forest-living and arboreal, which can make research on this often-elusive group difficult. Despite these challenges, our understanding of colobine behaviour, ecology and morphology has increased a great deal over the decades since the first research review on this primate subfamily was published by Davies and Oates (1994). While new research has demonstrated the incredible variation of colobine natural history, and the adaptability of this group, some colobine populations have declined and are now critically endangered. The Colobines brings together experts from around the world in an innovative volume that summarizes the current knowledge on colobine populations.

The odd-nosed monkeys represent a monophyletic group of phenotypically unique primates. They include five species of snub-nosed monkeys (Rhinopithecus), three species of doucs (Pygathrix) as well as simakobu (Simias concolor) and the proboscis monkey (Nasalis larvatus). These species are ecologically diverse and inhabit a gradient of environments in China and southeast Asia, from wet equatorial forests to alpine forests. Odd-nosed monkeys tend to be shy and difficult to habituate, and often range over relatively large areas. Many are also renowned for inhabiting remote areas with rugged terrain and inclement climatic conditions. It is thus not surprising that, until fairly recently, they were among the least studied and most enigmatic extant diurnal primates. However, since the beginning of the new millennium, an expanse of new and exciting research has been conducted on these colobines. In this chapter, we provide an overview of the current knowledge of the ecology and behaviour of odd-nosed monkeys and analyse some of their key behavioural traits and ecological adaptations in light of what is known about other colobines and primates as a whole.

Colobine monkeys differ from all other primates in having a foregut fermentation system featuring a complex, multi-chambered stomach with either three or four chambers where a commensal microbiome digests plant cell walls and possibly detoxifies defensive plant chemicals. Obtaining information on their morpho-physiological digestive traits, focusing on their forestomach physiology, is indispensable for understanding the mechanism underlying their ecology and behaviour. Additionally, such information would be useful for their zoological management as colobines have often been considered difficult to maintain healthy in captivity. There are new developments in our understanding of colobine digestive strategies, especially in terms of behavioural level, e.g., “rumination strategy” and resting posture, and physiological level, e.g., digesta flow and microbial patterns, though there has not been much progress in terms of clarifying their anatomical attributes since the previous 1994 review. In this chapter, we overview the recent findings on colobine digestive strategies, focusing on their forestomach.