Eka adwitiya: Evolution of unimale social organisation in bonnet macaques

Publication Type:

Book Chapters


Proceedings of the Twenty-eighth Conference of the Ethological Society of India, Department of Zoology, Sarah Tucker College and Tamil Nadu Forest Department, Kalakad-Mundanthurai Tiger Reserve, Mundanthurai, p.110–115 (2003)




The bonnet macaque (Macaca radiata), a cercopithecine primate endemic to peninsular India, usually occurs in large multimale multifemale groups, typical of most cercopithecine species. This species lives in seasonal tropical deciduous forests and most females within a troop come into estrus synchronously; this has possibly led to, typically, a relatively greater proportion of males within groups and a promiscuous mating system. The northern subspecies of the bonnet macaque (M. r. radiata), however, may be remarkable amongst seasonally breeding macaques in having evolved, in recent years, a fairly high proportion of small, but stable, unimale troops within one particular population; 52 % of the troops in the Bandipur-Mudumalai wildlife sanctuaries of southern India are unimale. Demographic studies across populations indicate that, compared to multimale troops, unimale groups are relatively depleted in subadult and juvenile males, exhibit a unique female-biased birth sex ratio and display extensive female dispersal, all of which may have evolved in response to reproductive monopolisation by the solitary resident male. Several ecological factors, including food provisioning, may have led to the evolution of this social organisation, unique for a seasonally breeding cercopithecine primate. This extremely unusual phenomenon demonstrates the behavioural plasticity of a primate species and the value of demographic studies of multiple groups and populations.