A multi-level society comprised of one-male and multi-male core units in an African colobine (Colobus angolensis ruwenzorii)

Abstract

A few mammalian species exhibit complex, nested social organizations, termed multi-level societies. Among nonhuman primates, multi-level societies have been confirmed in several African papionin and Asian colobine species. Using data on individually-recognized Rwenzori Angolan colobus at Lake Nabugabo, Uganda, we document the first multi-level society in an African colobine. The study band comprised up to 135 individuals living in 12 socially and spatially distinct core units that ranged in size from 4 to 23 individuals. These core units shared a home range, and fissioned and fused throughout the day. Using the association indices between core units, we employed hierarchical cluster analyses and permutation tests to show that some core units clustered into clans. Thus, we confirm three tiers of social organization for Rwenzori Angolan colobus: core unit, clan, and band. The social organization of this subspecies is unlike any reported previously in a nonhuman primate, with about half the core units containing a single adult male and the others containing multiple reproductive adult males. Preliminary data show males to transfer within the band and female to transfer outside of the band, which suggests that, like Hamadryas baboons, this subspecies could provide insight into the selective pressures underlying hominin social organization.