Variation in seed handling by two species of forest monkeys in Rwanda

We examined temporal variability in the handling and dispersal of seeds by two sympatric species of monkeys, the arboreal blue monkey (Cercopithecus mitis doggetti) and the more terrestrial mountain monkey (C.l'hoesti). Ten months of data on phenological patterns and foraging behavior, including details of seed handling based on scan sampling data, were combined with dung sample data to examine patterns of seed handling. The systematic scan sampling observations showed that blue monkeys and mountain monkeys alternated between acting predominately as seed droppers, seed predators, and seed defecators depending on fruit resource availability. All the mountain monkey dung samples examined contained intact seeds, and 94% of the blue monkey dung samples contained intact seeds. Both monkey species defecated a greater number of seeds per dung sample and larger-sized seeds than found elsewhere for Cercopithecus monkeys. We found a mean of 2.33 and 6.43 seeds > 2 mm in blue and mountain monkey dung samples, respectively. The mountain monkeys dispersed relatively higher numbers of seeds and frequented open, disturbed forest, suggesting that terrestrial forest monkeys have been overlooked as potentially important seed dispersal agents. The variability in the ways seeds were handled was dependent on the array of available food resources and may suggest that the monkeys exert weak selective pressures on fruit traits.