OLD-WORLD MONKEY VOCALIZATIONS - ADAPTATION TO THE LOCAL HABITAT

Twenty-one representative vocalizations of two species of rain forest monkeys (blue monkeys, Cercopithecus mitis, and grey-cheeked mangabeys , Cercocebus albigena) and two species of savanna monkeys (vervet monk eys, Cercopithecus aethiops, and yellow baboons, Papio cynocephalus) w ere broadcast in both rain forest and savanna habitats. Broadcast sign als were re-recorded at distances of 12.5 and 100 m, digitized, and an alysed on a supercomputer to measure the magnitude of distortion of th e vocal repertoires of the savanna and forest monkeys in both the 'app ropriate' and 'inappropriate' habitats. Independent distortion analyse s were conducted in the time and frequency domains. The results showed that (1) distortion was strong following transmission distances of on ly 12.5 m in both habitats, (2) distortion scores were further increas ed, but only by a modest amount, when transmission distance was increa sed, (3) distortion scores were greater in the savanna habitat than in the rain forest habitat, (4) rain forest monkey calls were distorted less in the 'appropriate' rain forest habitat than in the 'inappropria te' savanna habitat, but (5) savanna monkey calls were similarly disto rted in both habitats. The results were consistent with the idea that the rain forest environment is generally more favourable for high-fide lity sound propagation, and that selection for reduced distortion has more strongly influenced the physical form of the vocal repertoire of the two rain forest species than that of the two savanna species. (C) 1995 The Association for the Study of Animal Behaviour