Male Loud Calls in Macaca silenus and Presbytis johnii

Abstract

Analysis of the male loud calls of free-ranging lion-tailed macaques (Macaca silenus) and Nilgiri langurs (Presbytis johnii), two sympatric primates of the South Indian rain forests, revealed remarkable structural similarities: In both species the calls are uttered in long phrases with regular time structure, the units consisting of a tonal exhalation phase with high sound pressure and a more noisy inhalation phase with low sound pressure, but significant sound pressure variations. In both phases the energy is distributed over discrete frequency bands and concentrates on low-frequency ranges. These characteristics are consistent with essential bioacoustic requirements for long-distance propagation of vocal signals in rain forest habitat. Such type of loud call, being typical for langurs and mangabeys, is the first to be found in the Macaca genus. The two species, which belong to quite different genera, resemble each other not only in the vocal patterns of their loud calls, they also display striking similarities in habitus, exclusively arboreal dwelling habits, and in their social organization.