Passive Acoustic Monitoring application to evaluate the vocal behavior of wild howler monkeys (Alouatta guariba clamitans)

Abstract

Passive Acoustic Monitoring (PAM) provides the way to feature the status, presence and trends of species’ distribution in different landscapes, under different environmental conditions. The howler monkeys are known for investing a long time and energy in the vocal type known as roar, an important vocal type for intra- and inter-group dynamics. The aim of the present study was to evaluate the detection, distribution and vocal behavior of wild howler monkeys based on the PAM methodology due to the need of having a fast and effective method to evaluate this species’ population presence and status given the successive yellow fever outbreaks lethally affecting it. The study was carried out at Fontes do Ipiranga State Park, Southeastern São Paulo City, Brazil. The evaluation of howler monkeys roar vocal behavior’s temporal pattern was carried out by taking into consideration the number of roaring events counted based on time. Vocalization occurrences observed between stations were compared to express the roaring events on an hourly basis. In total, 1,531 hours of recordings were analyzed and it allowed detecting roars in all PAM stations. The number of roaring events ranged from 71 to 142 per station. The present study has shown the useful application of PAM to accurately detect the presence of howler monkey groups based on vocal behavior. Furthermore, this method helps assessing groups’ distribution and daily occurrence, besides giving tips about how they are distributed in the area based on their handling ability.