The influence of anthropogenic noise on the behavior of male mantled howler monkeys

Abstract

Anthropogenic noise is increasingly disturbing natural soundscapes and affecting the physiology, behavior, and fitness of wildlife. However, our knowledge about the impact of anthropogenic noise on wild primates is scant. Here, we assess the effects of anthropogenic noise on the behavior of male mantled howler monkeys (Alouatta palliata). Specifically, we describe the types, rates, and sound pressure level (SPL) of anthropogenic noise that occurs in areas inhabited by mantled howler monkeys and determine if the behavioral responses of males to anthropogenic noise are influenced by noise attributes. For 1 year (1753 h), we characterized anthropogenic noise in the Los Tuxtlas Biosphere Reserve (Veracruz, Mexico) and studied the behavior of males belonging to five groups. Anthropogenic noise was common, diverse, and varied among areas in terms of rate, type, and SPL. Males did not display behavioral responses toward most (60%) anthropogenic noises, but were more likely to respond to certain noise types (e.g., aerial traffic) and toward noise with high SPL.Group identity influenced the likelihood of displaying behavioral responses to noise.The most common behavioral responses were vocalizations and vigilance. Males vocalized in response to noise with high SPL, although this relationship depended on group identity. The effect of the number of noises on vocalizations also varied among groups. Males were more likely to display vigilance toward high SPL and infrequent noise, but, again, these relationships varied among groups. In sum, anthropogenic noise is pervasive in areas inhabited by mantled howler monkeys and influences male behavior. Experience and frequency of exposure may modulate the behavioral responses of male mantled howler monkeys to noise and explain the group differences.

Noise intensity modulates the responses of mantled howler monkeys to anthropophony

“…Our study is not the first to assess the effects of anthropogenic noise on wild primates. Besides previous correlational evidence on fGCM and behavioral responses of mantled howler monkeys to noise (Cañadas-Santiago et al, 2020;Gómez-Espinosa et al, 2022), other species have been reported to change vocalization patterns and avoid areas with more noise (e.g., Duarte et al, 2011;Sheehan & Papworth, 2019). Those studies, however, did not establish which noise attribute was linked to primate responses (e.g., noise intensity vs. frequency), precluding precise interpretations.…”

“…Over the past 60 years the area has been highly disturbed by human activities and consists of a mosaic of original and secondary forests, agricultural fields, and human settlements (Von Thaden et al, 2020). We focused on five groups of mantled howler monkeys that we had studied for at least 6 years (mean ± standard deviation [SD] = 16.6 ± 6.8 years; Gómez‐Espinosa et al, 2022). All groups were habituated to the presence of researchers, and we identified subjects by natural markings in their fur and other physical traits, such as scars, broken fingers, and facial features.…”

“…SPL is the pressure of sound waves within a certain frequency range in the air relative to a reference pressure. The two SPL treatments correspond to the minimum and maximum values of naturally occurring chainsaw noise recorded in a previous study (Gómez-Espinosa et al, 2022). In a similar environment to those where we would conduct the experiments, we placed the speaker at ground level and recorded SLP with a sound meter (TN-ST106, Tenmars, Taiwan; measuring range = 30-130 dB; sampling frequency = 20.8 μS (48 kHz); frequency band = 10Hz-16 kHz) at increasing distances (assessed with a measuring tape) from the speaker while regulating the speaker's volume so that chainsaw noise sounded natural.…”

“…For instance, fecal glucocorticoid metabolite concentrations and time spent in vigilance are more influenced by the occurrence of anthropogenic noise than by the amount of available forest. Second, most anthropogenic noises are not associated with a behavioral response by mantled howler monkeys, but the response likelihood depends on noise type, frequency, and intensity such that, for instance, vigilance and vocalizations are more frequent with increasing noise intensity (Gómez‐Espinosa et al, 2022). Mantled howler monkeys seem therefore to be reactive to anthropogenic noise, although the available correlational data does not allow establishing which noise attributes underly their physiological and behavioral responses.…”

One step forward, two steps backward: The frailty of howler monkey conservation in Los Tuxtlas, Mexico

“…A group of mantled howler monkeys has lived in a riparian fragment located to the west of the quarry at least since 1995 (Estrada et al, 1999) At the time of writing, mantled howler monkey groups had not left the area, probably because the extraction of rock focused mostly on steep slopes with scrub vegetation that howler monkeys do not regularly use. Still, some trees plunged and the remarkable increase in the number of people, vehicles, and noise in the area may affect the behavior and physiology of mantled howler monkeys, as previously demonstrated (Cañadas-Santiago et al, 2020;Gómez-Espinosa et al, 2022). Additionally, there are unofficial accounts that the mining operations will expand in the future, which could critically affect the vegetation in the habitat of mantled howler monkeys.…”