From Soundwave to Soundscape: A Guide to Acoustic Research in Captive Animal Environments

Abstract

Sound is a complex feature of all environments, but captive animals' soundscapes (acoustic scenes) have been studied far less than those of wild animals. Furthermore, research across farms, laboratories, pet shelters, and zoos tends to focus on just one aspect of environmental sound measurement: its pressure level or intensity (in decibels). We review the state of the art of captive animal acoustic research and contrast this to the wild, highlighting new opportunities for the former to learn from the latter. We begin with a primer on sound, aimed at captive researchers and animal caregivers with an interest (rather than specific expertise) in acoustics. Then, we summarize animal acoustic research broadly split into measuring sound from animals, or their environment. We guide readers from soundwave to soundscape and through the burgeoning field of conservation technology, which offers new methods to capture multiple features of complex, gestalt soundscapes. Our review ends with suggestions for future research, and a practical guide to sound measurement in captive environments.

Pied tamarins change their vocal behavior in response to noise levels in the largest city in the Amazon

“…Unfortunately, we do not have estimates of parameters such as "annoyance" for nonhuman primates. What is considered "noise" may also depend on a species' hearing capacities (Clark & Dunn, 2022) and pied tamarin audiograms are currently unavailable. Even though we lack such clearcut values to establish what constitutes noise for pied tamarins, we found that when sound levels were relatively higher, the probability of pied tamarins emitting a long call increased.…”

“…It is important to note that in our study, we characterized noise in terms of amplitude. However, noise is complex and variable in terms of spectral and temporal signatures (Clark & Dunn, 2022; Gill et al, 2015; Neo et al, 2014). Howler monkeys, for instance, respond more to aerial traffic than other human‐produced noises (Gómez‐Espinosa et al, 2022).…”

Assessing the effect of zoo closure on the soundscape using multiple measures

“…Human presence can influence the soundscape experienced by animals in zoos. In general, sound sources in zoos can be separated into four broad categories: 1) permanent sources of anthropogenic sound, such as heating, ventilation, and air conditioning (HVAC) systems; 2) temporary anthropogenic sound from maintenance, construction, and other events; 3) human speech and footfall; and 4) sounds produced by other animals (Clark & Dunn 2022). Three of these four categories are related to human presence and anthropogenic sound sources, suggesting that the constant presence of humans is likely to have a significant impact on the soundscape.…”

“…As such, animals in captivity may experience soundscapes that differ from those in the wild (Lara & Vasconcelos 2019). In addition, the contributions of different sound sources are likely to differ among zoos and enclosures, and, therefore, soundscapes are also likely to vary among captive environments (Clark & Dunn 2022).…”

“…Despite its importance, the study of sound in zoos has lagged behind that in wild environments (Clark & Dunn 2022) and sound is less often considered than other features of the zoo environment (Binding et al 2020). Past work has focused mostly on measuring maximum sound pressure levels, which provide a quantification of environmental sound in decibels, most often in dB(A) (Clark & Dunn 2022).…”