Anthropogenic noise may be detrimental to many bird species, and manipulative experiments would help us understand these effects. We present the design and validation of a self-sustaining solarpowered broadcasting system that will allow researchers to disentangle acute or chronic effects of noise from effects of the presence of infrastructure, even in remote areas. We tested the broadcasting system using a case study on noise from oil well infrastructure in southern Alberta, Canada. Recordings from 2 types of oil wells were obtained and then broadcasted through 6 independent playback units continuously for a period of 3 months in 2013, at sites undisturbed by oil development. Sound measurements at real oil wells and at sites with broadcasting systems simulating the noise from these oil wells demonstrated that real and projected noise had very similar sound pressure levels, attenuation trends, and spectral composition. Throughout this long-term playback experiment, the system produced power and noise reliably and consistently. In conjunction with bird surveys, this experimental design and infrastructure can be used to allow researchers to dissociate the presence of anthropogenic development from associated noise, providing us with information that will help decrease the environmental impacts of human activities. Ó 2015 The Wildlife Society.
African forest elephants (Loxodonta cyclotis) are a critically endangered and visually cryptic species that inhabits Central African rainforests. Using a 1250 sq-km grid of 50 acoustic sensors in Republic of Congo, we investigated the landscape-scale behavioural response of forest elephants to poaching events. We detected eight automatic weapon fire events over 1.5 years of recording (2017)(2018)(2019). We examined detections of elephant vocalisations across grid sites within 10 km of the gunfire events in the 48 h surrounding the gunfire, and in paired 48-h control periods free of gunfire. Fewer vocalisations were detected before gunfire events than during control periods, suggesting elephants show behavioural responses to poacher presence before any shots are fired. Immediately following the gunfire events, a significant increase in elephant calls was detected, which may indicate increased communication to facilitate group cohesion and movement. Elevated call levels dropped to lower-than-baseline rates after several hours, suggestive of a sustained response. These patterns indicate forest elephants respond to both poacher presence and to gunfire events themselves. As these patterns may reflect behaviours that mediate population processes, conservation strategies should account for the potential of poaching to impact populations via indirect effects on nontarget elephants in the area.
The geography of biological sound is a largely unexplored topic that exists at the boundary of ecoacoustics and biogeography. Identification and characterization of patterns of biological sound and soundscape variation across the planet may provide insight into the potential for acoustics as a tool for biodiversity monitoring and conservation. Ecoacoustic indices are audio signal measurements that can be useful for revealing, characterizing, and comparing such soundscape patterns. Some of these indices, such as the Acoustic Complexity Index (ACI), have been shown to correlate with biodiversity and avian vocalization activity in some systems. The goal of this study was to investigate broad-scale trends in the ACI by testing whether the acoustic complexity of dawn chorus soundscapes follows the known latitudinal gradient in avian biodiversity. The ACI was calculated for dawn chorus recordings from 187 sites worldwide, spanning from -45.4° to 68.1° latitude. Acoustic complexity was expected to be highest near the equator and decrease with absolute latitude, tracking the general avian diversity gradient, because higher avian diversity should result in more elaborate dawn chorus soundscapes. However, the ACI did not track the general avian latitudinal diversity gradient. The results and potential explanations for this trend will be discussed.
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