Variation in dawn chorus acoustic complexity across a global latitudinal gradient

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.