The use of acoustic indices to assess avian biodiversity in the Chornobyl exclusion zone, Ukraine

Following the 1986 accident at the Chornobyl Nuclear Power Plant, researchers have had a unique opportunity to investigate the effects of radiation on a wide range of taxa, including mammals, birds, and invertebrates. Among these, birds have been one of the most extensively studied groups within the Chornobyl Exclusion Zone, with the majority of studies reporting adverse effects of radiation exposure. These investigations have primarily relied on traditional avian ecology methods, such as point counts and line transects. However, such methods are subject to limitations, including the absence of independent verification and the potential for unconscious observer bias. Passive acoustic monitoring (PAM) provides permanent, verifiable records of the soundscape, reducing reliance on observer based methods. Acoustic indices, quantitative measures of soundscape structure, then offer an efficient and objective way to assess patterns across sites and times. With the growing adoption of PAM in biodiversity research, this study employed four acoustic indices – Acoustic Complexity Index, Acoustic Diversity Index, Acoustic Evenness Index, and Bioacoustic Index - to assess bird diversity across three broadly defined contamination zones within the Chornobyl Exclusion Zone. Recordings were sampled for two minutes every hour during September 2015 and May 2016. The results revealed that both time category and recording month significantly influenced all four acoustic indices, whereas total estimated absorbed radiation dose rate had no significant effect. This research marks one of the first terrestrial applications of ecoacoustics within the field of radioecology and offers insights into avian biodiversity patterns in the Chornobyl Exclusion Zone.