The relationship between the Acoustic Complexity Index and avian species richness and diversity: a review

ABSTRACT Technologies to monitor species are constantly evolving including the use of acoustic recordings to determine species presence, activity patterns and population dynamics. The Acoustic Complexity Index (ACI) aims to determine ecologically relevant changes in the soundscape by measuring the variability within biotic sounds whilst remaining insensitive to anthrophony. Previous findings relating to this index and its correlations with avian species richness and diversity, environmental and anthropogenic factors were amalgamated in this review to guide the future use of this monitoring technique. A total of 25 papers were returned following a literature search in June 2020 targeting studies in which these relationships were analysed. Current literature shows inconclusive relationships between the ACI and avian species richness and diversity. Also, those studies analysing relationships between the index, environmental and anthropogenic factors provided contrasting results due to the lack of replication between studies. The future implementation of a standardised approach towards data collection should lead to more compelling conclusions. Relationships between the soundscape and the environment should be evaluated on an individual site basis due to the influence species composition has on the acoustic environment. Further study is required to determine the relationship between anthropogenic factors, the ACI and avian assemblages.