Acoustic Complexity Index (ACI)

AUS-AMR-LVG-ACI General Low confidence

Benchmark Value

No specific value — see range
Range: 1600 to 1800 index
Optimal Range: 1600 to 1800
Direction: Higher is desirable ↑
Form: OptimalRange

Scoring Curve

This curve shows how a field measurement for this indicator would score across all available benchmark forms in this context.

Evidence & Context

Based on visual inspection of Figure 4C in Scarpelli et al. (2021), the ACI values during the prominent dawn and dusk chorus peaks consistently fall within the range of 1600 to 1800.

Metric Definition:

Acoustic Complexity Index (ACI) calculated from a spectrogram representing sound frequency and intensity over time, summing absolute differences in intensity between adjacent time steps within each frequency bin.

Benchmark Definition:

The Acoustic Complexity Index (ACI) measures the variability of sound amplitudes over time, capturing complex, modulated biotic sounds in arid mountain rangelands under livestock grazing and pasture use.

Justification:

The benchmark is a derived estimate from a proxy site (Bowra Wildlife Sanctuary) in a semi-arid biome, estimated visually from a published graph, and subject to limitations of the ACI metric.

Sources (1)

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Multi-Index Ecoacoustics Analysis for Terrestrial Soundscapes: A New Semi-Automated Approach Using Time-Series Motif Discovery and Random Forest Classification - Frontiers Journal

Landscape monitoring in forests: a wildlife ecologist's perspective - Taylor & Francis Online, accessed July 20, 2025,

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Supporting Sources (48)

Additional references from the underlying research that informed this benchmark.

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(PDF) Diversity favours the old: Metrics of avian diversity increase in aging regrowth Acacia woodlands of semi-arid eastern Australia - ResearchGate
Contextual Support Journal

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Methodology Source Journal

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A new methodology to infer the singing activity of an avian community: The Acoustic Complexity Index (ACI) | Request PDF - ResearchGate
Methodology Source Journal

A new methodology to infer the singing activity of an avian community: The Acoustic Complexity Index (ACI) | Request PDF - ResearchGate

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Preview of Acoustic data now available for Bowra Wildlife Sanctuary
Acoustic data now available for Bowra Wildlife Sanctuary
Contextual Support GreyLiterature

Acoustic data now available for Bowra Wildlife Sanctuary

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Acoustic indices as proxies for biodiversity: a meta-analysis - PubMed
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Acoustic indices as proxies for biodiversity: a meta-analysis - PubMed

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Acoustic indices as proxies for biodiversity: a meta‐analysis - PMC - PubMed Central, accessed July 22, 2025,
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SELECTING APPROPRIATE ACOUSTIC INDICES FOR BIODIVERSITY ASSESSMENTS IN DIFFERENT ACOUSTIC ENVIRONMENTS, accessed July 20, 2025,

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Preview of Acoustic Indices for Biodiversity Assessment and Landscape Investigation | Request PDF
Acoustic Indices for Biodiversity Assessment and Landscape Investigation | Request PDF
Contextual Support

Full article: The relationship between the Acoustic Complexity Index and avian species richness and diversity: a review - Taylor & Francis Online, accessed July 20, 2025,

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acoustic_complexity Acoustic Complexity Index - RDocumentation
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Contextual Support Journal

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Bowra Wildlife Sanctuary - Outback Queensland
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Preview of Bowra Wildlife Sanctuary - Queensland
Bowra Wildlife Sanctuary - Queensland
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Bowra Wildlife Sanctuary Visitor Program - Birds Queensland
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Bowra Wildlife Sanctuary Visitor Program - Birds Queensland

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Preview of Ecoacoustics - Eco Logical Australia
Ecoacoustics - Eco Logical Australia
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Ecoacoustics: acoustic sensing for biodiversity monitoring at scale - ResearchGate
Contextual Support

Ecoacoustics: acoustic sensing for biodiversity monitoring at scale - ResearchGate

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Effectiveness of acoustic indices as indicators of vertebrate biodiversity - ResearchGate, accessed July 22, 2025,
Contextual Support Journal

Bioacoustics and AI help scientists listen in on elusive Australian cockatoos

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Contextual Support Government

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Full article: The relationship between the Acoustic Complexity Index and avian species richness and diversity: a review - Taylor & Francis Online, accessed July 22, 2025,
Contextual Support

The relationship between the Acoustic Complexity Index and avian species richness and diversity: a review - Taylor & Francis Online, accessed August 28, 2025

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Impact of acoustic index parameters on soundscape comparisons
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Key Issues for Realizing Open Ecoacoustic Monitoring in Australia - Frontiers
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Listen up: new technologies for sound biodiversity monitoring - TERN Australia
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Multi-Index Ecoacoustics Analysis for Terrestrial Soundscapes: A New Semi-Automated Approach Using Time-Series Motif Discovery and Random Forest Classification - ResearchGate
Direct Evidence

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Spatial and temporal variation of bird dawn chorus and successive acoustic morning activity in a Mediterranean landscape
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Understanding how acoustic indices reflect soundscape patterns is key... - ResearchGate
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Who Eats the Grass? Grazing Pressure and Interactions Between Wild Kangaroos, Feral Goats and Rabbits, and Domestic Sheep on an Arid Australian Rangeland - MDPI
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Who Eats the Grass? Grazing Pressure and Interactions Between Wild Kangaroos, Feral Goats and Rabbits, and Domestic Sheep on an Arid Australian Rangeland - MDPI

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Context

  • Region Australia
  • Biome Arid Mountain Ranges & Uplands
  • Land Use Livestock Grazing & Pasture
  • Assessment Pristine Reference
  • Evidence Type ReferenceCondition

Lifecycle

  • Status Active
  • Version 1
  • Effective From 17 Mar 2026

Notes

A single ACI value is insufficient as an indicator; a healthy system is characterized by strong, distinct ACI peaks during dawn and dusk avian choruses. High values can be misleading due to geophony or insect noise. The diel pattern is more informative than absolute values. No upper detrimental threshold — higher values are always better up to natural saturation.