Date of Award
Master of Science (MS)
Andrew Caven, Gregory Pec, Larkin Powell
Acoustic indices;Avian monitoring;Bioacoustics;Grassland;Passive monitoring;Soundscape ecology
Acoustic indices are mathematical summaries of sound waves. Several researchers have tried to find relationships between them and vocal animal communities to use them as a passive monitoring method, as human-derived surveys are expensive, time-consuming, and suffer from observer bias. However, supplanting manual surveys with acoustic indices is a daunting task, considering effective indices for biological monitoring would need to differentiate biologically relevant sounds from the broader soundscape, including from human-derived (anthrophony) and earth-derived (geophony) sound. We collected avian community data and calculated six commonly used acoustic indices from acoustic recordings in the largest remaining intact lowland tallgrass prairie in the Central Platte River Valley throughout the breeding seasons of 2019-2021. Singular acoustic indices had only weak correlations with avian abundance, richness, Simpson diversity, and grassland species abundance. Of all avian community metrics, avian species richness was best predicted by the acoustic diversity index (ADI) when a measure of anthrophony was included in the model. The acoustic complexity index and normalized difference sound index also showed promise for use in models for grassland species abundance. We did not find strong evidence for the use of these acoustic indices as a proxy for traditional avian point count surveys, which diverges from much past research related to different ecosystems (i.e., tropical and temperature forests). Intact North American grasslands are declining due to increased agricultural use and urban sprawl, which likely increases the anthrophony in the remaining grasslands. This along with naturally more intense geophony from strong winds in the Great Plains likely creates a unique challenge for using acoustic indices to monitor populations of breeding grassland birds. However, model performance may be improved by including more refined measures of anthrophony, geophony, and habitat characteristics in future studies that examine utility of acoustic indices to track avian community trends in grassland ecosystems.
Ostrom, Bethany Lynn, "Monitoring Avian Populations with Acoustic Indices in the Central Platte River Valley" (2022). Biology Theses, Dissertations, and Student Creative Activity. 8.