Unattended field measurement of bird source level

TL;DR

This study demonstrates a field method using a calibrated microphone array to measure bird sound power levels, providing new data and enabling unattended, non-visual acoustic monitoring of bird species.

Contribution

Introduces a novel field measurement technique for bird sound power levels using a calibrated microphone array, minimizing ground reflection effects and allowing unattended data collection.

Findings

Successfully measured sound power levels for 4 bird species.

Validated the feasibility of unattended, in-situ bird sound power measurements.

Provided new data on bird source levels to aid bioacoustic research.

Abstract

Sound power levels or so-called source levels are essential quantities when it comes to evaluating the active space of bird species, both in the study of animal communication and when designing bioacoustic monitoring schemes. However, little data is available in the literature. In this paper I demonstrate the feasibility of the measurement of apparent sound power in the field for bird species by using a calibrated 4-microphone horizontal array deployed on the ground. Time differences of arrival allow for the location of the sound source. Assuming a point source, the apparent sound power level is estimated after correcting for ground reflection and spherical divergence but cannot be corrected for source directivity. The benefits of my approach that is inspired from engineering measurement standards for elevated sound sources, is to minimize the contribution from ground reflections and to allow for unattended measurements, or measurements when the bird is not visible, owing to either foliage or obscurity. Moreover, my paper brings new data on sound power for 4 species of birds.