Unattended field measurement of bird source level

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.