Using playback of vocalisations to survey the Nahan's francolin, a threatened African forest galliform

Abstract

Methods using playback of vocalisations have been widely used to survey elusive birds. Most of these methods suffer from the drawback that movement of birds is often elicited by the sound stimulus used, violating assumptions of distance sampling and generating unknown biases in resulting density estimates. Using playback survey data for a globally threatened forest galliform bird in Uganda, we found evidence of strong movement of birds toward the sound stimulus during playback surveys, and demonstrate that this caused a significant overestimation of bird density. We present a simple regression-based method for identifying and correcting this bias that is statistically robust and practical to implement for those surveying elusive forest birds. Based on our adjusted survey data, we estimate that about 40 000 Nahan's Francolins remain in Uganda.