Accuracy of bittern location by acoustic triangulation

Abstract

Abstract Ecological studies and population surveys sometimes require information on the position of individuals. Because many birds are more audible than visible, we tested the potential of acoustic triangulation for locating Great Bitterns (Botaurus stellaris) within extensive reed marshes in the Camargue, France. During the breeding season, and predominantly at dawn, male bitterns produce a series of loud calls (booms). In the field, the direction of booming was estimated with a bearing compass by an observer walking along a linear path at the reedbed edge, taking enough measurements to cover a 90° wide angle between the first and last bearing. We used a probability model with an Andrews estimator to locate each bittern based on the intersection point of the bearings taken in the field. Bearing error was estimated by comparing these bearings with those derived from the real or estimated bird position. In a first experiment, we identified the factors influencing the variation in bearing error using six o...