Accuracy of an acoustic location system for monitoring the position of duetting songbirds in tropical forest

Abstract

A field test was conducted on the accuracy of an eight-microphone acoustic location system designed to triangulate the position of duetting rufous-and-white wrens (Thryothorus rufalbus) in Costa Rica's humid evergreen forest. Eight microphones were set up in the breeding territories of 20 pairs of wrens, with an average intermicrophone distance of 75.2+/-2.6 m. The array of microphones was used to record antiphonal duets broadcast through stereo loudspeakers. The positions of the loudspeakers were then estimated by evaluating the delay with which the eight microphones recorded the broadcast sounds. Position estimates were compared to coordinates surveyed with a global-positioning system (GPS). The acoustic location system estimated the position of loudspeakers with an error of 2.82+/-0.26 m and calculated the distance between the "male" and "female" loudspeakers with an error of 2.12+/-0.42 m. Given the large range of distances between duetting birds, this relatively low level of error demonstrates that the acoustic location system is a useful tool for studying avian duets. Location error was influenced partly by the difficulties inherent in collecting high accuracy GPS coordinates of microphone positions underneath a lush tropical canopy and partly by the complicating influence of irregular topography and thick vegetation on sound transmission.

Direction-of-arrival estimation of animal vocalizations for monitoring animal behavior and improving estimates of abundance

“…Both methods are expected to produce more accurate location estimates when using a larger number of nodes. A further consideration is that TDOA approaches are typically limited in their ability to estimate the vertical position of a vocalizing animal, and for this reason are generally used for twodimensional localization (Janik et al 2000, Laurinolli et al 2003, Bower and Clark 2005, Mennill et al 2006, Collier et al 2010, but see Stepanian et al 2016). Our results suggest that DOAbased localizations should be accurate in both the horizontal and vertical dimensions (Fig.…”

“…Localization using TDOA, in contrast, requires synchronization between the nodes in an array. This has been accomplished in the past either by wiring the nodes together, an expensive and labor-intensive task (Mennill et al 2006), or, more recently, through the use of GPS (Mennill et al 2012) or wireless communication (Collier et al 2010). Any errors in the synchronization between nodes will affect the accuracy of TDOAbased location estimates.…”

“…A benefit of TDOA localization is that each node in an array can comprise just a single microphone (e.g., Mennill et al 2006), while DOA estimation requires at least three microphones per node (in this study, four were used). The requirement of more microphones per node for DOA is at least partially offset by the fewer number of nodes required to estimate locations using DOA: TDOA requires at least three distinct nodes to estimate an absolute location, while DOA can accomplish this with as few as one selfcontained unit.…”

“…Localization has most commonly been accomplished by assessing differences in the arrival time of a signal at multiple, widely spaced microphones, a technique commonly referred to as the time-differences-ofarrival (TDOA) approach to localization (Stafford et al 1998, Janik et al 2000, Bower and Clark 2005, Mennill et al 2006, Collier et al 2010, Stepanian et al 2016. The microphone picking up the sound first is presumed to be closest to the sound source, and the relative time delay of the signal at all other microphones is used to estimate the absolute location based on the speed of sound transmission through the relevant medium, i.e., air or water.…”

“…Technological advances hold promise to improve coverage through the adoption of autonomous sensors for the collection of biological data (Porter et al 2009). One type of automated sensor is the autonomous recording unit (ARU) for passive acoustic data collection, which is increasingly being employed for studies on marine mammals (Stafford et al 1998, Laurinolli et al 2003, Bonnel et al 2008, Mouy et al 2012, Rone et al 2012, terrestrial mammals (Heinicke et al 2015), bats (MacSwiney González et al 2008), and birds (Mennill et al 2006, Brandes 2008, Collier et al 2010. ARUs confer several advantages over traditional methods of observation.…”