Using Extended-Duration Audio Recordings to Survey Avian Species

Point-count surveys are widely used to infer avian presence and estimate species richness. Advancements in bioacoustic technology enable automated surveys that can supplement human-based point-count surveys with expanded temporal and spatial coverage. We surveyed birds in 13 Sierra Nevada and Cascade Range (CA, USA) montane meadows from May to August 2006 using 8 point-count surveys and automated audio recorders (ARU) to compare species richness between the 2 methods and evaluate the use of ARUs as a monitoring tool. We analyzed species richness using 30 minutes of ARU data per point and 2 point-count surveys. Automated audio-recorder data revealed 14 species per meadow (56 species total) while point counts detected 16 species per meadow (67 species total). Automated audio recorders provided > 1,100 additional hours of data with personnel effort similar to 2 point-count surveys. An asymptote in species richness was reached for every meadow using ARU data and 8 of 13 meadows using 2 point-count surveys. We detected 81 species during all 8 point-count surveys. We used SonoBird (DNDesign, Arcata, CA) software to search for 24 species detected by point-count surveys but not in the manually sampled subset of audio files. We detected 22 additional species, bringing the total audio-file species detections to 85, 4 more than detected by 8 point-count surveys. We conclude that audio recordings and analysis provide an alternative to avian point-count surveys or as a supplement to increase their accuracy, particularly over larger temporal and spatial scales, or for species with low detectability. (C) 2012 The Wildlife Society.