Comparing the sampling performance of sound recorders versus point counts in bird surveys: a meta-analysis

1) Autonomous sound recording is a promising survey method for birds and other vocalising terrestrial wildlife. However, while there are clear advantages of sound recording methods over classical point counts conducted by humans, it has been difficult to quantitatively assess how they compare in their sampling performance. Quantitative comparisons of bird species richness between acoustic recorders and human point counts have previously been hampered by the differing and often unknown detection ranges among sampling methods. 2) We performed two meta-analyses based on 28 studies where bird point counts were paired with sound recordings at the same sampling sites. We compared alpha and gamma richness estimated by both survey methods after equalizing their effective detection ranges. We further assessed the influence of technical sound recording specifications (microphone signal-to-noise ratio, height, and number) on the bird sampling performance of sound recorders compared to unlimited ra...