Autonomous bird sound recording outperforms direct human observation: Synthesis and new evidence

1) Autonomous sound recording techniques have gained considerable traction in the last decade, but the question still remains whether they can replace human observation surveys to sample some animal taxa. Especially bird survey methods have been tested using classical point counts and autonomous sound recording techniques. 2) We review the latest information by comparing both survey methods' standardization, verifiability, sampling completeness, data types, compatibility, and practicality by means of a systematic review and a meta-analysis of alpha and gamma species richness levels sampled by both methods across 20 separate studies. 3) Although sound recording surveys have hitherto not enjoyed the most effective setups, they yield very similar results in terms of alpha and gamma species richness. We also reveal the crucial importance of the microphone (high signal-to-noise ratio) as the sensor that replaces human senses. 4) We discuss key differences between both methods, while richness estimates are closely related and 81% of all species were detected by both methods. Sound recording techniques provide a more powerful and promising tool to monitor birds in a standardized, verifiable, and exhaustive way against the golden standard of point counts. Advantages include the capability of sampling continuously through day or season and of difficult-to-reach regions in an autonomous way, avoidance of observer bias and human disturbance effects and higher detection probability of rare species due to extensive recordings.