Bat echolocation in continental China: a systematic review and first acoustic identification key for the country

The development of increasingly affordable ultrasonic detectors and automatic classifiers has increasingly boosted the use of acoustic recording of echolocation calls to survey bats all over the world. Echolocation call keys are crucial to reliably classify acoustic recordings, but those are not available for many regions, such as China. In the present study, we conducted a systematic review of bat echolocation studies across continental China and developed an acoustic identification key. Based on 130 studies, published from 1999 to 2020, we obtained echolocation parameters from 64 bat species (47.4% of the total echolocating species known from the country). This review highlights the lack of echolocation references from continental China for 71 species, from which, the echolocation of 21 has never been described. Additionally, we developed the Bat Knowledge Index, an indicator that allows the identification of key priority areas for future research on bat acoustics and geographic biases in the existing studies, further highlighting the lack of studies in the northwestern regions of the country. The compiled identification key provides easy-to-follow identification steps to classify the echolocation calls of 114 species (84.5% of all Chinese echolocating species) to either species (11.4%) or phonic group level (88.6%). This key represents a useful baseline tool and a further step to increase bioacoustic studies’ suitability in China.