Research methods for recording nocturnal birds were studied at 24 forests all around Japan, including semi-tropical to cool temperate zones, from mid May to mid June, 2007. We identified and collected data by ear from observation points for songs and calls of nocturnal birds between 19:00 and 04:00 hours. We also recorded the bird sounds with a Hi-MD (SONY MZ-RH1) recorder, and compared the results with the data collected by ear in the field.
The nocturnal bird species, except for Nycticorax nycticorax, were recorded more often during time periods after sunset and before sunrise. Cuculus fugax and Zoothera dauma were frequently recorded only before sunrise, and Otus scops and Strix uralensis were frequently recorded only after sunset. These results suggest that conducting surveys during both time periods is an effective method to record nocturnal avifauna.
Comparisons between direct/listening observations and sound recordings showed no significant differences in recording efficiency between the two methods for any nocturnal bird species. Sound recordings have some advantages over observations, for instance, allowing the possibility of reexamination of the records, including later identification of the sounds with the assistance of a specialist or by comparison to sound recordings. Therefore, sound recordings is recommended as a useful method to study nocturnal avifauna.