Niche Environment and Heritage was commissioned by the Forestry Corporation of New South Wales to determine the feasibility of using SongMeters (a commercially-available sound recording device) to replace the field deployment of experienced bird observers, and thereby to save costs, in regional forest biodiversity monitoring programs. The setting was the Pilliga forests of north-western New South Wales where a major biodiversity monitoring program is underway.
The aim of the project was to assess the effectiveness of an autonomous sound recording system (SongMeter 2+, Wildlife Acoustics, Inc. Massachusetts, USA) in recording the presence of forest bird species in comparison with the results of standard, on-ground bird surveys using experienced bird observers. Specifically, we wanted to know which species could be detected reliably, if they were present, using SongMeters. Systematic, fixed-time, variable-radius, point-counts of all birds seen and heard by two experienced observers were compared to the species identified from sound recordings made simultaneously at the same sites. Paired comparisons between the two methods were available for 136 ten-minute census periods across 36 sites.
SongMeters provide a number of important advantages
On a per-unit-time basis, the two survey methods agreed in their identification of bird species on approximately half of the occasions when common bird species were encountered. This level of agreement declined to about one-third for detections of uncommon species. Experienced observers recorded about 1.4 times more bird species per ten-minute census period during point-counts than in simultaneous call recordings, but about 1 in 6 species were recorded only by experienced observers in the field.
SongMeters can be programmed and set to record autonomously in the field over extended periods, thus potentially overcoming many of the limitations observed in per-unit-time comparisons. However, the collection of such voluminous amounts of data will require the development of an automated process for identifying bird species from digital recordings. Also, certain cryptic species, including raptors, may never be adequately sampled using sound recording devices.
SongMeters have the potential to match, or exceed, the numbers of bird species recorded by experienced bird observers during standard field surveys and in species monitoring programs. SongMeters provide a number of important advantages, including standardisation of survey procedures and the provision of an archived record of point-count data.
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