Time-triggered camera traps versus line transects - advantages and limitations of multi-method studies for bird surveys

摘要

Capsule: Time-triggered camera traps and line transects were compared in order to identify advantages and limitations of multi-method studies for bird surveys. Aims: To test whether, compared to traditional line transects, the use of time-triggered cameras with a short trigger interval of 20 s is an effective method for monitoring farmland birds, and to provide a detailed description of this monitoring method. Methods: We set up camera traps in flower strips and field margins in the county of Rotenburg, Germany, during winter (2012/13, 2013/14), summer (2013) and autumn (2013). In order to assess the results of camera traps, we conducted a comparative study by using line transects at the same study sites. Results: In total, we observed 20 bird species by camera trapping and 20 species by line transects but only 14 of these species were observed with both methods. Combining both methods leads to a higher number of 26 species. In flower strips, however, significantly more species were recorded by line transects than by camera traps. On the other hand, in field margins, line transects and camera traps contributed equally, indicating the advantage of combining the methods. Conclusions: The combination of camera traps and line transects is recommended for more reliable recording of bird communities. This combination was particularly beneficial in study sites with low bird densities and bird activity, such as field margins. However, in order to achieve reliable bird detections using time-triggered camera traps, a short interval between the pictures is needed. The limiting factor of time-triggered camera traps is the time-consuming viewing of the recorded images. Nevertheless, the benefit is that it can be conducted independently of time and space and it is weather- and researcher-independent. Moreover, camera traps allow multi-hour observations and necessary fieldwork time is short.