Passive audio recording

Passive audio recordings can be long-term, pre-programmed to record during certain periods and over many days/weeks (i.e. SM4 recorders, Audiomoths or, Swift Bioacoustics recorders), or, over a shorter time frame (i.e. a Dictaphone during walk over survey).

Passive audio should be considered as supplementary under any one of the following circumstances:

• The presence of priority nocturnal species (e.g. nightjar, long-eared owl, nightingale);
• Specific species surveys are required to prove presence on site, particularly where densities may be low (e.g. nightingale, skylark, willow tit);
• To identify the extent nocturnal migration over a site;
• To identify the presence of nocturnal site usage of a particular aspect or habitat (i.e. foraging waders or wildfowl); or,
• Where difficult terrain prevents survey access to fully understand species composition on site (i.e. warblers in reed bed or dense scrub).

These circumstances should also be used to determine the location and duration of a recording session.

Audio recordings of rare and priority species should be stored for review at a later date and archived with county recorders/research organisations, and online, open-source bird call repositories (i.e. xeno-canto).

Data collected through passive monitoring techniques should be analysed by experienced surveyors, familiar with nocturnal vocalisations (as many diurnal species have different calls at night).

Passive recording for species specific surveys can only prove presence on site and does not confirm absence.