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Teil C - Annex 
5 Bats 
See Table 5.1 : Survey of bat migration activity in the offshore area. 
Process instruction for survey of bat migration activity in the offshore area of the Baltic 
Sea. 
Scope of application 
The process instruction should be seen as a guideline for the qualitative survey of bat occur 
rence and for the relative estimate of bat activity in the assessment area during bat migration 
times. In the Baltic Sea region, bat migration is expected, depending on the species, in the 
period from mid-April to mid-June and mid-August to end of October (e. g. Ahlén 1997, See- 
bens et al. 2013). 
So far, the knowledge base for correct offshore monitoring of bats is limited. This process in 
struction is a first step towards standardised survey. It will be evaluated and reviewed with 
further development of the StUK. 
The survey of bat fauna is carried out in the style of the night-time call survey of migratory 
birds (of. Table 3.2.2) and comprises the acoustic recording of écholocation calls. The proba 
bility of recording these calls depends on the species-specific call “volume” and on the tech 
nical characteristics of the used acoustic detectors (frequency-dependent sensitivity, direc 
tional characteristic) (e. g. Adams et al. 2012). Most species or species groups can be identified 
on the basis of their call characteristics (species spectrum). The number of bat call sequences 
provides information regarding their relative activity. 
Equipment for recording/analysis of bat calls 
The survey system presented below follows the Avisoft system. If other survey systems are 
used in the context of offshore surveys, it must be ensured that they comply with the minimum 
requirements and equipment standards presented here. 
The survey system must fulfil the following minimum requirements. It must be noted that only 
detector systems with a high sensitivity range of 16-25 kHz are permissible: 
Bat detection system: 
• Bat call recording per second 
• Real time recording 
• Minimum sampling rate 300 kHz 
• External microphone port 
• Calibration possible 
• Option for bat call filter 
Microphones: 
• External ultrasound microphones (e. g. Knowles FG Electret Ultrasound or CM16/ CMPA) 
• Shielded microphone cable with shielded 5-pin XLR connector 
• Waterproof microphone cover (e. g. plastic tube) 
• Signal generator for testing functionality and for regular calibration 
• Microphone heating (Note: microphone heating has the advantage of reducing condensa 
tion and thus salinisation of the microphone)