Automatic radar and acoustic systems to monitor bird migration and behaviour at offshore windfarms

Alexander Schubert 1, Jorg Welcker1, Ross McGregor2, Thilo Liesenjohann1, Georg Nehls1
1BioConsult SH GmbH & Co. KG, 25813 Husum, Germany, 2HiDef Aerial Surveying, Cleator Moor, Cumbria, UK


Offshore wind farms may affect bird migration through collisions and barrier effects. To evaluate the potential impact, data on migration intensity, flight altitudes and direction as well as species composition was collected before, during and after construction of multiple windfarms in the German EEZ. Though this is usually done by ship-based surveys involving marine radar systems and human observers, new investigation methods include automated radar stations and digital acoustic sampling on offshore substructures.
These systems monitor bird migration continuously and can either be operated remotely from an onshore office or store data locally that can be retrieved at infrequent intervals.


Customized microphone boxes with high sensitive microphones and horizontal/vertical radar systems are installed on offshore structures such as met masts, hotel platforms or sub structures. Positioning is chosen according to the main migration routes and thus might vary between spring and autumn migration. Data is either stored offshore and hard drives are exchanged during standard maintenance works or send online to the onshore offices. Individually programmed software allows species identification, and annylsis of flight path and flight height if individual birds or flocks.


The daily and seasonal presence of birds showed a pronounced seasonality, indicating high migration intensities during the spring and autumn migration periods. Nights with very high numbers of birds detected in the lower flight altitudes of less than 200 m occurred rarely, but regularly during the migration periods. These nights were characterised by low visibility, onset of precipitation and adverse winds.


With limited man-power and minimal access to wind farms, using automated stations is cost-effective and reliable. For industrial and public clients, we successfully collected data at several wind farms and could provide thoroughly valuable findings on bird migration in the German Bight region. From these results possible impacts of wind farms on bird migration could be estimated.


Automated data sampling is a cost effective way to sample behavioural data of birds passing by or through windfarms, allowing to deliver reliable and reproducalbe einvironmental impact assessments.