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12.5 • Results and discussions121 12FINO3, located 136 km to the northeast of FINO1and west of the island of Sylt: At FINO3, high butunexceptional migration intensity was recordedby an identical horizontal radar. Birds passingFINO3, however, still encountered fairly goodweather conditions. They flew at higher altitudesand were headed towards the west and southwest(. Fig. 12.13), as expected for autumn migration.Such comparisons show that bird migration andconstraining or supporting weather conditions candiffer considerably between different sites within theGerman Bight at any one time.Apart from providing such highly soughtafterinsights into behavioural responses relatingto weather, horizontal radar also supplements thepicture outlined by vertical radar: Because of itsmounting position, the vertical radar detects birdsonly within a limited section outside of the windfarm.In contrast, horizontal radar scans nearly fullcircle around FINO1 every 2.5 seconds, thus allowingcoverage of parts of the windfarm as well.Differences consequently become visible betweenthe figures illustrating the nights between31 October and 2 November 2010. According tovertical radar, the night of 31 October to 1 November2010 showed moderate migration intensitycompared with the ensuing mass-collision night(. Fig. 12.12), whereas horizontal radar showedroughly equal intensities (. Fig. 12.14). This is inline with data obtained with the pencil beam radar,which confirmed especially high migration rateswithin the windfarm reflecting overall high migrationintensity (see below).To be able to tell the whole story, data was gatheredcontinuously using several optical systems.Video and thermal imaging cameras at FINO1 recordedpeak-storage images (▶ Information box Remotesensing technologies), providing a useful tool foranalysing the behavioural reactions of specific speciesto a windfarm in daylight conditions. At night,a video camera aided by strong infrared illuminatorsand two thermal imaging cameras observedthe rotor-swept zone of the turbine closest to thetransformer station, albeit still from a distance of250 m. Over three years of data acquisition, the twosystems recorded hundreds of birds flying throughor near the blades (. Fig. 12.15), though no directcollisions were observed. The weakness of optical..Fig. 12.13 Direction of recorded bird tracks at FINO1 (left)and FINO3 (right) during the night of 1 to 2 November 2010for two elevation levels (see vertical axis) measured by parabolicantenna. n‐tracks are given in each case.systems is their limited range in bad weather: Withmore water droplets in the air, visibility and hencethe ability to detect birds is reduced. Nevertheless,all optical systems showed various bird signaturesin the vicinity of alpha ventus during the night of1 to 2 November 2010, but visibility was too low toobserve birds directly in the rotor area.Every detection method has its advantages anddisadvantages. The lesson learnt is the need for thoroughanalysis comprising and combining differentremote sensing techniques at various spatial scales.12.5.2 ‘Ground-proofing’ throughautomatic detection of speciesspecificbird callsMany bird species utter calls during migration (e. g.Farnsworth 2005). Registered by a sensitive microphoneand processed by specially developed softwarecalled AROMA (Automatic Recording of MigratingAves), the system in use on FINO1 autonomouslyrecognises bird calls by their characteristic narrowsound spectrum and filters out most wind, rain andwave noise. Bird calls are stored as audio files (Hill& Hüppop 2008) and recordings are subsequentlymatched to species by qualified staff. Given the re-