BERGH LMJ VAN DEN, SPAANS AL & SWELM ND VAN (2002) Wind turbine lines no barrier for gulls an d terns flying to and from feeding areas during the breeding season. LIMOSA 75 (1): 25-32.

We studied the behaviour of gulls (mainly Herring Larus argentatus and Lesser Blackbacked Gulls L. graellsii) and Common Terns Sterna hirundo fIlying between breeding colonies and feeding areas at sea at two wind farms (Slag Dobbelsteen and Slufterdam, with lines of nine and thirteen turbines, respectively, each turbine with a tip height of 56.5 m) at the Maasvlakte (Port of Rotterdam), The Netherlands, during six days in July 2001 (Fig. 1) Birds were active during the whole day, with numbers of flights declining to almost zero sometime after sunset. During evenings around full moon gulls continued flights for a longer period after sunset than during dark evenings (Tab. 1) Flight altitude varied between less than 1 m to over 400 m (Tab . 2), but most birds flew at wind turbine height (Slag Dobbelsteen 62%, Slufterdam 92%). Birds approaching lines at turbine height did not react to turbines in a significant way (Tab 3) This behaviour differs strongly from that during the non-breeding season , when birds react strongly to turbines. The same difference holds for distribution and numbers of birds nesting in an area compared to roosting and feeding nonbreeding birds. The data suggest that during the breeding season birds are either less sensitive to disturbance by wind turbines or habituate sooner to these obstacles than outside this period

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