WINKELMAN JE (1985) Bird impact by middle-sized wind turbines - on flight behaviour, victims, and disturbance. LIMOSA 58 (3): 117-121.

In the autumn and winter of 1983/84, the possible danger of medium-sized wind turbines (tower height 10-30 m, rotor diameter 7-25 m, power 50-300 kW) to birds was studied at six sites in the coastal area (fig. 1, tab. 1). Main points studied were flight behaviour of birds approaching turbines within 200-300 m distance in daylight and fine weather (good visibility), number of birds killed at night, and possible loss of breeding and feeding habitat around present sites of turbines. During just over 341 hours of observation, 87000 birds in 6200 flocks were recorded. Only 561 flocks (719%, on average 13%, of migrating flocks; 4-6%, on average 5%, or local flights) showed a change in flight behaviour that could be attributed to the turbines. No collisions with the turbines were seen. Among the studied factors, type of bird movement (migration or local flights), action of turbine (operating or not), site, bird species, time of day, flight height, distance to the turbine, wind force, and wind direction influenced the extent of hindrance. Some results were suggestive of habituation of local birds to wind turbines. Flock size did not seem to influence the response. Most responses (97% diurnal migrants, 100% local flights) were a temporary evasion of the entire turbine, 3% (diurnal migrants) came within reach of the rotor. Outside the rotor, a possible panic reaction was noted in 1% of the flocks. The majority (84-99%) of the flocks avoided the obstacles by shifting their flight paths to the side (most oftcn by 16-45?), mainly staying at the same height. Within thc observed field, 27% of the diurnal migrants returned to the original track after reaction, none of the local birds. Of the 50 groups seen within reach of the rotor, 38% showed a reaction. Observations were not always equal for the entire field of observation; there was also a parallax problem. No dead birds were found in the vicinity (~ 50 m) of the turbines. This confirms the scarce data from the literature, but is difficult to interpret because of lack of data on removal of killed birds by scavengers, and lack of data on migration extent at low altitudes during the study period. Nearly all present sites of turbines are situated near other interfering elements and have a low bird life, so it can be presumed that the effect of these turbines on breeding and feeding habitat of birds has been negligible. The results show that the chance of collisions of birds with medium-sized turbines in daylight and in weather with good visibility is almost zero. At present sites, the disturbing effect of such turbines hardly interferes with feeding and breeding birds, if at all. The results do not indicate the danger of collisions at night or in daylight during weather with poor visibility, the hindrance caused by other types of turbines (particularly large ones), by turbines at sites in the open field and by large groups of wind turbines (e.g. wind parks), and the risk at sites other than those studied

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