The fast development of wind power production into marine areas has caused great public concerns for the possible lethal effects on waterbirds. The present radar study documents a substantial avoidance response by migrating waterbirds to a large offshore wind farm. A larger proportion of the birds fly between the turbines at night compared to day time, but counteract this higher risk of colliding with the turbines in the dark by keeping a longer stance to individual turbines. Overall, less than 1% of the ducks and geese fly close enough to the turbines to be at any risk of collision.
In a new NERI radar study, the response of migratory waterbirds were investigated, when they approached an offshore wind farm. The study shows that eider ducks and geese are capable of discerning the rotating blades of the turbines in the Nysted Offshore Wind Farm, and that the majority of birds avoids to fly in between the turbines, where they are at risk of colliding with the structures. Just under 9% of the bird flocks, which passes the area, enters the wind farm area. The rest deflects laterally. The response pattern varies during the daily 24-hour period. Birds avoid the wind farm area to a larger extent during the day, when only 4.5% of the flocks crosses the wind farm area, in contrast to 13.8% in the dark.
The scientists count and identify migrating birds to species, using telescope.
The analyses also show that birds remain at a greater distance to the turbines during the night, while flying inside the wind farm. Thus, these birds reduce their collision risk. In total, less than 1% of the waterbirds migrated close enough to the turbines to be at any risk of colliding.
The results show that it is important to include the deflection of birds in order to avoid overestimating the collision risk. However, the scientists stress that the study is only supported by data compiled during the first year of electricity generation in the area. Frequent boat activity due to maintenance could have affected the flight trajectories of the birds. In addition, waterbird migration in the area is dominated by eider ducks and geese. Other seabirds may respond differently to offshore wind farms, and this ought to be studied.
A radar mounted on top of the observation tower follows the bird migation, which is transferred to a monitor inside the tower.
A part of the monitor is inserted on the picture. The green lines show the flight trajectories of birds.
The studies at Nysted continue in 2005. The aim is to compile more data on flight behaviour at an offshore wind farm and to investigate whether birds respond differently over time, e.g. as a result of habituation to the turbines.
Further information: Ph.D. student Mark Desholm, tel. +45 8920 1728, mde@dmu.dk or senior advisor Johnny Kahlert, tel. +45 8920 1507, jok@dmu.dk
Paper:
Mark Desholm & Johnny Kahlert: Avian collision risk at an offshore wind farm. Biology Letters 2005
Bron : National Environmental Research Institute (Denmark)