A Wageningen Marine Research study shows that razorbills and guillemots on the North Sea avoid wind parks in their flight path. The study uses a new statistical method to determine the effect of wind parks on the spatial distribution of seabirds.
The rapid growth of offshore wind parks in the North Sea necessitates a better understanding of the impact of wind turbines on marine species. The classical method was for researchers to conduct a census of the bird population in the wind park using aeroplanes and ships and subsequently compare the results with those obtained in nearby similar areas. 'We would see the differences, which are always present when two areas are compared, but we could never be certain that the differences were caused by the presence of wind turbines', says researcher Mardik Leopold.
The new method has researchers conduct eight censuses from aeroplanes at a considerable altitude, which enables them to determine the population density of the birds in a 25-kilometre radius around the wind park using advanced image processing methods. A new statistical method is then used to determine the size and intensity of the disturbance, where the surrounding area is used as a control area.
Lower density of guillemots and razorbills
The researchers discovered that the density of guillemots (Uria aalge) and razorbills (Alca torda) was much lower in the wind parks than in the surrounding area. Their densities dropped by approximately one and one-and-a-half birds per square kilometre under the influence of the wind park. These two bird species are highly common in the North Sea region. Leopold: 'We were also able to determine until what distance from the park the seabirds are affected by the park, which is to say: have lower population densities. For guillemots, that range is no less than 10 kilometres.'
Seabirds' habitat loss
Thus, researchers have mapped the seabirds' habitat loss for the first time, within and outside of a wind park in the Dutch North Sea. Leopold: 'This study does not concern fatalities due to collisions with wind turbines, but habitat loss, which is potentially much more detrimental to seabirds than fatalities that occur through collisions. Habitat loss is a permanent situation; the seabirds' living space is reduced, while a new generation can replace birds that perish through collisions.'
According to Leopold, the method developed by Wageningen Marine Research should be elevated to the standard for measuring the impact of wind parks on seabirds. But is habitat loss problematic if the birds fly around the offshore parks? Leopold: 'The sea available to these birds becomes smaller, their living environment shrinks, but we do not know whether that causes a reduction in their population. That calls for an answer to the question of what precisely the limiting factor is for the razorbill and guillemot population on the North Sea. Their living environment is an option, but it could also be the availability of food or the number of breeding spots. The construction of offshore wind parks appears to be no issue for these species if the latter is the case, but further investigation is needed.
This study was conducted around the Gemini Offshore Wind Park, some 55 kilometres north of Schiermonnikoog, a co-financier of the project. The Agri&Food Top Sector also funded the project.
