Birds

The North Sea is home to many different birds. Some of these birds, such as a number of seabirds and coastal birds, live here permanently. Seabirds spend most of their lives at sea and often only come ashore to breed. Coastal birds rest and breed on land and go out to sea to look for food. In addition to these permanent residents of the North Sea, many millions of birds migrate across the North Sea every year during the spring and autumn. In addition to the typical coastal birds and seabirds, large numbers of land birds (such as songbirds) also migrate along or across the North Sea on their way from breeding grounds to wintering grounds, and vice-versa. In broad terms, there are two main migration routes across the North Sea. An east-west route that the birds take from the mainland to the British Isles in the autumn. And a north-south route taken by large numbers of migratory birds which fly in the autumn from Scandinavia over the northern North Sea towards the English Channel or the south and south-west of Europe. The birds take these routes in the opposite direction in spring.

Non-seabirds in particular prefer to migrate when the conditions are favourable (when there is a tailwind, no precipitation and no closed cloud cover) over large sea areas. On favourable days, songbirds and waders often fly at altitudes of hundreds of metres, rising to more than two kilometres. When the conditions are not as favourable (for example when there is a headwind) the birds do not fly as high. Altitudes of approximately 100 m (the rotor height of a wind turbine) are not uncommon at these times.

Offshore wind farms may affect birds in different ways: there may be a loss of habitat, a barrier effect or death due to collision. In the event of a loss of habitat, the seabirds and/or coastal birds avoid the wind farm and so the habitat of the species is restricted (possibly temporarily as the birds, for example, may get used to the presence of the wind farm). A barrier effect means that birds are no longer able to fly or swim through or over the farm. In that case, flight distances will increase, causing the birds to spend extra time and energy. There is a risk of collision both for migratory birds flying at rotor height, for example because conditions are unfavourable, and for coastal birds and seabirds, such as seagulls, guillemots and cormorants, that live in the vicinity and go looking for food in the wind farm.

Because birds have a protected status, Wozep (the Offshore Wind Ecological Programme) is studying the possible impact on birds of the presence of offshore wind farms. This information may be used for, among other things, establishing or refining specific permit requirements in order to mitigate possible effects.

Use of current research results

The bird research helps to reduce the uncertainties relating to the impact of offshore wind farms on birds. This will result in more accurate environmental impact assessments  for the wind farms in the future. In addition, it will allow for more accurate calculations with the Framework for Assessing Ecological and Cumulative Effects (KEC) of the cumulative effects of wind farms on birds. The KEC quantitatively assesses the potential cumulative ecological effects of the wind farms in the southern North Sea at present, as well as of wind farms that are under construction or planned for the future. In addition, a better understanding of the effects will provide a firmer footing for permit requirements that will be included in the site decisions for the wind farms.  A permit requirement of this kind can relate to, for example, mitigation measures for migrating songbirds. To reduce the risk of collision at times of mass[1] nocturnal bird migration, a curtailment strategy has been included in the site decision in which the rotor blades may not turn faster than one revolution per minute between sunset and sunrise.

Ongoing Wozep research

A number of studies are currently in place involving the monitoring of various coastal bird species (including the Curlew, Sandwich Tern, Herring Gull and Lesser Black Backed Gull) with GPS tags. That generates an enormous amount of information about the flight movements and behaviour (including avoidance) of these birds. Advanced radar systems are also being used at the Luchterduinen and Borssele wind farms to map out flight movements (within the range of the radar). These data are used to improve the collision-risk model, which predicts the number of collision victims. In addition, Wozep is working to improve the availability of a large proportion of the international bird data. All these data will be used as input to validate and improve the assumptions underlying the collision, habitat use and population models, which are in turn used to establish a clearer understanding of the impact of offshore wind farms on birds.

List with reports on completed studies

[1] mass bird migration: a bird density of 500 birds at rotor height per kilometre per hour