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Impacts on sea birds

The influence of offshore wind farms on birds can be summarised as follows:

  • Collision risk.
  • Short-term habitat loss during construction phase.
  • Long-term habitat loss due to disturbance from wind turbines installed and from ship traffic during maintenance.
  • Barriers to movement in migration routes.
  • Disconnection of ecological units.

The methodology proposed by Fox to support EIA of the effects on birds of offshore wind farms reveals the great complexity of the analysis. The relationships between offshore wind farms and bird impacts must be analysed by gathering information about avoidance responses, energetic consequences of habitats modification, avoidance flight and demographic sensitivity of key species.

Figure 2.2: Flow chart of hazards factors to birds by offshore developments.

Figure 2.2: Flow chart of hazards factors to birds by offshore developments. Boxes with solid frame indicate measurable effects. Boxes with double frame indicate processes that need to be modelled.

Collisions have the most direct effect on bird populations.

Collision rates for wintering waterfowls, gulls and passerines on coastal areas in Northwest Europe range from 0.01 to 1.2 birds/turbine. No significant population decline has been detected. Direct observations from Blyth Harbour, UK, have demonstrated that collisions with rotor blades are rare events in this wind farm located within a Site of Special Scientific Interest and Special Protection Area, under the Birds Directive.

In poor visibility conditions, large numbers of terrestrial birds could collide with offshore wind farms, attracted by their illumination. This occurs only on a few nights. Passerines are the group mainly involved in these collisions. One of the most useful mitigation measures to avoid this type of impact is to replace the continuous light with an intermittent one.

Information about bird mortality at offshore wind farms is very scarce for two reasons: the difficulty of detecting collisions and the difficulty in recovering dead birds at sea. Further investigations on this topic are needed to get reliable knowledge.

There is a lack of good data on migration routes and flight behaviour of many of the relevant marine birds' species. But this data is essential for assessing the potential impacts of collisions and barriers to movements. The large scale of proposed offshore wind farms together with the expected cumulative effects increase the need to fill in these gaps.

The degree of disturbance differs between different species. The disturbance may be determined by several factors such as availability to appropriate habitats, especially roosting and feeding areas, time of year, flock size and the layout of the wind farms.

Disturbances during construction are produced by ships and/or helicopter activities and noise generated by ramming piles. After that, in the operation stage, disturbances by boat traffic have an impact on birds.

The impacts of marine wind farms are higher on resident sea birds, coastal birds and migrant birds than those on onshore birds. The reasons for this higher impact at offshore developments is related to the larger height of marine wind turbines, the larger size of wind farms and the higher abundance of large bird species, which are more sensitive to disturbance.

The most important findings after seven years monitoring Horns Rev and Nysted wind farms indicate negligible effects on overall bird populations. The majority of bird species showed avoidance to the wind farms. Although there was considerable movement of birds around wind farms, however, between 71-86% of flocks avoided the wind farm between turbine rows. Changes in flying directions, for most of the species, were verified at 0.5 km from wind farms at night and at 1.5 km in the day. This avoidance represents an effective habitat loss, but the proportion of feeding area lost due to the presence of these two wind farms, in relation to the total feeding area, is relatively small and is considered of little biological importance. Avoidance behaviour reduces the collision with turbines. The displacement of birds because of wind farm installations makes the collision risk at the two installations low. The predicted collision rates of common eiders at Nysted were 0.02 %, which means 45 birds over a total of 235,000 passing each autumn in the area. Monitoring has also confirmed that water-birds (mainly eider) reduce their flight altitude, below rotor height, at the Nysted wind farm.

Avoidance observed in Nysted and Horns Rev affects flying, resting and foraging between turbines. New wind farm proposals in the same area have to be carefully analysed because they may cause important habitat loss for certain species.

The EIA on marine ecosystems must take into account the cumulative effects from all the wind farms in the surrounding area, including cable connections to the network on the mainland.

During the last several years, a lot of methodologies on collision risk models, baseline surveys both using ship and aerial techniques and post-construction monitoring have been developed. This data is needed to properly assess and predict the future impacts of proposed wind farms. Several sophisticated technologies such as radars, infra-red cameras, etc. have helped to gather a better understanding.

When there is not enough knowledge about specific species or taxonomic groups in unstudied habitats, the potential disturbance distances could be unknown. The most appropriate approach to define the disturbance distance may be to determine the bird numbers at different ranges of distances from wind farm, ensuring that all the affected area is covered in the study.

There is a common opinion on the need for more information about potential impacts of wind farms on birds. Further research is required on avian responses to wind farms, models to predict the future impacts of a new single wind farm installation and groups of wind farms on an area, the collection of information on bird movements to design the marine sanctuaries of birds, and data gathering standardisation methodologies.

Mitigation measures to onshore schemes are also applicable on offshore wind farms.

Ship collisions

Ship collisions with the turbines are one of the potential risks associated with offshore wind energy development. Colliding with a wind turbine foundation could damage or possibly destroy a ship.The potential danger to the environment is the spillage of oil or chemicals from the ship into the water.

Evaluation of several collision scenarios between three different types of turbine foundations (monopile, jacket and tripod) and different ship types (single and double hull tankers, bulk carriers and container ships) has been tested in several locations of the North Sea and Baltic Sea off Germany. The results have demonstrated two main results: The first is that monopile and jacket foundations are safer than tripod structures, and the second is related to the risk of collision which can be reduced, but not totally avoided.

There are several safety approaches applicable to avoid or minimise this potential risk:

  • Redundant navigation and control systems.
  • Prohibition on navigation to certain kind of ships.
  • Introduction of traffic management systems.
  • Wind farm monitoring.
  • Availability of tug boats for emergencies.
  • Crew training on this topic.
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