Since the early 1990s, marine wind farms have become a reality, with at least 13 000 offshore wind turbines currently proposed in European waters. There are public concerns that these man-made structures will have a significant negative impact on the many bird populations migrating and wintering at sea. We assess the degree of usefulness and the limitations of different remote technologies for studying bird behaviour in relation to bird-turbine collisions at offshore wind farms. Radar is one of the more powerful tools available to describe the movement of birds in three-dimensional space. Although radar cannot measure bird-turbine collisions directly, it offers the opportunity to quantify input data for collision models. Thermal Animal Detection System (TADS) is an infra red-based technology developed as a means of gathering highly specific information about actual collision rates, and also for parameterizing predictive collision models. TADS can provide information on avoidance behaviour of birds in close proximity to turbine rotor-blades, flock size and flight altitude. This review also assesses the potential of other (some as yet undeveloped) techniques for collecting information on bird flight and behaviour, both pre-and post-construction of the offshore wind farms. These include the use of ordinary video surveillance equipment, microphone systems, laser range finder, ceilometers and pressure sensors. BIRDS AND OFFSHORE WIND FARMSMigratory bird species enjoy a high public profile and are protected by international and national legislation designed to protect shared natural resources. Hence, migrant birds figure prominently in the environmental impact assessment (EIA) process associated with most wind farm development projects. The coastal and offshore waters of Europe are of global importance for several species of resident and migratory birds. The hazards posed to birds by the construction of offshore wind farms can be summarized under three broad headings: (1) Displacement and flight avoidance responses (birds are displaced from an ideal feeding distribution by the presence of turbines, or avoid flying near to them on migration); (2) Habitat loss/modification (physical habitat loss under foundations, or the creation of novel feeding and resting opportunities that actively attract birds to the turbines); and (3) Collision risk (the probabilities of individuals of different species being struck by turbines).Of these, collision risk will have the most direct impact at the population level, because it elevates the normal mortality rate of species (Johnson et al. 2002). This review will mainly focus on the risk of collisions. However, this does not imply that the other effects are trivial, especially when the cumulative effects of, for example, habitat loss are considered in the light of the construction of many offshore wind farms along the length of a migratory bird species' corridor . DEFINING THE ROLE OF REMOTE TECHNOLOGIESTo support an adequate assessment of the risk presented by each hazard, and subsequen...

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The use of radar to detect ships and aircraft became a key part of Britain's defence in the early part of the Second World War, but not all echoes were those of operational targets. David Lack, of the Army Operational Research Group, showed that many unexplained echoes came from flying birds, despite critics at the time. Careful observation combined with experiments provided observers with means of differentiating birds from boats and aircraft. Lack went on to use his wartime experience to launch the science of radar ornithology during the 1950s, which formed the basis of a development that continues to the present day with a range of more sophisticated radar equipment.