Environmental Impact Assessments (EIA) conducted during pre-construction phase of offshore wind farms clearly identified interactions between turbines and marine wildlife, especially seabirds, as a concern requiring further investigation. Mortality associated with collision could lead to negative impacts on seabird populations, and needs to be assessed on a case-by-case basis. Within environmental impact assessments, the Collision Vulnerability Index is frequently used to assess collision risk, and is based on several vulnerability factors among which flight height is the most critical. We therefore conducted a comprehensive literature review possible for the 82 species, including breeding and migrating birds, focusing on flight height and three others collision risk factors. We calculated an Uncertainty Level associated with flight height to take into account its reliability when calculating the Collision Vulnerability index. For approx. 20 species, the available information is satisfactory to assess flight heights. However, we identified 60 species for which further data collection is necessary to reduce uncertainty about vulnerability to wind turbine collisions, and identified existing GPS data which may facilitate further work. Within X-ROTOR, collision risk factors will be coupled with habitat use and conservation status into the Collision Vulnerability Index. This index will be applied to seabird distribution data to aid identification of suitable areas for the development of the X-ROTOR turbines.