Wind turbine impacts on wildlife are important issues for wind project acceptance.Different effects are associated to wind energy development: collision, when birds are killed habitat loss, when birds abandon the area because of a wind farm barrier effect, when migrating birds modify their flight paths to avoid a wind farm If the two first impacts are well known for the most part of the time, this is not the case of the barrier effect.As a consequence of going around obstacles, migrating birds spend more time flying, which increase the amount of energy they need to achieve their migration, which in turn can reduce their survival.In theory, the development of wind farms all along the migration routes may have an impact on migrating bird at a population level.However, how much the barrier effect is responsible for the decline of migrating birds is unknown.We present analysis on different species witch are representative from northern hemisphere avifauna and from different migration typology.Starting with those biological models we propose barrier effect impact quantification on bird populations and mitigation solutions combining industrials and environmental issues.Our presentation starts with a synthesis of what is known today in terms of flight energy costs, flight physiological adaptation, and migrating bird ecology.Examples are then used to : propose a methodology to quantify the barrier effects and their impacts on bird populations, present practical and operational solutions to reduce the impacts of wind farms on migrating birds.