The study evaluates the impact onshore windmills can have on birds. It is generally assumed that power lines have more affect on birds than windmills do. However, birds do hit power lines and they collide with windmills even more. This research focused on two energy wind plants in the Straits of Gibraltar. The goals of the research were to find the effects of the facilities on bird behavior/habitat use, potential factors that could lead birds to the turbines, and mitigation measures.
Bird density is the likely reason for blade collision. Density increases the amount of birds in the area making it more likely for a bird to fly closer to a turbine. Bird density varies with the season and the season can have an impact as well. In the winter, the air currents are slower. Slower vertical air currents can affect Griffin vultures, which require strong vertical air currents to gain height. The most sensible approach would be to shutdown the small number of turbines that cause the most deaths, but only wind speeds that are the biggest risk.