2000

The significance of mortality from collision with power lines for several species of birds has been evaluated by collision rates i.e., number of birds hitting a power line/number of birds crossing a power line. We estimated mortality from power line collisions for a wintering population of common cranes (Grus grus) and a resident population of great bustards (Otis tarda)in 2 study areas in Spain during 1992-1995. We estimated collision

rates at 3.93 x 10 -5 for common cranes and at 6.34 x 10-3 for great bustards. Risk exposure (i.e., power line crossings per unit of time) for common cranes was 714 times greater than for great bustards. Therefore, despite a high collision rate, minimum annual collision mortality for great bustards, present the whole year, was less than for common cranes, present only 4 months-1.58 and 2.36/km/year, respectively. Collision rate, which defines the chance of collision for a certain bird species, should be combined with
risk exposure and population size to evaluate the impact of collision mortality on bird populations.