Factors affecting road mortality in birds

Abstract

Several hundred million birds are killed on an annual basis worldwide due to collisions with vehicles.While this is well documented, less data exists on specific factors affecting thenumber of roadkills. I examined roadkill patterns while driving a car during a 44-month period (617 days, twice daily) along a 25 kmstretch of road in themiddle ofNorway. In total, 121 roadkills were detected during that period. I used information on bodymass, speed limit, vegetation in the vicinity, flight distance, abundance of birds in the surrounding environment and number of birds sitting on the road in order to elucidate their effects on the number of roadkills and susceptibility to become a roadkill for 30 different bird species/ groups of species. Roadkill numbers were highest in summer, and at certain parts of the road the mortality rate was much higher than in others. Heavier birds flew away from the approaching car at a longer distance than smaller birds, but they still had a relatively high mortality rate. Birds known to search for food on roads were more likely than other birds to become roadkill. Birds observed on the road explained a significant amount of the variation in roadkills between the species, in contrast to the abundance of birds in the surroundings. Fewer birds than expected were found where the speed limit was highest, and roadkilled birds were visible for a longer period when their body mass was higher.