Influence of roads on bird nest predation: An experimental study in the Iberian Peninsula

Roads play an increasingly important role on the biology of wild animals living their natural surroundings, especially during the breeding season. The present work examines predation on artificial nests with respect to roadsides and the distance of such nests distance from roads in a woodland area in Western-Central Spain. Roads were classified according to traffic density, and field work was carried on from April to July in 2004 and 2005. A total of 720 nests were placed and 471 (65.4%) were disturbed by predators during the study. Nest fate was associated with the type of road (P < 0.001) and vegetation cover (P = 0.001). Such disturbances were greater (P = 0.02) at nests placed farther away (>25 m) from roads with high traffic density than on those located close to roadsides. Roads with a medium or low traffic density had a higher incidence of nest predation (P = 0.012 and 0.025, respectively) than nests distant from them. We conclude that predators do not use roads with high traffic density as travel corridors, and nor do they concentrate their foraging activities along them. Roads with a medium and low volume of traffic offer a greater probability of collisions with wild animals, and hence predators often use this type of roads to scavenge their food. We caution investigators to take into account the distances of nests to different types of edge when attempting to evaluate avian nesting success.