Evaluation of the “safe nesting zone” hypothesis across an urban gradient: a multi‐scale study

Abstract

Urban areas have been considered “safe zones” for nesting birds because of low abundance of predators, and consequently low predation pressure. We studied risk of artificial ground nest predation across an urban gradient at regional (100×100 km) and local scales (5×5 km, within town) in Finland, Italy, and Spain. Risk of nest predation differed between countries, being greatest in Spain (66%), intermediate in Finland (51%), and lowest in Italy (29%). At the regional scale, risk of nest predation in Finland was lower in small villages and in forest area than in more urbanized sites. In Spain, the risk of nest predation was lower in villages than in the other habitat types. No differences in nest predation risk among habitat types were observed in Italy. At the local level, the risk of nest predation in Finland was higher within the town than in the surrounding forest. In Spain, the risk of nest predation in the surrounding forest area was as high as in the most urbanized areas. No difference in nest predation risk was observed between study plots in Italy at the local level analysis. Our results indicate that nest predation in town centers and their residential areas is similar to or higher than in villages and forest areas refuting the safe nesting zone hypothesis. Risk of nest predation also differed between residential area types within towns. Moreover, the abundance of potential nest predators differed between countries. Magpies and crows were more abundant in Finland than in Italy and Spain, whereas cats, dogs and pedestrians were less abundant in Finland than in the other countries. In Finland, risk of nest predation increased with the abundance of magpies. In Italy and Spain, risk of nest predation increased with the number of pedestrians and in Italy also with the number of cats. In all countries, the risk of nest predation increased with the visibility of the nest. According to our results, urban areas cannot be seen as “safe nesting zones”. Actually, changes in nest predation pressure may cause changes in habitat selection patterns and affect bird community structure in urban environments.