Aims: To study the habitat features affecting the risk of nest predation of birds nesting on the ground or the shrub layer in pyrenean oakwood forests of central Spain, and the variation across different forest areas.
Location: Four pyrenean oak Quercus pyrenaica forests in the Sistema Central (Madrid, Spain). Methods: Estimation of predation rates of artificial wicker nests baited with two quail eggs in four oakwood sites spanning over 700 km2. Predation rates of individual nests were related, by means of generalized logistic regression models, to different forest locations, habitat features in nest surroundings, and shrub species characteristics where artificial nests were placed.
Results: Variation in predation pressure was explainable to a low extent by predictor variables (less than 33 % of the original deviance). The most remarkable differences in predation pressure were attributable to forest location. Predation risk of artificial nests placed on shrubs decreased with the development of the shrub layer around the nests, and increased in places with a high density of young trees and a large cover of the herbaceous layer. Shrub characteristics related to the probable accessibility of nests did not influence predation risk.
Conclusions: This study demonstrates a small effect of habitat structure of the nest surroundings on the predation risk of nests placed on the ground or shrubs within pyrenean oakwood areas. A trend towards a lower predation pressure was observed in areas with less immature trees and a large shrub cover 10 m around the shrub nests. However, forest tracts where the nests were placed largely determined the predation risk they suffered to an extent not directly associated with habitat structure.
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