Vegetation structure governs nest predation in three types of conifer forest habitats

The primary hazard for open-cup nesting birds is nest predation. Vegetation structure and coverage may affect nest predation through various mechanisms such as the ability of a predator to locate the nests, which may vary between breeding habitats. We examined the association between vegetation structure and nest predation in three different types of pine plantations using artificial nests of the Sardinian warbler, Sylvia melanocephala, which were located 30 cm above ground in low bushes. We also assessed the relationship between bird abundance and nest predation in each type of forest. Finally, we identified predators through their bite marks on 3D-printed plaster eggs that were placed in the nests. The percentage of nests predated in pine forests with high understory coverage was significantly higher than in pine forests with only sparse understory. We also found that the nest predation rate positively correlated with total bird abundance and the abundance of S. melanocephala. The species of nest predators varied between different forest types, although rodents and birds were the most and second-most abundant predators, respectively, in each forest type. These results show that patches with only sparse understory vegetation within the forests generate nesting sites for birds with less risk of predation. But because bird abundance in this habitat type was relatively low, the net effect of preserving such habitat on the number of hatched birds should be further studied.