Nest site selection: A trade-off between concealment and view of the surroundings?

For most birds, nest predation is the main cause of reproductive failure. Many species reduce predation by hiding their nests in vegetation. However, it is unclear whether they maximize cover around nests. Individuals may benefit also by keeping potential predators, food, and conspecifics in view, and selection of nest site may be a trade-off between concealment and visibility. We examined this idea in the Song Thrush Turdus philomelos, which builds cup-shaped nests in trees. For artificial nests, the risk of predation decreased when nests were more concealed within individual trees. However, Song Thrushes did not maximize concealment of nests within trees but selected intermediate concealment from the range of concealment available. The proportion of destroyed natural nests was not related to degree of nest concealment. Song Thrushes also selected patches of intermediate tree density, but tree density did not influence predation rate of artificial nests. These results are consistent with the trade-off hypothesis, which deserves more attention in future studies of nest site selection.