Small-scale spatial variation in the interactions between Prunus mahaleb and fruit-eating birds

We studied fleshy fruit consumption by birds on individual Prunus mahaleb trees in four plots in northwestern Spain. We found large variation among trees in the relative contribution of different bird species to fruit removal. This variation, which occurred on a scale of meters, was correlated with the distance from the tree to nests of Phoenicurus ochruros, a major fruit consumer, and with the kind of microhabitat surrounding each tree. In the four plots studied, trees located farther away from P. ochruros nests received relatively fewer visits by this species, and relatively more by Turdus merula and Sylvia atricapilla. These three main consumer species differed in the kinds of microhabitats (rocks, loose stones, bare or grassy soil, and woody vegetation) where they flew after visiting P. mahaleb, and thus they probably created different patterns of seedfall. This study adds to the evidence that environmental factors extrinsic to plants, and acting at different spatial scales, greatly influence the identity of the fruit consumers visiting individual trees. This influence undermines the chances that fruit traits become evolutionary modified so as to attract those consumers providing the "best" seed dispersal services to the plants.