Bullfinches and ash trees : Assessing the role of plant chemicals in controlling damage by herbivores.

Wild bullfinches (Pyrrhula pyrrhula) feed heavily on the seeds of ash trees (Fraxinus excelsior). Field and laboratory studies show that individual trees with high levels of fat and low levels of phenolic chemicals in their seeds are especially liable to predation. This paper discusses (1) the complexity of effects that need to be examined in order to identify the role of secondary chemicals in determining herbivore preferences, and (2) the consequences of seed predation for the dispersal of seeds. Because of bullfinches' habits, and the many factors influencing seed dispersal and germination, it is not clear whether the birds' activities are necessarily damaging. This study emphasises the value of understanding the whole ecology of both plants and herbivores in order to interpret their interactions.