Color mimicry of empty seeds influences the probability of predation by birds

Seeds are under strong pressure from seed predators. Therefore any physical seed trait increasing the chances of the seed’s survival should undergo positive selection. Seed color polymorphism, varying from pale to dark seeds, occurs in Scots pine (Pinus sylvestris), a keystone species of coniferous forests in Eurasia. This phenomenon can be explained by the production of large quantities of empty, always pale colored, seeds, with the opportunity for mimicry of these worthless seeds to avoid predation. Here, we investigated how the color of empty seeds may influence the foraging choices of the most common visual seed predator in temperate forests, the Chaffinch (Fringilla coelebs). We show, from field experiments, that different colored seed had different probabilities of predation by the chaffinch, and that predation was highest for dark seeds and lowest for pale empty seeds. Thus, the occurrence of empty seeds might benefit full seeds which mimic their coloration, even for those which are highly visible on the ground. In conclusion, the study demonstrated that mimicry by seeds of the color of the ground did not improve their survival but the production of pale full seeds resembling empty seeds did. This contradicts previous results and indicates that color polymorphism may reduce the predation rate by birds.