Nectar robbing, especially by birds, can damage the reproductive parts of a flower and thus diminish the fitness of a plant. In this case, the effect of robbery on a plant is direct. A good example of an indirect effect is the change in the behaviour of a legitimate pollinator, which either increases or decreases the fitness of a plant. There are both primary and secondary nectar robbers. Secondary robbers are those that take advantage of the holes made by primary robbers. While most flies and bees are secondary robbers, some species, such as "Bombylius major", act as primary robbers.