By over the visibility of the insects to reduce competition from the flowers of the same type, so. Bird flower pollen is distributed will be red to differentiate other types of flowers and different from most.
It is beyond the ability of insect vision. To reduce competition from flower to flower, so that the birds of the same species as the pollen is red to a distinct and different from most other flowers.
By the above vision of insects. In order to reduce competition from the flower of the same kind. So, flowers with a bird as spread pollen will have red to distinguish from other types of flowers As much as possible.