Bright beaks get the bird
Female birds find males with the brightest beaks the most attractive for good reason: these are also the healthiest birds.
Darwin would have been fascinated by these results. He suspected that traits influenced through Sexual Selection could simply be down to the whim of the selecting sex, and did not necessarily reflect factors that were advantageous in other ways. Wallace disagreed. These results lend support to Wallace's view, although Darwin's may well be correct in other cases.