GreenTracker| Flamingos in Spain apply natural make-up to the feathers for the express purpose of attracting mates. A new study by Juan Amat and colleagues, is the first to demonstrate that birds transfer the color pigments (carotenoids) from the secretions of their uropygial gland for beauty and cosmetic reasons. As you might imagine, the uropygial or preen gland is found near the base of the tail, in the majority of birds.
There us evidence that some bird species modify their colors using external sources, besides their own secreted pigments.
The seasonal variations in plumage color tied directly to the courtship activity of the flamingos.
They found that the plumage of flamingos was more colorful during periods in which the birds were displaying in groups and faded during the rest of the year. This fading occurred shortly after the birds started to breed. via Science Daily