Researchers have found that a rare yellow-faced Egyptian vulture eats sheep, goat and cow dung in order to keep its complexion. Apparently the bird's body does not produce carotenoids.
Carotenoids not only make carrots orange but they also give creatures the pigments they need for skin color. Researchers believe the yellower the face, the more it shows that the bird is immune to diseases cow dung could cause.
Researchers also believe that yellowness makes these vultures more attractive to potential mates and shows which vultures are stronger than others.