White cheeks are more titillating

Male blue tits with white cheeks are healthier and more likely to mate with higher quality partners than their counterparts with duller cheek feathers. Having purer white cheeks also indicates that a blue tit was better able to overcome an infection with parasites during the previous year.

Click here to read the rest of the article: White cheeks are more titillating: New bird study shows that the health and attractiveness of male blue tits is linked to the whiteness of their cheek feathers — ScienceDaily