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. This is according to Elisa Pérez Badás of the Museo Nacional de Ciencias Naturales in Spain. She is lead author of a study published in Springer’s journal The Science of Nature.