Determining how phenotypic traits covary within individuals can offer information on the underlying functional interactions of complex phenotypes and the mechanisms that promote them. We investigated covariation of the white wing patch of the Eurasian Black-billed Magpie (Pica pica) with age, sex, feather wear, spleen size, parasite infection, and testis size to evaluate whether this trait is indicative of individual quality. The white wing area was larger in adults than in second-year individuals, in males and females with larger spleens and lower helminth parasite burdens, and in males with larger testes. In addition, feather wear scores were positively correlated with black melanized areas at the tips of feathers. Our results suggest that wing whiteness reflects age, immune capacity, and feather quality in both sexes and reproductive potential in males. Therefore, this character may play a role in sexual selection by signaling individual quality.