Oficialdegui, FJ & Serrano, D 2024. Variability of a consistent trait: The size of the white wing patch in European Stonechats (Saxicola rubicola rubicola). Ibis 166: 187-199.
"The wing patch was larger in males than in females for all age-classes, and first-year individuals exhibited smaller wing patches than older birds, particularly males. This trait also varied within the plumage-year at both population and individual level, with slight changes from the moulting period to the breeding season and a sharp decrease afterwards. In addition, patch size varied both between and within individuals across years." (abstract, p. 187)