Plumage dichromatism, wing–mass relationships and assessing the accuracy of field sexing techniques in breeding Semipalmated Plovers

Semipalmated Plovers Charadrius semipalmatus have a pattern of mixed sexual size dimorphism. Here we show that Semipalmated Plovers also have strong plumage dimorphism. Males are blacker overall, with fewer brown feathers in the crown and breast band and a shorter white supercilium than females. Males also have significantly more orange on the bill than females. Males have lower wing loading due to longer wings as a proportion of body mass, which probably provides benefits during display flights used for mate attraction. A discriminant function analysis using wing length, length of the supercilium and the number of brown feathers in the breast band correctly identified 91% (n = 106) of males, and 88% (n = 140) of females. Identifying the sexes of 17 individuals using the DFA and molecular techniques lead to 76% concordance (four mismatches). Plumage dimorphism is linked to territorial and courtship displays of males and is present primarily in breeding individuals. More efficient wing loading in males may have additional implications for sex-specific strategies of migration (e.g., time or energy minimization strategies). Use of geolocator data or behavioural observations during migration may help to test whether better wing loading in males has any benefits beyond the breeding season.