Variation in the Wing Morphology of Western Sandpipers (calidris Mauri) in Relation to Sex, Age Class, and Annual Cycle

—We analyzed diff erences in wing morphology between sexes and among age classes of Western Sandpipers (Calidris mauri) to assess possible relationships with diff erential migration, acrobatic aerial displays, and potential vulnerability to predation, using size-constrained component analysis. Data on wing morphology of all four sex and age classes were available from birds spending the nonbreeding season in northwestern Mexico, and data on females were available from throughout the annual cycle. During the nonbreeding season, females had longer and more pointed wings than males. Within each sex, adults had longer and more pointed wings than immature birds. Throughout the annual cycle, adult females tended to have longer and more pointed wings than immature females. The longer and more pointed wings of females are consistent with selection on fl ight effi ciency for longer migration distances. The shorter and rounder wings of males are consistent with stronger selection for agility in fl ight during acrobatic aerial displays, but also with weaker selection for fl ight effi ciency because of shorter migration distances. The rounder wings of immature birds are most consistent with stronger selection for take-off performance as an antipredator adaptation, at a cost of lower fl ight effi ciency during long-distance migratory fl ight. Considering intraspecifi c sex and age class diff erences in wing morphology of species with diff erential migration complements interspecifi c comparisons assessing the relative importance of selective agents acting on this character. Received 8 May 2006, accepted 14 September 2006.