The Relationship between Wing Shape and Differential Migration in the Dark-Eyed Junco

Abstract

ABSTRACr.-We quantified wing shape in migrant and wintering Dark-eyed Juncos (Junco hyemalis) from southwestern Pennsylvania to assess the relationship between wing shape and differential migration (with respect to distance) among age/sex classes. There were significant differences in wing length and primary distances (distances from the wing tip to the tip of each of the nine primaries) among age/sex classes. Adult juncos had longer wings, larger proximal and distal primary distances, and a wing tip shifted proximally relative to immatures. Males had longer wings and larger proximal primary distances than females, but the sexes did not differ in distal primary distances or wing-tip placement. Wing-shape differences between males and females persisted even after accounting for differences in body mass between the sexes. With few exceptions, wing shape was not correlated with body mass within age/sex classes. The traits usually associated with a pointed wing (the wing shape generally considered adaptive for longer migrations) were really two independent dimensions of wing-shape variation in juncos that did not covary among age/sex classes. Overall, our results are inconsistent with the hypothesis that wing pointedness covaries positively with distance migrated in juncos. Received 14 April 1989, accepted 21 February 1990.