Variation in structural size and wing stripe of Lesser and Greater scaup

Abstract

Heads, wings, and feet of Lesser Scaup (Aythya affinis) and Greater Scaup (Aythya marila) were obtained from 365 birds killed by hunters to investigate differences in structural size and in the intensity and extent of the white wing stripe. Twelve morphological measurements were taken on each bird and wing stripes were quantitatively scored using soil colour charts. Principal component analysis of the structural data separated the birds into two nonoverlapping size groups. We considered the group of large birds and the group of small birds to be Greater and Lesser scaup, respectively. Variation in the wing stripe character was extensive; 9% of the birds in our sample could not be correctly classified as Lesser or Greater scaup on the basis of wing stripe alone. However, most of the variation was due to sexual differences, i.e., female Greater Scaup with unusually dark wings and male Lesser Scaup with unusually white wings.