Morphological Differences in Pacific Coast Populations of Greater White-Fronted Geese

Abstract

We examined morphological relationships of three Pacific coast populations of Greater White-fronted Geese (Anser albifrons). Adult geese were captured and measured at three breeding areas in Alaska and two wintering areas in California, 1980-1991. A two-step discriminant function analysis examined morphological differences among the three populations. Stepwise discriminant function procedures created the simplest measurement models. Each sex was analyzed separately since multivariate analysis of variance indicated that males were significantly larger than females for all three populations. Tule Greater White-fronted Geese (A. a. gambelli) were significantly larger than Pacific Greater White-fronted Geese (A. a. frontalis), hereafter Pacific Geese. The first step of discriminant function analysis created models to differentiate Tule Geese from the Pacific Geese. Bivariate stepwise discriminant function models consisting of only two measurements correctly classified 92% of males (bill height, bill width) and 96% of females (bill height, culmen) of these subspecies. The second step of discriminant function analysis compared a small population of Pacific Geese from the Bristol Bay Lowlands (BBL) of southwestern Alaska with the large population of Pacific Geese that breed on the Yukon-Kuskokwim River Delta (YKD) of westcentral Alaska. We developed models with three (culmen, diagonal tarsus, midtoe) and five (culmen, diagonal tarsus, midtoe, total tarsus, bill height) measurements from stepwise discriminant function analyses to correctly classify 72% of males and 74% of females of these populations. Thus, morphology of Tule Geese differed highly significantly from Pacific Geese, as expected, but differences between populations from the BBL and YKD areas were also significant. Morphometric analyses as these provided supporting evidence for clinal variation in populations of Greater White-fronted Geese. They also underscore a need for further studies of differences among North American populations of Greater White-fronted Geese to resolve classification and to allow formulation of subpopulation/subspecies management strategies.