Maintenance of population structuring in sympatric-wintering populations of Greater White-fronted Geese Anser albifrons: behaviour, ecology and landscapes

Population structuring, although most common in sedentary organisms (Arguedas & Parker 2000), is well documented in migratory birds, including waterfowl (Zink 1996). In polytypic species it is generally presumed that phenotypic variation, and some level of population genetic structuring, is an outcome of natural selection, with different forms adapted to specific environments or habitats (niches). Identification and quantification of “ecotypes” is a priority among conservationists and resource managers, as maintenance of genetic diversity is a common goal in wildlife conservation (Avise & Hamrick 1996). Once distinctive forms are identified then it becomes imperative to discover the mechanisms sustaining population structure with the objective of enhancing long-term persistence. There is little empirical data on the behaviour and distribution of sympatric wintering subspecies or populations of waterfowl or documentation of potential isolating mechanisms. In North America, research on gene flow and population structuring among various forms of the Mallard Anas platyrynchos have focused on comparisons with the more geographically restricted, and habitatdependent Black Duck Anas rubripes; Merendino et al. Maintenance of population structuring in sympatric-wintering populations of Greater White-fronted Geese Anser albifrons: behaviour, ecology and landscapes