Introduction

While much of the (avi)fauna of the southern hemisphere is unique, most of the water-, shore- and seabirds have close ties with the northern hemisphere. Some of the latter are closely related to species breeding further north, while others only visit the southern hemisphere as non-breeders. This is not surprising. Waterbirds are highly mobile and many species can disperse over very long distances. However, within the waterbirds, there is a puzzling bias in the taxonomic distribution of species that breed in the southern hemisphere versus those that only visit during the non-breeding season. The majority of waterbird groups have breeding representatives on both hemispheres. For example, we find breeding ducks, cranes, herons and gulls in both the southern and the northern hemisphere. Only a small number of high-latitude taxa, such as penguins and diving petrels in the Antarctic and divers and alcids in the Arctic are restricted to one hemisphere. The major exception to this pattern are waders. Many waders of the genera Calidris, Tringa, Pluvialis, Limosa and others visit the southern hemisphere each year in large numbers. None of these has established breeding populations in the south. The reason for their remarkable absence as breeders is the topic of this chapter.