The Pectoral Sandpiper breeds both in Siberia and Alaska as well as the Canadian Arctic. It is a long distance migrant, with the bulk wintering in South America’s Southern Cone. Some also winter in Australasia, likely some of the Siberian breeders? This larger Calidris sandpiper is identified by its dark breast streaking which stops at a bold clean break on the breast, or pectoral area, giving the bird its name. This is a shorebird that has a highly skewed breeding sex ratio, males are under very high pressure to compete and obtain a territory to which he attracts many mates. This highly competitive scenario for males has selected for very large size in that sex, and creates marked sexual size dimorphism. Males are clearly larger than males when seen side-by side. It is not known if males and females winter in the same areas, but probabilities are that the very different sizes also means that they may take different ecological niches and may even be wintering in different areas. More needs to be worked out on the wintering distribution and ecology of this species. In summer male Pectoral Sandpipers give an astounding display, flying low over the tundra with inflated air sacs in their neck while uttering a strange booming sound.