1 Foraging: An Overview Hudson Bay in winter is frozen and forbidding. But, at a few special places where strong tidal currents are deflected to the surface by ridges on the seafloor, there are permanent openings in the ice, called polynyas, that serve as the Arctic equivalent of desert oases. | Illllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll 1 Foraging An Overview Ronald C. Ydenberg Joel S. Brown and David W. Stephens Prologue Hudson Bay in winter is frozen and forbidding. But at a few special places where strong tidal currents are deflected to the surface by ridges on the seafloor there are permanent openings in the ice called polyn-yas that serve as the Arctic equivalent of desert oases. Many polynyas are occupied by groups of common eiders. When the current in the po-lynya slackens between tide changes these sea ducks can forage and they take advantage of the opportunity by diving many times. With vigorous wing strokes they descend to the bottom where they search though the jumbled debris finding and swallowing small items and occasionally bringing a large item such as an urchin or a mussel clump to the surface where they handle it extensively before eating or discarding it. Readers can take an underwater look at a common eider diving in a polynya at eidervideo . These videos were made by Joel Heath and Grant Gilchrist at the Belcher Islands in Hudson Bay. This foraging situation presents many challenges. Eiders must consume a lot of prey during a short period to meet the high energy demand of a very cold climate. Most available prey are bulky and of low quality and the ducks must process a tremendous volume of material to extract the energy and nutrients they need. They must also keep an eye on the clock for the strong currents limit the available foraging time. lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll 2 Ronald C. Ydenberg Joel S. Brown and David W. Stephens Throughout the winter individual ducks may move among several widely separated polynyas or visit leads in the pack ice when the wind creates openings. Foxes haunting the rim of the polynyas and seals in the water below create dangers that require
