One of the most spectacular wildlife displays in the Taiga Shield is the explosive return of ducks, loons, geese, and swans during the spring migration. The area's abundant water attracts hundreds of thousands of birds, which come to nest or simply feed and rest before journeying farther north to arctic breeding grounds. As an ecological crossroads between two very different ecosystems -- the boreal and the arctic -- the ecozone offers a relatively wide variety of habitats for birds. Lakes, wetlands, and forests are interwoven with open shrublands and sedge meadows more typical of the tundra. The consequent overlap of arctic and boreal bird species gives this area a special richness. At the southern limit of their summer range are such species as the Arctic Tern, while a host of other water birds, including the Common Tern and White-throated Sparrow, reach their northern limit on the Taiga Shield. Among the mammals of the ecozone are Barren-ground Caribou, which migrate south from the tundra to their winter range in the taiga forest. Close to a million Caribou from the Bathurst, Beverly, and Qaminirjuaq herds in the Northwest Territories, and the Leaf River and George River herds of northern Quebec and Labrador, make this journey each fall and return to calve on the tundra each spring. Mice, Voles, Shrews, Weasels, Canids, and other carnivores, plus all the tundra dwellers such as the Grizzly Bear and Arctic Fox, make regular visits to the trees of the Taiga Shield. In all, there are about 50 species of mammals inhabiting the ecozone. The ecozone's waters, meanwhile, are home to Lake Trout, Lake Whitefish, Arctic Grayling, Burbot, and Northern Pike.