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 THE. C9ITB .R Volume XVII November-December, 191. Number  THE YELLOW-BILLED LOON: A PROBLEM IN MIGRATION By WELLS W. COOKE HE MIGRATION route of the Yellow-billed Loon (Gavia adamsi) is prob- ably the most incomprehensible problem of migration on the North Amer- ican continent. The species breeds on the Arctic coast from Franklin Bay, just east of the mouth of the Mackenzie River, along the whole of the 'Arctic coast of Alaska, and on the Siberian side west certainly to the Chukchi Penin- sula and probably to the mouth of the Kolyma River. The only place where the species has been found in numbers during the winter season is on the coast of Norway. Here, on the northwest coast in the neighborhood of Tromso, it was common the winters of 1892-3 and 1893-4, and many specimens were taken from September to January. It also ranged along the whole west coast even to the southern end. In addition it is known in winter in Japan and China and as a rare spring and fall migrant around the Sea of Okhotsk. It is unknown in winter anywhere in the Western Hemisphere and there are no records of its occurrence in this half of the world between November and May. It is known to breed in the Mackenzie Valley along the seacoast, and during the summer visits Great Slave Lake, arriving at the western end in May and being present at the eastern end until late October. It is common here in August and early September, and is still more common on Clinton-Colden and Aylmer lakes. The problem is as to whence come the early May birds and whither go the late fall birds. Since the species is unknown anywhere in the Western Hemisphere in winter, it follows that the breeding birds of the Mackenzie coast winter some- where in the Eastern Hemisphere, presumably in Japan and China, though the numbers reported from anywhere in eastern Asia in the winter are very small compared with the multitudes recorded throughout the great extent of the summer home. Apparently the real winter home of the great bulk of the species has not yet been discovered. But assuming that the winter home is somewhere in eastern Asia, then the birds in spring must go on the Asiatic side to the Arctic Ocean and then eastward