. Bulletin - United States National Museum. Science. MIGRATION AND ORIGINS 279. Figure 9.—Hypothetical life zones of the Wisconsin age: (A) arctic glaciation, (B) tundra, (C) Hudsonian, (D) Canadian, (E) Transitional, (F) Upper Austral, (G) Lower Austral. Heavy broken line marks the limit of 20-inch mean annual rainfall. (From L. S. Dillon, "Wisconsin Climate and Life Zones in North America," Science, vol. 123, fig. 11, 1956.) that some are of eastern and Asiatic species show that birds from all sources became differentiated by their relation to the Alaskan nesting grounds. , Some ha
. Bulletin - United States National Museum. Science. MIGRATION AND ORIGINS 279. Figure 9.—Hypothetical life zones of the Wisconsin age: (A) arctic glaciation, (B) tundra, (C) Hudsonian, (D) Canadian, (E) Transitional, (F) Upper Austral, (G) Lower Austral. Heavy broken line marks the limit of 20-inch mean annual rainfall. (From L. S. Dillon, "Wisconsin Climate and Life Zones in North America," Science, vol. 123, fig. 11, 1956.) that some are of eastern and Asiatic species show that birds from all sources became differentiated by their relation to the Alaskan nesting grounds. , Some hardy species of birds, like those which winter in the Arctic may have survived in ice-free lowlands of northern Alaska and Yukon, during maximum glaciation in the Mankato substage of Wisconsin time but land birds could not migrate over continental ice caps. The migratory populations now nesting in the northern part of America must, therefore, have become established within the last 10,000 years. During the earlier glacial maxima of Wisconsin time the existence 469496—60 19. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.
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