Monday, Jul. 19, 1948
Fossil Flight Plan
Migrating birds are excellent navigators, hitting small oceanic islands like radio-guided airplanes. But some of them seem to cross unnecessary oceans. The Arctic tern, for instance, nests in summer in North America; when winter approaches, it heads for Antarctic regions near South America. But instead of flying south, the most direct route, it heads eastward across the North Atlantic to Europe, then down the African coast and across the South Atlantic. Other birds that migrate long distances take similar detours. All this tends to vex and confuse the ornithologists, who want to know why birds behave that way.
In !ast week's Science magazine, Dr. Alber Wolfson of Northwestern University advances his explanation: that they are led astray by the earth's fickle geology. According to a fairly well established theory, says Dr. Wolfson, the continents were once bunched together in two main masses: "Laurasia" (North America and Eurasia) and "Gondwana" (South America, Africa, Antarctica, Australia), which were separated only by shallow seas (see map). During the Cretaceous period, 60 million years ago, both masses broke up and drifted slowly apart, their light granitic rocks floating on the heavy, plastic basalt that underlies both the oceans and the land.
By the time this movement got under way, birds had already evolved into modern types. Dr. Wolfson thinks that some of them had learned to make comparatively short seasonal migrations between feeding and nesting places, that generation after generation, for millions of years, they stuck to the same routes. New oceans appeared and widened under their beating wings. New mountains reared up. The climate changed as glaciers crept forward, then melted. The birds, more steadfast than the earth, kept to their ancient flight plan, though their journeys became much longer than at first and twice as long as need be.
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