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... To complete its annual return journey between northerly breeding latitudes and tropical winter regions, a tiny songbird must keep to seasonal and daily timetables, change its physiological machinery between phases of fuel consumption and fuel deposition, vary flight steps and fuel loads in relation to the crossing of benign or hostile regions, find its way by compass and navigation systems, negotiate weather and winds, and correctly adjust flight speed and altitude. The bird's endowment with all necessary instructions represents a striking manifestation of the accomplishments achieved by biological evolution.
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