Creatures as diverse as Monarch butterflies, Green sea turtles, Arctic terns, Ruby-Throated Hummingbirds, and salmon all must coordinate a complex series of factors - body mass, time of migration, food availability, weather, global position (without benefit of landmarks for pelagic migrants) - all, in the case of young of the year, without ever having done it before. How did such astonishing abilities evolve when the costs and risks to the organism are so high and the benefits so seemingly minor? Here's Deyes:
Those in favor of evolution's ways openly struggle to understand the selective advantage afforded by the migratory birds' seemingly deliberate draining of precious resources. By their own admission "Migration exacts a high toll [as] grizzlies wait in streams and gorge on exhausted salmon migrating home from the sea, and falcons feast on fatigued songbirds arriving at their winter home in Africa. Fuel used by muscles to propel wings, fins, and legs is unavailable for reproductive activities, and time spent on the move is time not spent gathering food." They counter their self-imposed quandary by assuming a priori that selection 'favors the brave' and that over time survival benefits must have outweighed such costs. Evolution is after all a 'fact' and so what must have happened must have happened. Such circular reasoning of course gets us nowhere and leaves the above functional challenges unanswered.
Migration is indeed a mystery - a mystery in terms of how it's accomplished and a mystery in terms of why and how it ever evolved. Of course, if the evolution of this amazing behavior were directed by an intelligent agent a big part of the mystery, though certainly not all of it (the question of how the agent did it, for example, would still remain), would be cleared up.RLC