Much is still being learned about bird migration, but one fact can be said with absolute certainty: Birds do not fly to the moon in winter.
Of all the thoughts that have been given about the seasonal travels of birds, this theory from 1703 is probably the most far-fetched — both in terms of feasibility and mileage. History failed to record this theory’s author, stating only that it was “a person of learning and piety.” His “probable solution” to the annual disappearance of a number of bird species in winter was that they flew to the moon and spent the winter there.
Although fall bird migration does not involve lunar travel, there are many fascinating theories — and equally fascinating questions — about this seasonal occurrence. Much of what is known about fall bird migrations does not fall into the category of clear-cut, definitive facts. Instead, biologists’ knowledge about migration trend more towards general tendencies that are liberally sprinkled with variations.
For instance, generally speaking, one theory why birds migrate in fall is so they can stay in climates where food sources are readily available. An example of this is the number of insect-eating species that travel south to warmer regions where insects remain active. However, if you want a bird that doesn’t follow this theory, look no farther than the bluebird. Missouri’s state bird eats insects throughout spring and summer but doesn’t migrate. (Its diet switches to vegetative matter in winter.)
Food availability also doesn’t entirely explain why some birds fly a few states south while others travel far into the southern hemisphere.