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 sprinkled liberally 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. Granted, not all of North America’s migrating birds can winter in the same spot, but why do some migrators stop when they reach the Gulf Coast states (the house wren, for example) while others (such as the dickcissel) aren’t happy until they hit Venezuela?

Moving from one not-totally-explained fact to another brings us to what triggers migration. It’s often heard weather is a factor, which certainly explains why severe cold fronts up north will always spur large flights of snow geese, ducks, bald eagles and other birds to fly south. However, it doesn’t explain why these same species (albeit often in lesser numbers) still migrate south in mild winters.

Shortening periods of daylight (photo period) is another instinctual key that is theorized to triggers the migratory travels in many species. However, even with this there’s variance as evidenced by the fact that some species begin migrations in late August while others start later in the fall.

Probably, the best way to explain bird migration is that it very likely involves several of these factors and a few others, too. Shortening days, combined with changing temperatures, food availability and, perhaps for some species, an instinctual knowledge of an ancestral home range that existed when glaciers altered habitats over much of North America are all likely factors that drive birds south in the fall. These are among the reasons that drive tiny hummingbirds to make continuous flights of more than 20 hours from the southern coast of the U.S. across the Caribbean Sea to winter homes in Central America. They’re part of the reason Arctic terns make an 11,000-mile trip each autumn from its summer breeding ground above the Arctic Circle to a winter home in Antarctica – and then make the return trip north in the spring. They’re part of the reason some waterfowl can cover more than 400 miles in a single 10-hour flight.

Most importantly for us humans, these are reasons why migration time is the time to get a bird book, grab some binoculars and head outdoors. Bring a journal to record the bird species you see. This isn’t a necessity for finding birds, but it makes your trips more interesting when, over a period of time, you start to discover the diversity of birds that migrate through this area.

Your nearest Missouri Department of Conservation office has literature about birds and information about nearby areas that have fall birding potential. Bird information can also be found at www.missouriconservation.org. In Springfield, one place to look for migrating birds in the fall is the Springfield Conservation Nature Center.

In addition to visiting the Springfield Nature Center for traveling birds, be sure to attend the Nature Center’s Oct. 10 program “Missouri’s Black Bears.” The program begins at 5 p.m. and attendees are invited to stay for MDC’s 80th Anniversary Open House event which will be 6-8 p.m. at the Nature Center. At this event, people are invited to join Missouri Department of Conservation Director Sara Parker Pauley, the Conservation Commissioners and local leaders to celebrate the Department’s history and share ideas about the state’s conservation future. No registration is required for the bear program or the open house event.