Since 1948, this concept served as the basis for administrative action by the Fish and Wildlife Service in setting annual migratory waterfowl hunting regulations.
The concept of bird populations being confined to four fairly definite and distinct migration "flyways" is probably most applicable to those birds that migrate in family groups, namely geese, swans, and cranes, but does not appear to be very helpful in understanding the movements of the more widely dispersing ducks. The "pioneering spirit" in Canada geese, for example, is limited by their social structure the young travel to and from specific breeding and wintering areas with their parents. These young later in life usually breed in the same areas as did their parents. If a goose population is decimated in one flyway, either by hunting or natural calamities, other goose populations in other flyways are not seriously endangered, but also these populations are very slow to repopulate an area where the previous goose population had been decimated. This is not the case with ducks because these birds are not always bound by their intrinsic behavior to return to specific breeding areas. Consequently, vacant breeding areas are more rapidly repopulated by ducks than by geese.
Although Lincoln's analysis was confined to ducks and geese, some thought that it applied to other groups of birds as well. Everyone now realizes that the concept of four flyways, designated as the Atlantic, Mississippi, Central, and Pacific Flyways, was an oversimplification of an extremely complex situation involving crisscrossing of migration routes, varying from species to species. It can be considered meaningful only in a very general way, even for waterfowl, and not applicable generally to other groups of birds. Nevertheless the four "Flyway" areas have been useful in regionalizing the harvest of waterfowl for areas of different vulnerability of hunting pressure.
Bellrose (1968) identified corridors of southward migrating waterfowl east of the Rocky Mountains and determined, through statistical analyses, the relative abundance of birds in each. He showed major corridors of dabbling duck movements down the Great Plains and Missouri-Mississippi river valleys with minor off shoots at various points from these corridors eastward to the Atlantic coast where they joined equally minor eastern movements from the North (Fig. 13). Bellrose's map of migration corridors for the diving ducks showed heavy traffic similar to that of dabbling species down the Great Plains and relatively heavily used corridors from these central arteries eastward across the Great Lakes area to the Atlantic coast, terminating particularly in the vicinity of Chesapeake Bay. A fairly well-used corridor extends along the Atlantic coast.