Conservationists long have recognized the hemispheric significance of waterfowl and other migratory birds that move twice a year along North AmericaÃ¢â¬â¢s four great avian flyways. Ducks, geese, shorebirds, and warblers that may breed and raise young in the Arctic, along the Aleutian Islands, in CanadaÃ¢â¬â¢s vast prairie provinces, or even as far away as northern Japan and Siberia, may winter in the Caribbean, on MexicoÃ¢â¬â¢s Yucatan Peninsula, or along the southern tier of states that border the Rio Grande. By mid-century, U.S. Fish and Wildlife Service and Canadian Wildlife Service biologists were working cooperatively to monitor and manage duck and goose populations that breed in the far north. Where governmental agencies were limited in their ability to work and to invest funds in other countries, private conservation organizations like Ducks Unlimited stepped in and brought the greater flexibility of the private and non-profit sectors to wildlife management. Here, Ducks Unlimited project supervisor Fred Sharp operates an airboat of classic traditional design on Lake Newell near Tilley, Alberta, Canada, during duck banding operations in 1951. Airboats still are an important mode of transportation on waterlogged national wildlife refuges; the air thrust boat was invented by Fish and Wildlife Service employees G. H. Jensen and Cecil Williams in 1943 at Bear River National Wildlife Refuge in Utah.Hide.