reserves to prepare for the next migratory stage; the route used on the spring migration may be different from that used in the autumn and will depend on such factors as wind direction and the availability of food at staging points. Flyways may not be the shortest route available but may have curves or doglegs. Birds of different species may follow similar routes, and populations from one area may merge with other groups and diverge to reach different destinations. Flyways tend to avoid obstacles such as mountain ranges and oceans, running parallel to the barriers and following routes along the coast or along major river valleys. Passerines often fly on a broader front across the terrain, either flying over or circumventing obstacles on the route, according to their evolutionary adaptations. In selecting routes, birds may overcompensate for predicted winds. Terrestrial birds tend to travel over land, raptors need routes where thermals can give them the lift they require, sea birds prefer ocean routes and wetland birds need routes with suitable staging sites; deltas and coastal wetlands provide reliable food sources for this purpose whereas inland wetlands are less predictable. Flyways of the Americas The Atlantic Flyway starts in northern Canada and Greenland and follows the Atlantic coast of Canada and the United States to the Caribbean Sea, and on to tropical South America. The Mississippi Flyway starts from northeastern Canada and passes over the Great Lakes, following the lower Ohio River, the Missouri and the Mississippi to the Gulf of Mexico, and on to Central and South America. There are no mountain barriers on this route. The Central Flyway starts from central Canada and crosses the Great Plains before continuing southwards to the Gulf of Mexico, merging with the Mississippi Flyway. There are no mountain barriers on this route. The Pacific Flyway is a north–south flyway for birds migrating from breeding grounds in Alaska and Canada to their overwintering areas in South America, some species travelling as far south as Patagonia. The Allegheny Front flyway in the central Appalachian Mountains is an important flyway for migratory birds traveling from their northern breeding grounds to their southern wintering sites. Flyways of Eurasia, Africa, and Australasia The East Atlantic Flyway starts from northern North America, Greenland, Iceland, northern Europe and western Siberia and leads to wintering areas in western Europe and North Africa, with some birds continuing down the west coast of