A flyway is a flight path used by large numbers of birds while migrating between their breeding grounds and their overwintering quarters. Flyways generally span continents and often pass over oceans. Although applying to any species of migrating bird, the concept was first conceived and applied to waterfowl and shore birds. The flyways can be thought of as wide arterial highways to which the migratory routes of different species are tributaries. An alternative definition is that a flyway is the entire range of a migratory bird, encompassing both its breeding and non-breeding grounds, and the resting and feeding locations it uses while migrating. There are four major north–south flyways in North America and six covering Eurasia, Africa, and Australasia. History The passing of the Migratory Bird Treaty Act of 1918 in the United States resulted in a need for more information on bird migration. Frederick Charles Lincoln was put in charge and improved methods for trapping and banding, developed record-keeping procedures, recruited banders, fostered international cooperation, and promoted banding as a tool for research and wildlife management. He found it was possible to establish the routes used by waterfowl during their annual migrations and he developed the flyway concept, a key idea in the management and regulation of hunting of migratory birds; by establishing the routes used, estimates of population sizes could be made and suitable protection could be put in place. The special vulnerability of waterfowl and shorebirds on their international migrations, with their specific needs for suitable wetland stopovers, resulted in the signing of the Ramsar Convention in 1971. As a result, over 2300 Ramsar sites have been established around the world, many being situated on flyways where they provide the vital habitat needed by the birds on their journeys. Flyways Many bird populations migrate long distances twice a year. The most common pattern involves flying north in the spring to breed in the temperate parts of the northern hemisphere or the Arctic during summer and returning southward in the autumn to wintering grounds in warmer regions, often on the other side of the equator. A similar pattern occurs in the southern hemisphere with birds flying south to breed and north to overwinter, but on a much smaller scale. The flyway, or route, taken by different bird species varies, but each population has its traditional staging points along the route where birds feed to build up their energy