5. Flyway

Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements occur as a response to changes in food availability, habitat, or weather. Approximately 1800 of the world's 10,000 bird species are long-distance migrants [35]. The bar-tailed godwit, Limosa lapponica, undertakes one of the avian world's most extraordinary migratory journeys. Recent research revealed that some individuals had made nonstop flights over 11,000 km, the longest continuous journey that has ever been recorded for a bird [36].

Many species migrate along broadly similar, well-established routes, known as flyways. Recent research has identified nine such pathways: the East Atlantic, the Mediterranean/Black Sea, the West Asia/East Africa, the Central Asia, the East Asia/Australasia, and four flyways in the Americas [37]. The most common pattern involves flying north in the spring to breed in the temperate or Arctic summer and then returning south in the fall to warmer wintering grounds. Migration is often annual and is linked closely with the cyclic pattern of the seasons. Migration is most evident among birds, which have a highly efficient means for traveling swiftly over long distances.

The East Asia/Australasia flyway extends from Siberia and North America to the southern limits of Australia and New Zealand. It encompasses large parts of East Asia, all of Southeast Asia, and includes eastern India and the Andaman and Nicobar Islands. The scale of avian movements along the flyway is awesome, with over 50 million migratory birds using the route annually [38]. Bacterial community compositions in migratory birds from the East Asia/Australasia flyway are described in the section below.
