Migration

Migratory Birds
Birds and other animals migrate because of changes in weather. Before the onset of winter, they move to where it is warmer and where there is food supply. Among all animals, birds have the longest migratory range. Migratory birds may fly thousands of kilometres to spend the winter in the south where it is warmer. Waders migrate from their breeding grounds in Siberia and northern Asian countries to warmer regions in Southeast Asia and the Southern Hemisphere. Waders are not the only birds that migrate. Other migratory birds include warblers, swifts, swallows and kites.

Finding the way

There are many theories on how birds navigate. The Circadian Rhythms and the Celestial Navigation theory proposes an internal clock in a bird for full celestial navigation. Important navigational tools would include visual markers like landmarks or clues from taste, smell, light, dye or anything familiar emanating from a particular direction. Birds could also orientate with a fair degree of accuracy with reference to the direction of the sun, the stars and cues from the earth's magnetic field.

There are many paths, or flyways, taken by the majority of the migratory species. The route of migrating birds will often take them over areas totally inhospitable to the species. Land birds make long ocean crossings, water birds traverse the deserts and open country species fly over forests. In all cases the migrants are only likely to come to ground where they find a suitable habitat. This poses a problem for species which are site specific. These sites take on a very special significance and might, with some species, be so important that their loss could cause extinction of the species.

The East Asian Flyway

Waders
Waders are some of the longest distance migrants. Many species of waders previously considered to be exclusive birds of the coastal and estuarine mudflats achney rnigrate overland. It has since been realized that vast distances are covered overland and across open seas on each migration by many species of waders. Waders are so called because they frequent coastal mudflats, wading about in the nutrient-rich mudflats to feed during low tide.

Stopover-sites
For most long-distance migrants, the amount of reserves stored before migration is insufficient to allow them to make the entire flight without rebuilding reserves. Thus, migration must involve a wavelike alteration of migrating and feeding activity. Migrants make use of stopover sites like the ones found in the Park for refuelling before moving on again. Birds have evolved food gathering adaptations that enable them to feed on different types of organisms instead of depending on a particular species of organisms. Thus the Arctic wader that feeds on small worms in a sandy substrate is equally well equipped to feed in a muddy mangrove mudflat, like those found in the Park.

Survival Strategies
The storage of fat reserves under the skin is an important adaptation of the migrant. The capability of forming such reserves is critical to survival in a competitive environment.

Territorial behaviour is another way in which the birds increase their chances of survival at stopover sites. Birds defend their territory against other birds of the same species to minimise competition for the limited food supply available.

Individuals of most species of transients migrate at night to avoid air turbulence caused as the sun heats the earth's atmosphere, and perhaps to minimise threat of predation. Transients are birds that stop over at a location before moving on again.

Migratory birds also fly in certain formations. One of them is the well known "V" formation. The aerodynamics of flying in this formation results in less energy spent during flight.