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Vol 3 No 2
Dec 95
Bird
Migration and the role of Sungei Buloh
Our Baby
Tailorbird
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 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
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For
those who have thought about the problems involved, navigation is the most
mysterious aspect of migration. The vast distances involved and the
tremendous feats of endurance performed by the birds only serve to
underline this most wonderful part of the whole phenomenon—the fact that
the birds are able to find their way on long-range flights often to return,
year after year, to exactly the same breeding site.
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The word "migration" is derived
from the Latin "migrare" meaning to
move from one place to another. Migration is the regular and usually annual
movement of a population from a breeding area to a non-breeding area, and
the return of most of these individuals to the breeding area.
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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.
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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.
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The East Asian Flyway
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 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.
Sungei
Buloh Nature Park
The Sungei Buloh Nature
Park is situated along a major migratory route, the East Asian Flyway. During
the migratory season from September to March each year, migrants stop over at
the Park before moving on with their journey. Waders like the Redshanks, Whimbrels and Plovers can be seen in hundreds, sometimes
thousands, on the mudflats. Other birds like the reed-warblers, kingfishers
and bee-eaters are also common migrants, among the trees and shrubs
surrounding the ponds. Our unique mangroves, mudflats and freshwater habitats
provide suitable conditions for both waders,
passerines and other birds to feed and roost, and rare opportunities for
visitors to enjoy the flight antics and sights of these feathered visitors
from afar.
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