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Importance of Kranji Marshland for Nature
Apart from the birdlife, it must be said that very little is known of the biodiversity of the Kranji Reservoir environs. The Kranji Reservoir environs, with its variety of land cover and habitats, harbour an abundant birdlife that is rich in species.
The Reservoir marshes are the stronghold of the Grey Heron (Ardea cinerea) and Purple Heron (Ardea purpurea). The Grey Heron is a Nationally Threatened Species, while the Purple Heron is a Nationally Near-threatened Species (Lim, 1999). The Grey Heron is omnivorous and tends to be gregarious. They are concentrated in large numbers at the lower part of the Kranji Reservoir - especially at the mudflat to the east of the Kranji Bund and the bay at the edge of the Kranji Radio Transmitting Station. A survey in 2000 revealed that out of 66 Greys recorded, 56 (85 per cent) are found in the Lower Kranji Reservoir area (Ho, 2000). Observations have shown that the nesting Greys at the Sungei Buloh Nature Reserve, about 2 km away to the north, resort to the reservoir for food to feed their nestlings. Currently, there is no known existing Grey heronry in the marshes. In the past, the largest known Grey heronry in Singapore with about 60 nests was located in a remnant mangrove patch in the South Kranji Bund Marsh (Wells, 1999). This patch, together with the heronry, has been overwhelmed by development.
The Purple Heron is just as conspicuous as the Grey but they do not usually congregate in groups when feeding. The species is also omnivorous, but fish predominates, accounting for more than 50 per cent of its diet (Hancock & Elliott, 1978). Unlike the Grey, they prefer feeding grounds that are grassier and less muddy. The Survey in 2000 shows that out of 49 Purple recorded, 33 (67 per cent) are found in the upper reservoir areas (Ho, 2000). Most of those in the Kranji Bund area are actually seen at the edge or within the marshes.
Also, unlike the Grey, the Purple has a preference for nesting in ground ferns or tall grasses (Hancock & Elliott, 1978), although trees are not excluded as in the mixed heronry with the Grey at Sungei Buloh. There is a record in 1983 of 20-30 pairs nesting in the Acrostichum ferns of the Reservoir marshes (Wells, 1999), but it is now uncertain whether nesting in the ferns or any other parts of the Reservoir still goes on. Like the Grey, observation has shown that the nesting parents as well as immatures from the Buloh heronry resort to the Reservoir marshes for food.
Rails are typical freshwater marshland birds. Eight species are found in the Reservoir marshes. The most conspicuous in terms of its size and colour is the Purple Swamphen (Porphyrio porphyrio). An uncommon resident species, the Swamphen is also a Nationally Near-threatened Species (Lim, 1999). It breeds only in two areas of Singapore - in the Kranji Reservoir and the Western Catchment (Lim, 1992). It is usually seen foraging for plant and other food by the edge of the Kranji Bund Marshes. The most commonly seen rail is the pretty White-breasted Waterhen (Amaurornis phoenicurus), thriving wherever there is a pond, river, stream or an old monsoon drain. Seven other species of rails are also found here, such as the Slaty-breasted Rail (Gallirallus striatus), White-browed Crake (Porzana cinerea) and Ruddy-breasted Crake (Porzana fusca).
Another group of birds that is also specially adapted to the marshland habitat is the reed-warblers. Four species, all winter visitor/passage migrant, are found in the Reservoir marshes. Nervous and shy birds, they are not easily seen by casual observers. The most common is the Oriental Reed-warbler (Acrocephalus orientalis), whose presence in the tall grasses is usually announced by its shrill, agitated cries.
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