THE ENVIRONMENT
10-15 metres, with a generally flat and featureless muddy seabed that slopes gently southwards. Several deeper channels occur in constricted tidal pathways, as for example in Urmston Road, the East Lamma Channel, Lei Yue Mun, Sheung Sz Mun and Lo Chau Mun.
During the Pleistocene geological period, the last two million years, world sea-level fell and rose at least once during each of the four major glaciations when water was taken up to form great ice sheets. In south-east Asia, the sea-level fell to between 120-150 metres below its present level, which would have exposed an area of continental shelf about 130 kilometres wide to the south of Hong Kong. During this low sea-level period the Pearl River deposited alluvial sand and silt as channels over this wide plain.
As the ice began to melt about 10 000 years ago sea-levels rose reaching their present level about 6000 years ago. The returning sea deposited fine clays and silts (marine mud) over the earlier alluvial deposits. Recent boreholes drilled offshore have revealed a sequence of up to 20 metres of marine mud overlying up to 60 metres of predominantly alluvial deposits which in turn overlie bedrock.
Terrestrial Fauna
The physical and climatic environment of Hong Kong provides woody and grassy habitats for a wide variety of native animal and plant life. Under the pressure of urbanisation, larger animal species are rarely seen, but reptiles and amphibians, birds and many kinds of insects are common.
Most of Hong Kong's countryside is protected by the Forests and Countryside Ordi- nance, the Wild Animals Protection Ordinance, the Country Parks Ordinance, and the Animals and Plants (Protection of Endangered Species) Ordinance.
One of the most important sites in Hong Kong for wildlife is the Mai Po Marshes. A restricted area under the Wild Animals Protection Ordinance and managed jointly by the Agriculture and Fisheries Department and the World Wide Fund for Nature (Hong Kong), it is an internationally significant site for migratory and resident birdlife. Its 380 hectares of mudflats, shrimp ponds and dwarf mangroves provide a rich habitat, particularly for ducks and waders. More than 250 species of birds have been observed in this area, and at least 110 of them are rarely seen elsewhere in the territory. Yim Tso Ha, also a restricted area, is the largest egretry in Hong Kong. Five species, the Chinese Pond Heron, Night Heron, Cattle Egret, Little Egret, Great Egret and occasionally the rare Swinhoe's Egret as well, nest there regularly. More than 1 000 egrets can be found there between April and September, the nesting season. Egretries are also found at Mai Po Village, A Chau, Jim Uk, Tsim Bei Tsui, Wu Shek Kok and Ma Tso Lung.
Although traditional fung shui woods near the old villages and temples are increasingly affected by development, they continue to provide a very important habitat for many birds. Reported sightings in wooded areas include an assortment of warblers, flycatchers and robins.
Areas around the Kowloon reservoirs are inhabited by monkeys that originated from those that either were released or had escaped from captivity. There are breeding groups of both Long-tailed Macaques and Rhesus monkeys. Smaller mammals are common, with the Woodland Shrew, House Shrew and bats being numerous in some rural areas. The Chinese Porcupine, with its strikingly-coloured black and white quills, is still present in parts of the New Territories and Hong Kong Island.
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