TNAG-0532-FCO40-627-Conservation-of-wildlife-in-Hong-Kong-1976 — Page 57

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6.3

6.2.6 Appendix 3 gives a selective list of the birds recorded from the Deep Bay/Mai Po Area. This is not intended as a comprehensive check-list, but as a list of the more restricted species for which the Marshes often represent the only extensive area of suitable habitat in Hong Kong.

6.2.7

The numerical status of the species listed should be regarded as tentative (probably underestimates). Host observations have been limited to weekends and

the unpredicatable tides and the way in which the kei wais are operated have resulted in little consistency between observations.

6.2.8

It is known from radar observations that large numbers of birds pass over Hong Kong during periods of migration and the character and behaviour of many of the echoes suggest flocks of wading birds (Myres and Apps. 1973, Melville unpublished observa- tions). On the Marshes, disturbance by illegal notting and shooting and other human activities almost certainly keeps the bird population at a lower level than the actual holding capacity of the site. Since no ringing studies have been made of waders it is not possible to consider the throughflow of migratory birds.

Other fauna

6.3.1 Besides birds, the Marshes contain a rich concentration of other fauna. Many of these animals are intimately related to the mangrove community and the environmental conditions which it creates.

6.3.2 Living on the leaves of the plants is the littorine mollusc Littorina melanostoma and a whole range of insects, particularly those which use the leaves as places to lay their eggs, and leaf miners and borers. The water snake Enhydris bennetti, which may be restricted to south-east China, lives among the branches. The stems of the mangroves are colonised by barnacles (Chthalmus, Balanus) and oysters (Saccostrea), which are typically genera found on rocky shores. A number of other gastropods and bivalves, the polymorphic snail Clithon oualaniensis, the mangrove shrimp Laeomedia astacina, and some molluscs of primarily terrestrial origin live in or on the mud between the mangrove roots. Crabs of the mangrove region include Sesarma sinensis, the fiddler crab Uca dussumieri and the predacious swimming crab Scylla serrata. The Uca and Scylla crabs are adapted for a partially terrestrial existence since the walls of the branchial chambers arc vascularised to supplement their gills.