Tai O Biodiversity
by Thomas Gomersall
Many people come to the coastal Lantau village of Tai O for its traditional stilt houses (some of the last in Hong Kong), dried-shrimp paste, or Chinese white dolphin watching tours.
But many walk past its local mangrove swamp without a second glance.
This is understandable as Tai O does not have the abundance of birdlife at Mai Po Nature Reserve, and what species that do live here are mostly secretive. The most obvious section of mangrove swamp is boxed in on nearly all sides by the nearby road, pier and sea wall all lined with pink fencing that somewhat resembles a giant museum exhibit. And sadly, like all too many coastal areas, plastic clings to the tideline like barnacles to a rock.
Still, a surprisingly rich mangrove community exists here. Fish dart around the rocks near the sea wall while fiddler crabs creep about on the mudflats. Meanwhile, herons wade out into the shallows to catch small sea creatures, joined sometimes by local fishermen trying to do the same. Like much of Hong Kong’s wildlife, the animals and plants here are resilient, clinging to survival on the edge of the human world that continues — in one way or another — to encroach on theirs.
Mangrove Water Snake (Enhydris bennetti): With its extensive intertidal mudflats, Tai O is one of only two places in Hong Kong (the other being Deep Bay) where you can find the mangrove water snake. A specialist of muddy coastal habitats, it is active both day and night and feeds on small fish. It has large, open nostrils on the top of its snout for breathing when swimming beneath the water surface. While not an aggressive snake, it is mildly venomous and will bite if disturbed (Chan et al, 2006, p. 77).
Fiddler Crab (Uca): There are six fiddler crab species in Hong Kong (five of which can be found in Tai O) and they all have one unique feature in common: a spectacularly oversized claw in the male. This claw, which can be up to three times the length of the crab’s body, is used by the males to compete with each other, usually through display but in some species, the claw is used to make noise too. Amazingly, if a male’s big claw breaks off, his small claw will grow into a new big claw while a new small claw will grow in the place of the old big one. Specialists of intertidal estuarine habitats, crowds of fiddler crabs can be seen crawling around on the mud at low tide, picking through the sediment for food. The soft substrate is also good for digging in burrows, which provide the crabs with shelter and help to oxidate the otherwise oxygen-poor mud, increasing decomposition rates and microorganism growth that in turn provide more food for the crabs (Kwok & Tsang, 2006).
Red-billed Starling (Spodiopsar sericeus): Starlings as a group are very sociable, very noisy birds. And in Hong Kong, there is perhaps no better example of that than the red-billed starling. This winter visitor to open lowland areas forms enormous, highly vocal flocks, sometimes in excess of 3,000 birds (Viney et al, 2005, p. 220). Smaller groups do sometimes remain in Hong Kong to breed over the summer (Tipper, 2016, p. 128). Adult males have creamy-white heads while females have darker ones.
Little Egret (Egretta garzetta): Along with its larger cousin, the great egret (from which it is distinguishable by its smaller size, black beak and bright yellow feet), the little egret is one of Hong Kong’s most adaptable birds, found anywhere where there is water and small aquatic animals to eat. While its commonness may cause people to overlook the bird, the little egret does have a few neat hunting tricks up its sleeve. The most dramatic of these is called ‘foot stirring’, in which the bird will erratically run around in the shallows with its wings raised (Tipper, 2016, p. 29). Despite being a common bird, its long-term survival may be threatened by water pollution, particularly by pesticides like DDT, which has been found in high concentrations in the eggs of little egrets in Hong Kong (Connell et al, 2003). DDT thins the shells of bird eggs, causing them to break when the parents sit on them.
Four-spot Midget (Mortonagrion hirosei): A globally threatened damselfly, the four-spot midget is confined to coastal areas of Hong Kong, Guangdong, Taiwan and the east coast of Honshu in Japan. Unusually for a damselfly, most species of which live exclusively in freshwater habitats, the four-spot midget is a halophile (salt lover), whose nymphs can survive in brackish water (IUCN Red List, 2011). Meanwhile, adults can be found in mangroves, reed beds and coastal marshes with short, dense grass (Tam et al, 2011, p. 118). This uniqueness in habitat preference makes it very vulnerable to coastal development, which is the main reason for the four-spot midget’s rarity (IUCN Red List, 2011). As its name suggests, it can be identified by the four green spots on its thorax.
· Chan, S., Cheung, K.S., Ho, C.Y., Lam, F.N., Tang, W.S. and J.M.L. Tse. 2006. A Field Guide to the Venomous Land Snakes of Hong Kong. Agriculture, Fisheries and Conservation Department. Hong Kong SAR Government. 77pp.
· Connell, D.W., Fung, C.N., Minh, T.B., Tanabe, S., Lam, P.K.S., Wong, B.S.F., Lam, M.H.W., Wong, L.C., Wu, R.S.S. and B.J. Richardson. 2003. Risk to breeding success of fish-eating Ardeids due to persistent organic contaminants in Hong Kong: evidence from organochlorine compounds in eggs. Water Research, vol. 37: 459pp.–467pp.
· IUCN Red List, Four-spot Midget, [website], 2011, https://www.iucnredlist.org/species/13891/4362234 (Accessed: 16th April 2019).
· Kwok, W.P.W and Tang, W.S. 2006. Fiddler Crabs in Hong Kong- An Overview. Hong Kong Biodiversity, Agriculture, Fisheries and Conservation Department Newsletter, 12: 1pp.-7pp. https://www.afcd.gov.hk/english/publications/publications_con/files/hkbonewsletter12.pdf (Accessed: 16th April 2019)
· Tam, T.W., Leung, K.K., Kwan, B.S.P., Wu, K.K.Y, Tang, S.S.H, So, I.W.Y., Cheng, J.C.Y., Yuen, E.F.M, Tsang, Y.M. and W.L. Hui. 2011. The Dragonflies of Hong Kong, first edition., Friends of the Country Parks, Hong Kong. 118pp.
· Tipper, R. 2016. A Naturalist’s Guide to the Birds of Hong Kong, John Beaufoy Publishing, United Kingdom. 29pp., 128pp.
· Viney, C., Phillipps, K. and C.Y. Lam. 2005. The Birds of Hong Kong and South China. Information Services Department, Hong Kong SAR Government, Hong Kong. 220pp.