Mai Po Biodiversity: Gei Wai
by Thomas Gomersall
Established after World War II by Chinese immigrants who settled in Deep Bay, gei wai are traditional brackish-water shrimp and fish farms that use more environmentally friendly methods compared to many modern farms. Instead of importing shrimp and fish fry, the farmers rely on tidal activity from the adjacent mangroves to flush them into the gei wai. Instead of sourcing feed from wild fish populations, they rely on the natural nutrients flushed in with the tide. And when the gei wai are drained for harvest, the farmers leave the smaller shrimp and fish behind to become food for the newly arriving migratory waterbirds.
This ecologically sound, low-impact approach has helped to sustain the lives of both farmers and the countless species of fish-eating animals of Mai Po, many of whom survive here in large part because they are allowed to eat the unwanted fish and shrimp after the gei wai are drained. The nutrients flushed into the gei wai also support smaller invertebrates and algae that attract other, non-fish eating animals. All of which makes the 16 gei wai of Mai Po an unmissable part of any birdwatcher’s trip to the reserve.
Northern Shoveler (Anas clypeata): Ducks are perhaps the most common group of birds to be found in the gei wai, and one of the most common of this group at Mai Po has to be the northern shoveler. It is also one of the most unique looking, thanks to its huge, shovel-like bill, which is even longer than its head (Viney et al, 2005, p. 48). It uses this bill to forage for small aquatic invertebrates and plant matter, sweeping it back and forth and using small serrations on the side to filter its food from the water (Hong Kong Wetland Park, 2019).
Common Moorhen (Gallinula chloropus): Unlike ducks, this shy member of the rail family is rarely seen on the open waters of the gei wai, preferring instead to stick to the well-vegetated fringes where cover is abundant (Tipper, 2016, p. 41). It is a resident species in Hong Kong and breeds here from April to September, during which time it will build a nest of sticks and reeds near the water’s edge (Viney et al, 2005, p. 82; Tipper et al, 2016, p .41). Despite the limited webbing between its toes, it is a good swimmer.
Eurasian Spoonbill (Platalea leucorodia): While watching the flocks of black-faced spoonbills that frequent the drained gei wai, the keen-eyed birdwatcher may spot a slightly different- looking bird hiding amongst them. Although very similar to its cousin in appearance, the Eurasian spoonbill can be distinguished by the lack of black skin between its eyes and bill. Some individuals may also have a yellow or orange spot at the end of their bills. It usually forages alone or in mixed flocks with the black-faced spoonbill and is, in Hong Kong, a much rarer species of spoonbill. However, globally it is widespread and is listed as a species of ‘Least Concern’ by the IUCN Red List (Tipper, 2016, p. 23; IUCN Red List, 2019).
Osprey (Pandion haliaetus): Distinguishable by its chocolate-brown and white plumage, this large raptor is a masterful and dramatic fisherman. When hunting, it will first hover high above the water, then drop out of the sky and plunge in feet first to grab a fish, which it will then carry away to eat elsewhere (Tipper, 2016, p. 31). When not hunting, it can commonly be seen sitting on stakes in shallow water or on other exposed perches (Viney et al, 2005, p. 64). It is largely a winter visitor to Hong Kong but a few individuals have shown behaviours indicating that they may one day breed here too, prompting WWF to build two artificial nest platforms in 2011 to further encourage them. However, for ospreys to have a long-term future at Mai Po, the threats of pollution and the climate crisis, both of which they are vulnerable to (WWF-Hong Kong, 2011), must also be adequately addressed.
Eurasian Otter (Lutra lutra): If there’s one native mammal that really stands to benefit from the protection of Mai Po, it’s the Eurasian otter. This semi-aquatic carnivore is found nowhere else in Hong Kong but Deep Bay and is supremely adapted to its wetland environment, possessing webbed feet for swimming, long whiskers to detect fish underwater, and a double layer of fur that waterproofs its skin and keeps it warm. It is a very playful, if largely solitary, animal, with both adults and juveniles play-chasing each other through the water. However, it is also secretive and nocturnal (Shek, 2006, p. 289–291) and so is rarely seen by humans. Despite its status as a protected species here, little information exists about the ecology of the Eurasian otter in Hong Kong that could help to protect it. Research by the University of Hong Kong is currently underway to fill these knowledge gaps, including determining habitat and resource use, potential threats and long-term population viability in Hong Kong (Environment and Conservation Fund, 2016).
Walk for Nature takes places on 7–8 November 2020 at Mai Po Nature Reserve, with the theme “Our Habitat, Our Home”, spotlighting the rich biodiversity of this Ramsar site.
References
· Environment and Conservation Fund, Approved Projects: Conservation action plan for Eurasian Otter (Lutra lutra) in Hong Kong: Assessment of threats and resource requirements, [website], 2016, https://www.ecf.gov.hk/en/approved/201668.html (Accessed: 11 July 2019).
· Hong Kong Wetland Park, Northern Shoveler, [website], 2019, https://www.wetlandpark.gov.hk/en/biodiversity/beauty-of-wetlands/wildlife/spatula-clypeata (Accessed: 12 July 2019).
· IUCN Red List, Eurasian Spoonbill, [website], 2019, https://www.iucnredlist.org/species/22697555/86435028 (Accessed: 30 July 2019).
· Shek, C.T. 2006. A field guide to the terrestrial mammals of Hong Kong, Agriculture, Fisheries and Conservation Department, Hong Kong SAR Government, Hong Kong. 289pp.-291pp.
· Tipper, R. 2016. A Naturalist’s Guide to the Birds of Hong Kong, John Beaufoy Publishing, United Kingdom. 23pp., 31pp., 41pp.
· 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. 48pp., 64pp., 82pp.
· WWF Hong Kong, WWF-Hong Kong aims high to attract nesting ospreys to Mai Po Nature Reserve, [website], 2011, https://www.wwf.org.hk/en/?5626/WWF-Hong-Kong-Aims-High-to-Attract-Nesting-Ospreys-to-Mai-Po-Nature-Reserve (Accessed: 11 July 2019).
