Mai Po Biodiversity: Mudflats

by Thomas Gomersall

Separating Hong Kong’s nature reserve from Shenzhen, the coastal mudflats of Mai Po with their wealth of mudskippers, crabs, shrimps and other aquatic organisms are a smorgasbord for many of the migratory water birds that visit or pass through Deep Bay. The mudflats play host to the ubiquitous avocets, herons and black-faced spoonbills, but are also an important feeding and resting ground for plenty of other birds that can only be seen here, some of them critically endangered.

Unfortunately, the prime conditions that draw water birds to this site are under threat. A combination of natural sediments from the Pearl River and sediments artificially created by coastal development in Shenzhen has led to an unnaturally large sediment load being trapped by the roots of mangrove trees. The excess sediment gradually builds up and stabilises into solid ground, shrinking the mudflat habitat further and faster than it would naturally. For more details on WWF’s work to combat this, see my blog on the Mai Po Mudflats eco-visit.

Photo credit: Thomas Gomersall

Blue-Spotted Mudskipper (Boleophthalmus pectinirostris): If there’s any one animal that could be described as the lifeblood of the mudflats, it has to be the blue-spotted mudskipper. This bizarre amphibious fish is a staple food source for many of the water birds that flock here and is so numerous that the mud can almost seem alive with tiny, wriggling bodies that can be highly entertaining for wildlife watchers. For instance, the males are prone to dramatic territorial and mating displays, which include facing each other head-on and raising their dorsal fins as a threat or to advertise themselves to females (Fong et al, 2005, p. 69).

Photo credit: Martin Hale

Grey Plover (Pluvialis squatarola): The grey plover can be confused with the similar-looking Pacific golden plover (Pluvialis fulva), but is larger and greyer with a bigger head and beak. It is one of the most common birds on the mudflats, gathering here in small groups (Viney et al, 2005, p. 90). It uses a feeding technique common to plovers called the run-stop-peck technique, in which it will run from place to place, catching any prey it finds at the places it stops at (Tipper, 2016, p. 44). While it may look very plain during the period when it’s in Hong Kong, towards the end of its time here, it adopts an attractive black-and-white breeding plumage (Viney et al, 2005, p. 90).

Photo credit: Martin Hale

Spoon-billed Sandpiper (Eurynorhynchus pygmaeus): From one of the most common mudflat birds to one of the rarest. The only species of sandpiper with a spoon-shaped bill, the charismatic spoon-billed sandpiper is a passage migrant in Hong Kong, stopping here to rest and feed en-route from its breeding grounds in the Northeast Asian tundra to its wintering grounds in Myanmar and the Bay of Bengal (Williams, 2016). And of the many birds here that are threatened by habitat loss to coastal development, it is probably the species for which immediate, concerted conservation action is most urgently needed. The spoon-billed sandpiper has extremely specific habitat requirements; feeding grounds must not be too muddy or too sandy and must have silt that is just the right consistency for its small beak to plow through in search of small invertebrates. Naturally, this severely restricts the number of suitable feeding grounds along its migration route, several of which have now been destroyed. Combined with hunting in Myanmar and other areas, this has crashed the sandpiper’s numbers from 1,000 breeding pairs at the start of the century to just around 100 today (Williams, 2018). In the face of such a dire situation, the protection of mudflats like those of Deep Bay is truly a matter of life and death for this sparrow-sized shorebird.

Photo credit: Martin Hale

Eurasian Curlew (Numenius arquata): Being a feeding ground for avocets, black-faced spoonbills and spoon-billed sandpipers, the mudflats certainly have their fair share of birds with odd-looking beaks, another one of which is the Eurasian curlew. Named for its melodious ‘coor-lee’ call, the curlew also possesses an extraordinarily long curved beak, which it uses to probe for worms, mollusks and other invertebrates (Tipper, 2016, p. 51; ICUN Red List, 2019). During the winter, this bird is heavily dependent on coastal mudflats for feeding, making it very vulnerable to coastal development. Illegal hunting is another problem it faces, as it has been known to get caught in nets set for migrating shorebirds in mainland China (IUCN Red List, 2019; WWF-Hong Kong, 2013)

Photo credit: Thomas Gomersall

Spotted Redshank (Tringa erythropus): It may look very similar to the common redshank (Tringa totanus), but the spotted redshank does have some very unique characteristics of its own. For one thing, it has a longer bill and legs than the common redshank and does not have the same white bars visible on its wings during flight. Its smoky-black breeding plumage is also drastically different from that of other birds of this group. But appearances aren’t everything with this bird. Unlike most shorebirds, which feed exclusively by wading through the shallows, the spotted redshank will also swim to find food and regularly does so (Viney et al, 2005, p. 98; Tipper, 2016, p. 52; Allcock, 2019) — a useful adaptation in a world of constantly changing tides.

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

· Allcock, J., interviewed by Thomas Gomersall, 2019, WWF-Hong Kong Birdwatching Society.

· Fong, T.C.W, Lai V.C.S and H.T.H. Lui. 2005. Photographic Guide Series of Hong Kong Nature (2): Estuarine Organisms — Mangrove, Mudflat and Seagrass Bed. Jan KC Chan, HK Discovery Limited, Hong Kong. 69pp.

· IUCN Red List, Eurasian Curlew, [website], 2019, https://www.iucnredlist.org/species/22693190/117917038 (Accessed: 1 August 2019).

· Tipper, R. 2016. A Naturalist’s Guide to the Birds of Hong Kong, John Beaufoy Publishing, United Kingdom. 44pp., 51pp., 52pp.

· 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. 90pp., 98pp.

· Williams, M. ‘How Hong Kong birdwatchers helped save wetlands icon the black-faced spoonbill’. South China Morning Post, 4 May 2016, https://www.scmp.com/magazines/post-magazine/article/1941086/how-hong-kong-birdwatchers-helped-save-wetlands-icon-black (Accessed: 27 August 2019).

· Williams, M. ‘One in 10 Hong Kong bird species at risk of extinction: can they be saved’. South China Morning Post, 18 May 2018, https://www.scmp.com/magazines/post-magazine/article/1941086/how-hong-kong-birdwatchers-helped-save-wetlands-icon-black (Accessed: 27 August 2019).

· WWF-Hong Kong, Endangered Eurasian curlew caught in Bohai Bay, China, [website], 2013 https://www.wwf.org.hk/en/?9360/ (Accessed 1 August 2019).

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