Breeding Black-winged Stilts
by Thomas Gomersall
While a few bird species breed at Mai Po Nature Reserve or have shown signs of one day doing so, the majority of species that visit Mai Po do so exclusively for the purposes of feeding and resting during the winter. In recent years, WWF has been making considerable efforts towards making the reserve an attractive breeding ground, including for one of its most common waterbirds, the black-winged stilt (Himantopus himantopus).
Instantly recognisable from its plumage colour and extraordinarily long legs — measuring over half the length of its body — the black-winged stilt is largely a passage migrant and winter visitor to Hong Kong. But in 2003, six pairs made the unprecedented move of staying behind for the summer to breed at Mai Po. By 2007, that number had increased dramatically to more than 31 pairs.
It is not entirely clear why the birds suddenly started breeding here, though it may be part of a climate change-driven expansion of their breeding range in South and Southeast Asia. But the fact that they were able to do so successfully has a lot to do with Mai Po’s habitat management programme.
Prior to 2003, WWF converted several brackish-water fishponds into shallow freshwater habitats and created several shallow islands in them. Though not created specifically to benefit black-winged stilts, the open islands with their muddy substrates proved to be ideal nesting sites, while the freshwater ponds provided habitats for the aquatic invertebrates that birds need to feed their chicks with.
Recognising the importance of these habitats for breeding black-winged stilts, WWF set about creating more of them, constructing new islands within Gei wai 21 in 2009 and maintaining freshwater habitats within the reserve. As a result, black-winged stilts have nested at Mai Po for nearly every consecutive year since records began in 2007 (with more than 58 pairs in 2011). Today, the reserve is one of only two breeding sites for them in Hong Kong and the most important of those two.
For WWF, the use of Mai Po as a breeding ground by black-winged stilts also provides an opportunity to learn more about their life history and migration behaviour. When they are large enough, chicks are captured and ringed with their own unique leg tags, which are colour-coded according to the location they were first tagged in (white and yellow for Hong Kong). Later, researchers and birdwatchers in Hong Kong and elsewhere can use these tags to obtain valuable information about them
“It allows [them] to identify individuals that are born in Mai Po and in the long run, the re-sighting record could tell us whether they come back here to breed, how far they migrate and how old they could live to be,” says Carmen Or, Assistant Manager of Mai Po Nature Reserve’s research and monitoring team.
But while climate change may have played some role in driving the black-winged stilts to nest at Mai Po, it now threatens to play an even larger one in destroying their new breeding grounds. Due to their shallow topography, the islands are prone to flooding by sudden heavy rainstorms and as these become more common with the changing climate, there is concern that nests could become even more susceptible to flooding. To combat this, WWF-Hong Kong aims to use floating breeding platforms to allow the black-winged stilts to continue nesting here in the future, with help from some obliging young people.
In 2019, seeing an opportunity to empower young people in wetland conservation, WWF’s One Planet Youth (OPY) programme teamed up with its Mai Po team to create an OPY project working on the breeding platforms. Participants will be provided with the training and field skills needed to design, build and install the platforms in the field, then to monitor their usage by black-winged stilts and their impacts on other wildlife.
Work on the breeding platform project has been indefinitely delayed due to the COVID-19 pandemic. But early indications have been promising. Schools that the OPY leaders have shopped the project around to have shown strong interest, with one even integrating it into their next year’s syllabus.
With luck, the pandemic will have subsided and the project can go ahead. For the time being, Mai Po’s breeding black-winged stilts seem to be doing fine on their own. And with the autumn migration season not far away, it shouldn’t be long before they are joined by many others.