Managing Mai Po with Science
by Thomas Gomersall
When a wetland needs to be actively managed to meet the widely varying ecological requirements of 417 different bird species, not to mention 25 mammals, 21 reptiles, 54 fishes, 322 plants and over 1,000 invertebrates, the use of the best available science as a guide is essential.
One of the more recent examples of this at Mai Po Nature Reserve is the use of a study of reedbed bird communities to inform WWF’s management of this habitat. Although many songbird species, including globally threatened ones, use the reedbeds, their exact habitat requirements were historically poorly studied, making proper habitat management and determining their response to environmental change difficult. The latter was particularly concerning, as it meant that nobody knew how these birds would respond to parts of the reedbeds drying out due to a natural process of excess sedimentation and decomposing vegetation bolstering the soil body and raising it to above the water level.
To determine habitat use by reedbed birds at Mai Po, researchers compared the species diversity, abundance and types of birds in wet and dry reedbeds. To do this, WWF built a boardwalk through Mai Po’s largest reedbed stand, along which nets were set once to twice a week for three hours in the early morning during the autumn, winter and spring to (with AFCD approval) capture, record and release small birds in both types of reedbed.
The study found that while dry reedbeds supported more species that are habitat generalists, wet reedbeds supported a greater abundance of wetland-dependant species, with some being more than twice or thrice as abundant than in the dry reedbeds. Wet reedbeds were also more important for species of conservation concern like the threatened Manchurian reed warbler, which by some estimates has a smaller global population than the black-faced spoonbill.
“If we look at the relative abundance of this really critical species within the wet and dry reedbed, this was the species that showed the biggest preference for the wet reedbed,” says study co-author, Paul Leader. “By managing even a small part of Mai Po properly for this species, we can increase the carrying capacity here and potentially have a positive impact on its global population.”
Since the study’s completion, the last dry reedbed has been re-profiled and lowered by over 40 centimetres to create a new wet reedbed under deeper water. This science-based approach to habitat management is just one of many strategies outlined in Objective 1 of WWF’s new five-year (2019–2024) Mai Po Management Plan to maintain or increase populations of priority species. Like the previous five-year plan, its main priority is to monitor and conserve populations of migratory birds using tried-and-tested tactics like creating larger water bodies for ducks and draining gei wai to provide feeding habitats for waders. But it will also introduce new actions to protect resident birds, mammals, reptiles and insects, as well as help Mai Po adapt to climate change.
As with everything WWF does, these new conservation actions will be guided by science. For several of the priority species at Mai Po, like the Eurasian otter, bent-winged firefly, Reeves’ terrapin and Chinese soft-shelled turtle, basic ecological and demographic information vital for successful conservation is currently lacking. Population and distribution surveys for these species will help to fill these knowledge gaps and allow WWF to devise appropriate strategies to conserve them. Similarly, surveys will be used to identify threats outside of the reserve to species that leave it to forage, like the endangered collared crow.
“What happens around Mai Po will affect the [crow] population that uses Mai Po as a roosting site. For example, development can affect their feeding sites and if they lose their feeding sites, the population can decline,” says Eric Wikramanayake, WWF-Hong Kong Director of Wildlife and Wetlands. “So we need to find out where they’re foraging and what’s happening to those kinds of habitat.”
Climate science is already proving instrumental for informing conservation plans. Under projected sea-level rise scenarios, parts of the reserve will eventually be flooded, including the mudflats that are an important feeding habitat for many bird species. Fortunately, climate models have also found that fishponds could be used to create alternative habitats and act as buffers against climate change impacts, making protecting them from development all the more important.
But in order to effectively protect Mai Po’s migratory birds, other wetlands along the East Asian Australasian Flyway (EAAF) that these species use must also be protected. For years, WWF-Hong Kong has been sharing its science-based approaches to protecting and managing Mai Po with wetland managers in the northern part of the flyway in China, Korea and Japan. Now, as it takes on the leadership role in WWF’s Asian Flyway Initiative; it will be able to do so with wetland managers across the whole EAAF as well as provide training and advice, empower greater co-operation between all EAAF regions and identify important sites for migratory birds.
