Issues Magazine

Waterbirds at Risk at Bundala RAMSAR Site

By Maria Grazia Bellio and Richard Kingsford

Irrigation projects upstream have left some wetlands high and dry while others are flooded, with consequences for the waterbirds that depend on them.

Waterbirds are wetland-dependent birds, and a key component of wetlands. Sadly, waterbird populations around the world have declined dramatically in recent decades, with degradation and alteration of wetland habitat occurring as a result of agricultural expansion and development activities, particularly in Asia.

Bundala National Park in the south-east of Sri Lanka was listed as a RAMSAR site in 1991 due to its significance as a habitat for waterbirds, in particular migratory shorebirds of the Central Asian Flyway. In the past two decades, however, agricultural expansion upstream of the RAMSAR site has modified the hydrology of the RAMSAR wetlands. Other pressures, such as invasive plant species and pollution from fertilisers used in agriculture, have altered and deteriorated the environmental integrity of the Bundala lagoons.

Although agriculture, and irrigated agriculture in particular, have been critical in supplying the food needs of an ever-increasing human population, the conversion or drainage of wetlands for agricultural development, altered hydrological cycles, and pollution resulting from the use of fertilisers have been the principal causes of inland wetland loss and habitat degradation worldwide.

Water regime modification has permanently flooded some wetlands while many wetlands are permanently drier. It has also reduced the diversity of wetlands in the landscape.

Manipulating the water regime of wetlands has ecological consequences. For many waterbird species, wetlands become more productive when they are shallow as their potential as a hunting habitat increases significantly. If we aim to maintain the diversity of wetland communities, we need to understand the effects of water regime changes on the survival and composition of different species of flora and fauna.

Causes and drivers for the decline of most waterbird populations in Asian countries remain unclear. For example, some shorebird populations of the Central Asian Flyway have declined by over 70% at one of the main wintering grounds for shorebirds along the east coast of India, but potential threats have not been quantified. Knowledge of waterbird ecology of the Central Asian Flyway is particularly poorly known, even though the flyway has the greatest number of globally threatened waterbirds.

A PhD project was started in 2006 as a joint collaboration between the University of NSW, the International Water Management Institute and the Department of Zoology of the University of Colombo, Sri Lanka. The project assessed the effects and potential impacts of hydrological changes on waterbirds and their habitats at two of lagoons in Bundala National Park. These changes have occurred as a result of agricultural expansion in the Kirindi Oya settlement area. Research examined the waterbird responses to cycles of flooding and drying in wetlands in order to determine what happens to the waterbird community when these cycles are modified or disrupted by irrigated agriculture. Mechanisms that regulate and drive resource use, including habitat selection, spatial distribution and heterogeneity of waterbird habitat, from broad landscape-scale within the basin through the local scale to the within-habitat fine microscale have been investigated.

The results have shown that agriculture detrimentally affect the waterbird community, in particular shorebird species of the Central Asian Flyway, of one of the Embilikala lagoon of the RAMSAR site. Impacts on the natural lagoon of Embilikala encompass hydrological disruption of the natural cycle of flooding and drying, increased water turbidity and decreased salinity levels.

These impacts directly affect the waterbird communities of the RAMSAR site through changes in the abundance and composition of the key food resources they depend on. This is particularly true for shorebird species that depend on the availability of shallow areas for feeding and an abundance of specific prey.

Mitigation actions for waterbird conservation at Embilikala need to restore appropriate hydrological regimes that in turn will influence the availability of physical habitat (water depth) and food resources suitable for waterbirds. Currently, at the catchment scale, the only alternative for migratory shorebirds is to use artificial wetlands (e.g. irrigation reservoirs, rice paddies, salt evaporation ponds), but these are not functionally ecological equivalents to natural wetlands. However, artificial wetlands may be managed to provide habitat for waterbirds.

Opportunities therefore exist to restore the functionality of the natural wetlands of the RAMSAR site as well as to manage artificial wetlands for waterbird conservation.

Managing wetlands for waterbird conservation may also bring benefits to many other ecosystem services (e.g. food provisioning, access to freshwater, fisheries, tourism) that these wetlands provide to people’s livelihoods.