Waterbirds, indicators of wetland health

Wetlands are unique, complex and sensitive habitats that form a connection between terrestrial and aquatic ecosystems and provide a range of ecosystem services to humans. They are equally crucial for the survival of birds and provide critical foraging, roosting, nesting, chick-rearing, moulting, stop-over and wintering habitat for migratory and resident waterbirds.

Waterbirds are regarded as indicators of wetland ecosystem health because they strongly influence the diversity of organisms living in the water bodies and form an important part of the food web informs this paper titled 'Long-term anthropogenic stressors cause declines in kingfisher assemblages in wetlands in southwestern India' published in Ecological Indicators.

Waterbirds such as Kingfishers play an important role in sustaining the integrity of wetland ecosystems and depend on wetlands for their food consisting of mainly fish and also frogs, reptiles, caterpillars, insects, molluscs and crabs and can be useful indicators for assessing the health of wetland ecosystems. 

Declining kingfishers can be an indication of declining ecosystem quality while a healthy kingfisher population could indicate a healthy wetland ecosystem thriving with plants and animals, both small and large forming a crucial component of the food web supporting the survival of the wetland ecology.

Impact of wetland pollution on waterbirds

Anthropogenic pressures on coastal and inland wetlands are increasing in India with large amounts of agricultural chemicals, municipal pollution and industrial wastes being deposited into wetlands, causing irreversible changes in these aquatic systems. Long-term studies on birds can greatly help in understanding the health status of the habitat and for helping in designing and implementing effective management strategies.

Very few studies have looked at the impact of poor water quality on birds and very few studies exist on the relationships between poor wetland status and the impact of poor water quality on Kingfisher survival in India. The paper discusses the findings of  study that looked at the abundance of five species of Kingfishers across five different wetland habitats in Kerala, and the southwest coast of India and evaluated the impacts of environmental variables such as air temperature, water temperature, humidity, turbidity, organic waste on the wetlands and kingfisher abundance in the region. 

A total of five sites were selected, namely Mavoor wetland, Vazhakkad agroecosystem, Kallampara mangroves, Vadakkumpad mangroves and Kadalundi- Vallikkunnu Community Reserve (KVCR) mangroves. The most commonly available kingfisher species such as Common Kingfisher, White-throated Kingfisher, Pied Kingfisher, Stork-billed Kingfisher and Black-capped Kingfisher were selected for the study. 

Findings

The study found that Kingfishers across different wetland habitats declined. This had to do with the deteriorating water quality of the wetlands due to anthropogenic disturbances, increasing rate of urbanisation and human activities such as agricultural practices, untreated waste disposal and unsustainable fishing practices.

Vadakkumpad mangroves showed least decline in kingfisher abundance as the site had been exposed to the least anthropogenic disturbances. Common Kingfisher or Small blue Kingfisher, White-throated Kingfisher, Pied Kingfisher, Black-capped Kingfisher and Stork-billed Kingfisher were documented from KVCR mangroves, Kallampara mangroves, Vadakkumpad mangroves and Mavoor wetland. In contrast, Vazhakkad agro-ecosystem supported only four species of kingfishers namely Common Kingfisher, White-throated Kingfisher, Pied Kingfisher and Stork-billed Kingfisher. 

The study found a significant increase in air temperature, water temperature and turbidity and a decrease in humidity across the mangrove sites. Increase in air temperature resulted in gradual increase in water temperature and influenced water quality through alterations in pH, dissolved oxygen content of the water, in addition to anthropogenic influences such as agricultural run-off, domestic and industrial waste disposal, microplastic and heavy metal contamination. These adversely affected fish residing in the waters and thus the survival of waterbirds near the water bodies. 

Increase in turbidity of wetland waters was also found to have a negative influence on the abundance of kingfishers due to their inability to see and catch fish from the waters. Kingfishers detect moving prey more efficiently in clear or less turbid waters. Increased suspended solid particles restrict light penetration, reducing the visual range over which prey can be sighted. This could diminish their foraging efficiency. Light dependent bottom-dwelling aquatic organisms are severely affected by the attenuation of the light and are sensitive to the increased temperature developed on the absorption of heat by the suspended solid particles. 

Some species of kingfishers appeared to be declining faster than others. This can be due to the variation in food available in different wetland ecosystems, type of the wetland, vulnerability to predation, and response to climatic changes. For example, in the study, it was found that the Pied Kingfisher was declining at a faster rate while White-throated Kingfisher declined at a slower rate. Pied Kingfisher mainly preys on fish by diving from a perch or diving after hovering and could be more prone to be affected by decline in fish availability compared to other species. In comparison, the Whitethroated Kingfisher is voracious and feeds on almost all prey (such as insects, worms and other invertebrates, frogs, perching birds and fish) that they encounter and hence could be less affected by fish depletion. 

The study found that the Pied Kingfisher had disappeared from KVCR as it had been experiencing significant environmental change and decline in water quality which altered the presence of small and large animals (zooplankton) living in the waters that are an important part of the food web and crucial as food for fish that reside in the waters. 

The study sites were severely polluted with both organic and inorganic wastes like poultry and slaughter wastes, plastics and broken glass. Domestic wastes disposed in the wetlands attracted a large number of predatory birds that, in turn, drove away the kingfishers.

Urgent wetland conservation plans are needed

The disturbances in the wetland environment, which led to a decline in the presence of waterbirds such as Kingfishers with local extinction of Pied Kingfisher from one of the study sites, and the current IUCN status (VU) of Black-capped Kingfisher highlight the urgent need for immediate implementation of sustainable habitat and species specific conservation plans.

The study argues for the need to:

• Conduct an investigation on the population and abundance of other species of organisms and biodiversity shifts in the wetlands to better understand the impacts of envioemntal and anthropogenic factors on wetlands to help formulate conservation strategies to ensure long-term sustainability of wetlands. 
• A review of the waste disposal practices and an assessment of habitat quality of these wetlands to undertake urgent clean-up and remediation actions to help improve wetland habitat quality and restore the biodiversity of the region.