Over ten years, researchers have tracked the health of Kerala’s coastal ecosystems by monitoring six species of large wading birds, including the Great Egret, Indian Pond Heron, and Oriental White Ibis. These birds, which depend on wetlands and estuaries for survival, are now struggling to adapt to disappearing food sources and degraded habitats.
A comprehensive decadal study conducted between 2010 and 2019 by K. M. Aarif and an international research team covered 27 wetland sites across estuaries, mangroves, beaches, mudflats, and agro-ecosystems in southwestern India. The research draws a sombre picture of these birds’ declining populations and the cascading ecological changes behind it.
What waders reveal about ecosystem health
Wading birds are apex indicators of wetland health. Their feeding habits, especially their reliance on fish and invertebrates, make them particularly sensitive to disruptions in food chains. What we see is a rapid deterioration of entire aquatic ecosystems.
Employing rigorous monthly monitoring, the team tracked population densities of six prominent wading bird species and measured a host of environmental variables, including water salinity, nitrate levels, sediment composition, rainfall, temperature, and chlorophyll concentration, a proxy for aquatic productivity.
The findings were alarming. The population densities of all six studied species declined significantly over the decade. This decline mirrors the degradation of the ecosystems that support them with falling primary productivity, dwindling fish stocks, increased water and sediment salinity, rising phosphorus levels, and erratic rainfall.
Water chemistry and climate woes
The study presents alarming changes in water and sediment chemistry. Over the years, water temperature, salinity, pH, and phosphate levels all showed significant increases, while nitrate and chlorophyll levels declined. In the sediments, salinity, pH, and phosphorus rose, while nitrogen and organic carbon decreased.
These chemical shifts are more than just numbers. They point to increasing eutrophication, a process often driven by fertiliser runoff from agriculture. The study notes that sediment phosphorus had a consistent and negative effect on all six bird species — reducing chlorophyll levels, decreasing fish stocks, and thereby contributing to population declines.
Meanwhile, rainfall — the seasonal lifeblood of wetlands — became more erratic. It turned out to be a double-edged sword. On one hand, rainfall helped boost primary productivity by bringing in nutrients. On the other, excessive rainfall during monsoons diluted nutrient concentrations and washed them away too quickly, undermining the food base before it could stabilise.
Increased water temperatures — potentially linked to broader climatic changes — added yet another stressor. Elevated temperatures can destabilise planktonic food webs, increase metabolic stress on aquatic species, and shift the balance of prey availability, all of which affect bird foraging success.
Species-specific struggles
Each of the six wader species studied responded differently to these environmental stressors:
Great Egret populations declined with increasing rainfall and nutrient imbalance.
Median Egret suffered in areas with high salinity, phosphorous and excess nitrogen.
The Western Reef Heron showed temporary gains in high-salinity zones, benefiting from sediment carbon and salinity, but declined overall.
The Indian Pond Heron responded positively to phosphates but was still vulnerable to rainfall changes.
Oriental White Ibis displayed some resilience in estuarine and farm ecosystems but faced overall decline.
The seasonal pattern was also telling: all six species peaked in density post-monsoon and were lowest during the monsoon season. “This suggests that changing monsoon patterns and rainfall regimes directly impact the foraging success and habitat availability for these birds,” explained the report.
Adaptation or last refuge?
With natural habitats collapsing, many birds have turned to human-dominated landscapes. Estuaries and agroecosystems, particularly post-monsoon, emerged as the last refuges for these birds particularly after the monsoon.
However, this shift is not necessarily positive. Rice paddies, while historically functioning as surrogate wetlands, are becoming less viable due to pesticide use and shifts in irrigation practices. Chemical pollution also poses bioaccumulation risks, threatening long-term bird health. Pesticides can reduce the abundance of invertebrates and small fish, eliminating what little feeding opportunity that remains.
Moreover, the contamination of wetlands by heavy metals and excessive inorganic nutrients—another by-product of intensified agriculture and industrial discharge—poses serious bioaccumulation risks to these sentinel species. Previous studies by Aarif et al. (2023, 2025) have already flagged heavy metal biomagnification in similar ecosystems.
A grim forecast
The evidence is unequivocal. What we’re witnessing is not just a local ecological shift, but a symptom of global trends in wetland degradation. The long-term decline in chlorophyll, fish biomass, and wader populations observed in southwestern India echoes similar findings from East Asia, North America, and Europe.
As India intensifies its development along coastlines and inland river systems, these ecosystems face increased stress. And while wetland restoration efforts and protected area declarations have made sporadic progress, they are no match for the relentless pace of degradation documented here.
The way forward
The authors urge targeted conservation measures. “We need to reduce nutrient runoff, control salinity intrusions, and improve the resilience of wetland habitats,” said the paper. Long-term monitoring must become central to environmental policy. In particular, tracking sediment and water chemistry — not just surface biodiversity — can offer early warning signs of ecological collapse.
Policy should also recognise the multifunctional role of agroecosystems. If managed sustainably, rice paddies and semi-natural farms could serve as critical secondary habitats. But that would require regulations around pesticide use, water management, and perhaps even incentives for eco-sensitive farming.
Above all, this study is a call to view wading birds not merely as picturesque symbols of nature, but as frontline indicators of wetland health. Their presence — or absence — tells a story of water, soil, food, and climate. And right now, that story is one of distress.
As these birds disappear from our skies, it’s not just their cries we’re losing. We may be silencing the last warnings of ecosystems in crisis.