Decline In Wading Birds Indicates Deterioration Of Wetlands

Wetlands are rich yet fragile ecosystems teeming with life. Climate change, pollution, and human activities, however, have put these vital ecosystems at risk. Wading birds, like egrets and herons, play a crucial role in these habitats, and are natural indicators of environmental health. Their sensitivity to changes in water quality, pollution, vegetation, and prey availability makes them valuable for tracking ecosystem shifts.

To better understand the connections between environmental factors, fish diversity, and large waders in southwestern India, researchers conducted a decade-long study across 27 locations.

“Human activities have an immediate impact on wading bird populations. In contrast, climate change unfolds more gradually. A slight rise in water temperature each year may seem insignificant, but over a decade, the effects add up. That’s why long-term data is essential to understanding how climate-driven shifts impact species,” says K.M. Aarif, researcher in ecology at the Centre for Environment and Marine Studies, King Fahd University of Petroleum and Minerals, Saudi Arabia, and co-author of the study.

Comprehensive data

From 2010 to 2019, researchers observed how seasonal variations and environmental conditions influenced bird populations. The study covered estuaries, beaches, mudflats, mangroves, and agricultural landscapes, which are key feeding and breeding grounds for wading birds. Among the surveyed sites were the Azheekkal estuary, Ayikkara beach, Iringal estuary, Manthalakkadavu wetland, Vadakkumpad wetland, Vazhakkad agroecosystem, Kallampara inland mangroves, and KVCR mangroves and mudflats.

Six common bird species were monitored: the great egret, median egret, little egret, Indian pond heron, western reef heron, and black-headed ibis. Observations took place twice a month during early morning hours using binoculars and high-speed motion cameras. Birds were counted during low tide from designated scanning points, ensuring accurate and consistent data collection.

“Data collection is a challenging task, requiring patient and focused bird observation. Handling the vast datasets also poses difficulties. We overcame these challenges through the active involvement of our collaborators. They contributed data from diverse locations, and experienced field assistants provided crucial support for data collection,” says Aarif.

To assess habitat conditions, researchers conducted monthly analyses of water and sediment samples. They measured sediment variables such as salinity, pH, organic carbon, nitrogen, and phosphorus, alongside water variables such as salinity, pH, temperature, nitrate, and phosphate. Since fish are a primary food source for wading birds, fish populations were also monitored using net sampling methods.

“We selected these variables based on their known effects on organisms. For instance, nitrates generally promote phytoplankton growth. However, some species may proliferate more rapidly than others, leading to an overabundance of certain phytoplankton while others decline. The overall effect may be difficult to predict, but there is a trickle-down effect on zooplankton, benthic invertebrates and fish communities,” says Sabir Muzaffar, professor in the department of biology, College of Science, United Arab Emirates University, and study co-author.

To analyse trends over time, seasonal variations, and habitat differences, researchers used statistical models such as ANOVA, Generalised Linear Models (GLMs), and Structural Equation Models (SEMs). Researchers also examined which factors had the most impact on bird density and fish stock. Analysis was done using specialised software to find the best explanations for these patterns.

Declining waders

Over the ten-year study, researchers identified several significant environmental changes across the study area. Rainfall patterns became more inconsistent. Salinity, pH, and phosphorus levels increased in sediment, while organic carbon and nitrogen declined. Meanwhile, in water, temperature, salinity, and phosphate levels rose, whereas nitrate and chlorophyll-a (a measure of algae and cyanobacteria) decreased.

The densities of all wading bird species in the study sites declined significantly over a decade, from 2010 to 2019, with notable variations across seasons and habitats. Little egret, median egret, great egret, and Indian pond heron thrived in agroecosystems and estuaries but were less abundant in mudflats. Western reef herons were most common on beaches, while black-headed ibis preferred agroecosystems. Across all species, populations peaked post-monsoon and dropped during the monsoon season.

The results showed that multiple environmental factors shaped wading bird populations. Rainfall, sediment phosphorus, water nitrate, chlorophyll levels, and fish stock were major drivers, alongside sediment organic matter, water salinity, and pH levels. However, each species responded differently. For instance, while little and great egrets were negatively affected by rainfall, great egrets and reef herons benefited from sediment organic carbon.

Birds also varied in their ability to adapt. “Pond herons, often found in farmlands and city parks, have adapted to human-modified habitats and stressors,” says Muzaffar. “In contrast, western reef herons, which inhabit coastal areas, struggle to adjust to inland environments and face different stressors in their native habitats.”

Ultimately, the study linked the decline in large wading birds to environmental disruptions affecting their food supply. Rising salinity, temperature shifts, and nutrient imbalances impacted fish and plankton populations, making it harder for birds to find food. Additionally, overfishing and habitat destruction and modification further reduced available resources for these birds.

Restoring habitats

Safeguarding wading bird populations requires targeted conservation efforts. Restoring wetland habitats can improve nesting and foraging conditions, while sustainable fishing practices can help maintain stable fish stocks. Continuous monitoring is essential to track environmental changes and their effects on bird populations. Pollution control measures are also critical to preserving water and sediment quality.

“Anthropogenic pollutants, such as agricultural runoff and industrial discharge, must be better regulated to prevent long-term disruptions to nutrient cycles and food webs,” says Aarif. “Stronger government regulations are needed to control pollution and protect critical habitats for waders.”

The study highlights that the declining wading bird populations reflect a deeper ecological crisis in wetlands. Addressing this issue requires further research into coastal vegetation, phytoplankton, zooplankton, and fish diversity across seasons.

(Published under Creative Commons from Mongabay India. Read the original article here)