Birds are recognised as the most important indicators of health of an ecosystem. Therefore, a declining avian population points to the loss of biodiversity. The staggering drop in the number of birds in various parts of Kerala that came to light in the Asian Waterbird Census (AWC) conducted recently is a warning that the ecosystem is not in the pink of health.
A survey conducted in the Thrissur-Ponnani kole fields, a Ramsar site known for the number and diversity of birds, on the first day of 2023 recorded the lowest count of waterbirds in three decades here. Kole wetlands, spread over an area of 13,632 hectares straddling Thrissur and Malappuram districts, have been visited by hundreds of migratory birds every year.
A total of 9,904 birds belonging to 90 different species were counted this year, while the counts were 16,634 & 15,956 in 2021 and 2022 respectively. There has been a marked decline in the number since 2018, when the count was 33,499.
Loss and degradation of natural habitats, changes in land use patterns and indiscriminate use of pesticides are the major drivers of the drop in avian population in addition to the vagaries of climate change, says P.O. Nameer, Head of the Centre for Wildlife Studies, College of Forestry, Kerala Agricultural University, Thrissur, who coordinated the survey.
Roads, concrete bunds
“There are many drastic changes happening in the kole fields, which is a dynamic wetland ecosystem. Over the years, the annual one-season cultivation system (oruppoo) has made way to a two-season (iruppoo) system. Huge machinery has been introduced to mechanise farming. In the name of improving facilities for farmers, the muddy bunds have been replaced by concrete bunds. Crisscrossing the fields, many roads have come up. Concrete bund roads were constructed for transporting the farm machinery. Entire hydrology of the kole field was drastically changed. Increased human intervention, including dredging using earthmovers, lorries and tarring of roads, may have hit the arrival of birds,” he notes.
The sedges and grasses on the sides of muddy bunds have been the breeding spots of many birds. They make their nests amidst the grasses. When concrete bunds were set up, they lost their nesting places. Indiscriminate use of pesticides killed their prey, which are insects, frogs, water plants, some weeds and microorganisms.
Dr. Nameer pointed out that disinfection of fields ahead of fish farming, which was introduced about 10 years ago to increase farmers’ income, too, adversely impacted the health of the ecosystem.
Lack of food, breeding ground
These human interventions must have discouraged the migratory birds. Add to that the shortage of food and loss of breeding ground, they would’ve migrated to better places. However, this cannot be stated without proper studies, Dr. Nameer says.
Meanwhile, farmers put the blame on indiscriminate dumping of waste in the kole fields which they argue is on the rise at an alarming rate. Hostels, hotels, hospitals and septic tank cleaners use it as a place to discard waste mostly during nighttime.
Invasive species strike
Increasing invasion of alien species can also have a negative impact on the ecosystem in the kole fields, says Prem Das, Research Scholar at the Kerala Forest Research Institute, Peechi, who is conducting studies on invasive species.
“Trees along the bunds in kole fields are infested by the invasive alien climber, Mikania micrantha, which is popularly known as mile-a-minute weed. The infestation will lead to the drying of the tree. The fast-spreading climber is capable of destroying perching sites for birds.” The terrestrial alien species reduces the foraging area for birds, especially for raptors and other fish-hunters.
Studies suggest that there are five aquatic invasive plants and 10 terrestrial invasive plants in the kole wetlands. While water hyacinth, salvinia (african payal), water spinach, red cabomba and yellow burhead are the aquatic invasive plants, Singapore daisy, Mikania micrantha (Dhritharashtra pacha), metal weed and mission grass are the common terrestrial plants.
During each rainy season, these species spread widely. Places where agriculture is not done regularly have been filled with them. The aquatic invasive plants, which cover the water surface, prevents penetration of light in the water, thereby reducing the availability of oxygen and preventing the growth of aquatic organisms, a major source of food for the kole birds.
Along the bunds, the native vegetation has been displaced by invasive varieties making it difficult for many bird species to breed. However, such invasive plants help some species, points out Mr. Das. For example, Purple Moorhen (Neelakkozhi) has found a perfect hiding place in the Limnocharis flava (yellow burhead), an invasive plant, which is semiaquatic.
How birds help
Experts say that the decline in the number of birds in the wetland ecosystem will destabilise and ruin it. To cite an example, when bird droppings nurture the fields, it induces activities of many organisms in the water including fish. Many birds eat insects, herbs, pests and weeds, helping farming. Others facilitate pollination. The loss of habitat of birds portends a gloomy future for this fecund ecosystem.