- Migratory birds are losing critical stopover habitats across South Asia along major global flyways due to human-driven causes.
- Draining wetlands and overfishing eliminate aquatic vegetation, invertebrates and fish that form the dietary base for migratory birds.
- Researchers emphasize that protecting migratory birds requires coordinated action beyond national borders.
Every winter, millions of birds fly thousands of kilometers via the Central Asian Flyway (CAF) and East Asian-Australasian Flyway (EAAF), from the frozen expanses of Siberia and Central Asia to the warmer South Asia and beyond.
The birds’ migration depends on a chain of intact ecosystems: primarily wetlands, riverine forests and coastal mangroves, which serve as their crucial stopover sites for rest and refueling.
However, today, many of these habitats and food sources are disappearing.
Researchers from Bangladesh, Nepal, Pakistan, India, the Maldives, Bhutan and Sri Lanka have assessed that wetland conversion amid agricultural expansion and rapid urbanization, unplanned fishing and pollution are degrading the wetlands, mudflats and river systems across South Asia.
Bangladeshi ornithologist Sayam U. Chowdhury, a researcher at the Conservation Research Institute (CRI) under the University of Cambridge, explains how rapid urbanization and the loss of natural wetlands pose a serious threat to migratory waterbirds.
Although many people associate waterbirds with fish, most migratory species — including ducks, geese and shorebirds — rely on shallow wetlands, mudflats and nearby agricultural lands. They primarily feed on aquatic vegetation, seeds and invertebrates rather than fish.
“When waterbodies are drained, polluted or heavily altered, it destroys the habitats and food resources these birds depend on during their non-breeding season,” Chowdhury tells Mongabay.
Bangladesh lies within both the Central Asian and the East Asian-Australian flyways and provides habitat for around 310 migratory bird species, according to Bangladesh’s National Report of COP13’s Convention on the Conservation of Migratory Species of Wild Animals. However, Chowdhury says that the latest assessment suggests that around 400 migratory bird species visit Bangladesh.
These include globally threatened and vulnerable species such as the spoon-billed sandpiper (Calidris pygmaea), Nordmann’s greenshank (Tringa guttifer), Baer’s pochard (Aythya baeri) and greater spotted eagle (Clanga clanga), according to the IUCN Red List of Bangladesh.
According to Chowdhury, unplanned development, agriculture and aquaculture expansion, cultivation of new crops such as watermelon, use of pesticides, conversion of coastal wetlands into saltpans and shrimp farms, mangrove plantation on mudflats, hunting and pollution are among the major threats to the migratory birds along Bangladesh’s coastal wetlands.
A regional crisis along the Central Asian Flyway
According to Central Asian Flyway Situation Analysis (2023), many parts of the flyway region, spanning 30 countries across North, Central and South Asia and Trans-Caucasus, are witnessing waterbird declines as expanding human settlements alter and fragment habitats.
More than 600 migratory bird species use the CAF.
South Asian country Pakistan sits at the heart of the CAF. In 2021, WWF-Pakistan called for the protection of migratory birds.
Zulfiqar Ali, a professor at the Institute of Zoology of the University of the Punjab, Pakistan, assessed that wading birds, such as the charismatic black-tailed godwit (Limosa limosa) and the Eurasian curlew (Numenius arquata), which probe soft mud for invertebrates, are particularly vulnerable to the draining and siltation of wetlands in Pakistan.
Similarly, raptors, including the Steppe eagle (Aquila nipalensis), suffer from the decline in rodent and small bird populations in degraded grasslands and agricultural areas, Ali says, blaming illegal hunting and trapping, conversion of natural floodplains to monoculture crops, and overfishing in lakes and rivers for the degradation of the waterbird habitat.
Overfishing has caused prey shortages and declines in fish-eating birds such as black-bellied terns (Sterna acuticauda) and Indian skimmers at the Ramsar-listed Koshi Tappu in Nepal over the past decade, according to a study published in 2024.
Co-author of the study, renowned Nepali ornithologist Hem Sagar Baral, says, “The most affected are the species of wetland birds where we have evidence that fish stock has declined and therefore bird species that depend on fish as their major diet have suffered.”
Baral also expresses concern about Pallas’s fish eagle (Haliaeetus leucoryphus) which, he says, may have even bred in Nepal during winters but now they are a non-breeding winter visitor to the country.
Researchers in Bhutan identified overfishing in Mochu and Phochu rivers, crossing the Jigme Dorji National Park, as the major reason for the critically endangered white-bellied heron (Ardea insignis) losing prey, according to a study published in 2021.
Some Indian researchers, assessing the situation of 82 migratory bird species in three sanctuaries — the Bhindawas Bird Sanctuary, the Sultanpur National Park and the Keoladeo National Park — identified habitat degradation and fragmentation, excessive tourist presence, and improper management of food for birds as the threats, according to a study published in December 2024.
Another study, published in February 2025, traces that wetlands, mudflats and coastal areas in the Maldives are being drained or altered for agriculture, tourism and urban expansion, which makes the coastal country inhospitable for wader species, like sociable lapwing (Vanellus gregarius), curlew sandpiper (Calidris ferruginea) and black-tailed godwit.
High-quality natural habitats are crucial
Chowdhury points out that, in Bangladesh, inland wetlands are often managed mainly for fisheries, with practices like water level control and vegetation removal that degrade habitats for ducks, geese and waders. Meanwhile, on the coast, land reclamation and aquaculture have destroyed large areas of tidal flats, vital for shorebirds.
Zulfiqar observes that the iconic sites like the Ramsar site Indus Delta, once a sprawling labyrinth of mangroves and creeks, have severely shrunk due to upstream dams and sea intrusion, while inland freshwater lakes are being drained for farmland or polluted by industrial and agricultural runoff.
Elaborating how this physical destruction of habitat is causing food shortage, he says, “The very act of draining a wetland eliminates the submerged aquatic vegetation, invertebrates, fish and amphibians that form the dietary foundation for diverse [bird] species from ducks and geese to waders and raptors.”
“Consequently,” Zulfiqar adds, “birds arriving after grueling, nonstop flights over mountains and deserts find their traditional stopovers either vanished or transformed into ecological deserts.”
Citing that migratory birds operate on extremely tight energy budgets, he says that arriving at a depleted site means they cannot accumulate the fat reserves needed for the next leg of their journey.
“This leads to increased mortality en route, reduced breeding success upon reaching their destinations due to poor physical condition, and a long-term decline in population viability,” the zoology professor says.
Suggesting a flyway-scale approach, Zulfiquar emphasizes the need for rigorous protection, restoration of remaining key wetlands through strengthened legal frameworks, designation of new protected areas, and sustainable water management policies that ensure ecological flows to downstream ecosystems.
“International cooperation along the flyway is also essential, as the birds are a shared responsibility,” he adds.
Conservation must go beyond borders
As the CAF coordinator at BirdLife International, Anand Chaudhary is aware of the discussed problems and consequences.
However, he indicates a silver lining. He says, “Many habitats, such as patches of woodlands, community forests and wetlands, are being protected either by the governments or local communities.”
He cites that Bangladesh and India have signed the UN Convention on Migratory Species, adding another layer of commitment from the national level for supporting species and site conservation.
“What we may see in South Asian countries is increased utilization of safe havens and concentration of species in these areas as inhospitable or degraded sites are abandoned,” Anand says.
Anand praises the growing role of civil society organizations, including Bombay Natural History Society (BNHS) in India, SCOPE Foundation in Bangladesh, Bird Conservation Nepal (BCN) in Nepal, Royal Society for Protection of Nature (RSPN) in Bhutan and Field Ornithology Group of Sri Lanka (FOGSL) in Sri Lanka, working on the ground to protect migratory bird habitats.
“We are optimistic that, over time, we can mobilize communities, conservation organizations, private sector, and governments to enhance the conservation of these safe havens for migratory birds,” Anand says.
Banner image: Fishermen and birds coexist in harmony on almost all mudflats of coastal Bangladesh. Image by Sayam U. Chowdhury.
Bird diversity drops in human-dominated habitats, Nepal study suggests
Citations:
Mundkur, T., Ananzeh, A., Chaudhary, A., Evans, M., Jia, Y., Koshkina, A., Kumar, R., Nergui, J., Niven, R., Rao, M., Scott, T., & Al Taq, M. (2023). Central Asian Flyway: Situation analysis—The status of migratory birds and their habitats and recommendations for their conservation. BirdLife International. doi:10.13140/RG.2.2.32281.80480
Bird Conservation Nepal [BCN], Department of National Parks and Wildlife Conservation [DNPWC], & Department of Forests and Soil Conservation [DOFSC]. (2024). Important bird and biodiversity areas in Nepal: Key sites for conservation. Bird Conservation Nepal. Retrieved from https://birdlifenepal.org/public/uploads/files/IBA_Book-2024_Final_Copy-compressed_compressed.pdf
Pema Dendup, Wangdi, L., Jamtsho, Y., Kuenzang, P., Gyeltshen, D., Tashi, T., Rigzin, U., Jamtsho, Y., Dorji, R., Dorji, R., Jamtsho, Y., Lham, C., & Tshering, B. (2021). Bird diversity and conservation threats in Jigme Dorji National Park, Bhutan. Global Ecology and Conservation, 30, e01771. doi:10.1016/j.gecco.2021.e01771
Kumari, T., Phogat, D., Kumar, P., & Shukla, V. (2025). Migratory birds’ diversity at different national parks in India. Asian Journal of Conservation Biology, 13, 183–194. doi:10.53562/ajcb.85039
Steibl, S., Zareer, I. H., Khaleel, H., Fox, M., Nidham, H., & Russell, J. C. (2025). Status of common breeding and migratory birds in the Maldives (OCPP project report). Maldives Environmental Protection Agency. Retrieved from https://www.researchgate.net/publication/390240622_Status_of_common_breeding_and_migratory_birds_in_the_Maldives
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