How Monsoon Floods Turn Bangladesh’s Sundarbans and Haors Into a Bird Superhighway

September 11, 2026
2 mins read
Monsoon floods

When the monsoon rains arrive in Bangladesh, they do more than fill rivers and test flood defences. Across the Sundarbans and the wetlands of the northeast, the monsoon floods build one of the richest bird habitats. The East Asian-Australasian Flyway is one of the busiest migratory bird routes on the planet.

What Happens to the Sundarbans During Monsoon

In September, heavy rainfall pushes water levels up across the Sundarbans delta. Channels widen, new waterways form, and large sections of the mangrove forest turn into wetland. This flooded landscape creates shallow, insect-rich margins. These haors are ideal feeding and resting grounds for birds moving through the region.

How the Haors Become an Inland Sea

Further north, in the low-lying haor basins of greater Sylhet, the effect is even more dramatic. fill with water until dozens of small lakes, beels, merge into what looks like a single inland sea stretching across the horizon. As the dry season sets in and the water slowly recedes, it leaves behind a patchwork of lakes, marshes, and grassland.

Why This Matters for Migratory Birds

The East Asian-Australasian Flyway sees many birds breeding in the areas of Siberia, Central Asia, and the Himalayas. Bangladesh is located on the Flyway, where coastal and terrestrial wetlands serve as crucial stations. Tired birds can feed and take a break before they move on.

One of the significant sites, Hakaluki Haor, is known for having a large number of migratory birds. They visit to feed once the monsoon floods recede. Another example is Sonadia Island, located next to the Bay of Bengal. This one is known to be crucial for many types of birds including the Great Knot, thus forming a chain of important stations across the Flyway.

Which Species Benefit Most

Ducks, geese, sandpipers, and plovers make heavy use of the shallow margins that monsoon flooding creates. Larger wading birds such as the Asian openbill, painted stork, spot-billed pelican, and river tern depend on exposed sandbars. Flooded forest patches to feed and rest during their journey. Even resident species feel the effect of the season. The House Swift, for example, becomes noticeably more active as insect numbers surge across the Sundarbans.

A Changing Climate Adds Pressure

Nevertheless, not all aspects associated with the changing monsoon season are beneficial to birds. The rainfall can deteriorate the nesting habitats of blue-tailed bee-eaters. On top of that, changing water levels can negatively affect the shallow feeding areas utilised by many water birds. Scientists monitoring these events have put pressure on the species that struggle in the conditions of limited wetlands.

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It’s Important to Preserve Such Wetlands Not Only for Birds

The Sundarbans and haor basin are valuable not only from the wildlife perspective. Coastal wetlands have proved to be unique flood and storm protection areas per hectare. This makes their protection beneficial for humans just as much as for birds living in those areas. According to the environmental advocate, these migratory birds rely on interconnected locations. The preservation of the wetlands in Bangladesh is only one part of the larger process.

FAQ

When is the best time to see migratory birds in Bangladesh? 

Winter, roughly November through February, is peak season. Once monsoon floodwaters have receded and left behind rich feeding grounds.

Which flyway passes through Bangladesh? 

The East Asian-Australasian Flyway, one of the world’s major migratory bird routes connecting Siberia and Central Asia to Southeast Asia.

Which Bangladeshi sites are most important for migratory birds? 

The Sundarbans, Hakaluki Haor in the northeast, and Sonadia Island on the Bay of Bengal coast are among the most significant stopover sites.

Payel

Payel

Payel is a journalist and writer with a deep commitment to storytelling. Passionate about nature, the environment, and the human stories intertwined with them, she aims to highlight issues that shape our world and inspire meaningful change.

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