A three-day bird expedition in the Sundarbans at the start of this year has recorded 153 species and 31,927 birds.

The sightings also included non-migratory birds. Among the total number of species recorded, 13 are threatened.

The mangrove delta is a vital pit stop for migratory birds. Two of the eight well-established migratory routes — flyways — on the planet overlap in the Sundarbans, said veteran birders and foresters. The great knot, red knot, godwit, sanderling and common crane are some of the migratory birds that use the delta as a stop.

The third edition of the Sundarbans Bird Festival was held from January 22 to 26. From January 23 to 26, six teams of photographers set out on boats to trace the birds along different routes of the delta — islands interspersed in a maze of rivers and creeks. Each of the six teams had a forest staff and a "resource person".

They covered the National Park East and West, Basirhat, Sajnkehali wildlife Sanctuary in the Sundarban Tiger Reserve, and Matla and Kalas ranges in the South 24-Parganas forest division.

Forest minister Birbaha Hansda revealed a portion of the report's findings at Sajnekhali on Thursday.

Most species (108) were recorded from the Matla range, followed by Kalas (95) and National Park West (81). Some of the species overlap different ranges.

The report listed 48 species of mudflat birds; 11 raptors; 87 forest birds, and seven kingfishers.

The 13 threatened species recorded included the Eurasian curlew, grey plover, great knot, common redshank and brown-headed gull.

Every year, hundreds of thousands of migratory birds embark on a transcontinental journey. Typically, the journey links northern breeding grounds in Arctic and temperate regions — where winter is extremely harsh — with warmer non-breeding (wintering) sites in temperate and tropical areas.

"The number of birds sighted in non-protected areas along the Matla route is much higher than the number of birds sighted in protected areas. This shows that for certain species, the habitats found in non-protected areas are more suitable. They congregate in those locations in greater numbers. There needs to be a considerable degree of protection and habitat conservation in these hotspots," said a forest official.

The previous edition of the festival had recorded 145 species, and 8,776 birds were sighted. In 2024, the teams were out on boats for two days.