With the advent of winter however some migratory birds have converged on the city's remaining wetlands like Mirpur Ceramic lake, Dhaka Zoo, Jahangir Nagar University area, Botanical garden, Ramna park, Dhaka University area and on the banks of Buriganga and Dhaleshwari river.

"Migratory birds are decreasing day by day both in terms of quantity and species," said Sajahan Sorder, president of Bangladesh Bird Watchers' Society, secretary-general of Nature Conservation Committee (NCC) and also an individual bird-watcher for the last 30 years.

Migratory birds arrive from the frozen Himalayas, Central Asia, North Asia, East Europe and the Far East between mid-September and early November. They fly away between early March and late April.

The NCC had initially recorded 116 species of migratory birds, based on annual censuses starting from January 2002. But the current census on 48 wetlands has found only 40 species of such birds.

From the year 1991 to 1994 NCC recorded around 5,000 migratory birds in Dhaka Zoo area. But in the year 2005 the number drastically dropped to 706.

The habitat of Dhaka Zoo is more congenial than Mirpur Ceramic Lake. But number of migratory birds of Dhaka Zoo and Jahangir Nagar University area is decreasing for several reasons, said Sajahan.

"People's attitude toward the migratory birds is not pleasant. Human trap and crowding are main reasons behind the reduction of migratory birds in Dhaka Zoo," said Sajahan.

The zoo authority admitted a drop in the number of migratory birds in zoo in the last few years. They said urbanisation near the zoo area has driven the birds away. Fearing that the migratory birds could spread bird flu, a section of zoo officials also prevented the birds from settling on the lake.

"To save zoo inmates from flu, we discourage migratory birds to visit this place and clean hyacinth from the lake, because it attracts the birds," said Kazi Fazlul Haque, curator of Dhaka Zoo.

Migratory birds are of two types; aquatic and non-aquatic. The aquatic birds usually come from the Himalayas, Central Asia, North Asia, East Europe and the Far East. Different types of ducks including marsh duck and diving duck are seen in the city for the last 15 years.

Among the non aquatic (bush, leaf and forest birds) birds red breasted fly catcher, grey headed fly catcher, dusky warbler, babbler, flower pecker, shrike are seen in the city.

According to bird specialists, botanical garden is the best place for non-aquatic warbler and babbler.

Other than these a large number of resident birds live in well-wooded area. Well-wooded jungle birds from other districts of Bangladesh migrate to several spots in the city.

Resident birds migrate to several places at daytime to take shelter and for security as during this season they do not feel safe in their nests for human trap. As these birds are weed eaters, they search for food in nearby areas at night, said the bird experts.