Migratory birds are of great ecological and economic value as they are an integral part of the global biological diversity. Nearly half the world's 10,000 bird species depend on forests, wetlands and grasslands - they are inhabitants of virtually all ecosystems of the world.

They can be labeled some of the best indicators for the status and trends of wider biodiversity. Bird species are an excellent example for the enormous diversity created by Mother Nature on earth.

Because they travel from ecosystem to ecosystem and because of their ability to fly, birds occupy a wide range of ecological positions, which normally would be out of reach for mammals. These capabilities of birds, all possible because of flight, contribute to the relatively high number of bird species. While some are generalists, others are highly specialized in their habitat or food requirements.

Each year more than 800 species of migratory birds confront stiff winds, harsh weather and numerous predators to fly thousands of miles to a more suitable climate. In order to survive these long and exhausting journeys migratory birds depend on different stopover habitats where they can rest safely and find enough food Strategically located patches of woods, wetlands, mudflats and beaches with adequate food and shelter ensure the survival of the species.

Through their annual cycle, migratory birds cross many countries and continents, some of them from the tundra to the tropics, linking different ecosystems. Many sites - identified as the key sites for birds, so called Important Bird Areas (IBA) - host numerous other threatened species of plants and animals. Therefore areas important for birds represent hot spots for other biodiversity as well. By conserving them and their environment we ensure the conservation of biodiversity on a wider scale. Key biodiversity areas form the anchors of an efficient ecological network on a global scale. Like the IBAs, they can be identified based on the species they hold.

Generally we have more data on the status and distribution of bird species than on other animals, which often is poor or patchy. This makes it particularly hard to identify the critical sites for these species. More than any other organisms, birds represent the concept of global biodiversity by spinning a web of interconnected and overlapping flyways that enfold the planet, illustrating its role as a global habitat.

Bangladesh is occupying a unique geographical location in the South Asia. Virtually, the delta is the only drainage outlet for a vast complex river basin made up of the Ganges, Brahmaputra and Meghna River and their network of tributaries. There are three broad physiographic regions in the country. The floodplains occupy about 80 percent; terrace about 8 percent and hills about 12 percent of the land area. So it is evident that with 80 percent floodplain, Bangladesh is a land of water and wetlands. According to the definition enunciated in the Ramsar Convention, more than two-thirds of the country's landmass may be classified as wetlands. It is a country dominated by wetland encompassing a wide variety of dynamic ecosystems such as that is estuaries, mangroves namely the Sundarbans, freshwater marshes such as haor, swamps and rivers. The wetlands are the important habitat of migratory waterbird population. There are about 628 bird species in Bangladesh, out of which 244 are Migratory. The wetlands are the abode of about 70 species of resident waterbirds including ducks, grebe, cormorants, bitterns, herons, egrets, storks, rails, jacanas, finfoot, waders, gulls, turns, skimmers etc. and many other water dependant birds. As mentioned in the IUCN Red Book, about 100 species of migratory birds regularly or occasionally visit the country.

Birds are obviously important members of many ecosystems. They are integral parts of food chains and food webs. In a woodland ecosystem for example, some birds get their food mainly from plants. Others chiefly eat small animals, such as insects or earthworms. Birds and bird eggs, in turn, serve as food for such animals as foxes, raccoons, and snakes. The feeding relationships among all the animals in an ecosystem help prevent any one species from becoming too numerous. Birds play a vital role in keeping this balance of nature. In addition to being important parts of food webs, birds play other roles within ecosystems.

1. Birds eat insects. They are a natural way to control pests in gardens, on farms, and other places. A group of birds gliding through the air can easily eat hundreds of insects each day. Insect eating birds include warblers, bluebirds and woodpeckers.

2. Nectar-feeding birds are important pollinators, meaning they move the pollen from flower to flower to help fertilize the sex cells and create new plants. Hummingbirds, sunbirds, and the honey-eaters are common pollinators.

3. Many fruit-eating birds help disperse seeds. After eating fruit, they carry the seeds in their intestines and deposit them in new places. Fruit-eating birds include mockingbirds, orioles, finches and robins.

They also the indicator of an ecosystem.

Such as Pallas fish eagle if it decreased from wet land then it's indicate the protein sources of wetland fish population is drop in and tall trees are also decreasing.

Ferruginous Pochard depends on Aquatic plants and shrubs of wetland, if their population is decreasing then Aquatic plants and shrubs are remitting, wet land will be unsuitable for fishes alongside with birds.

Some say "Migratory Birds causes bird flu and other infectious diseases".

When individuals periodically leave contaminated habitats through migration, they can reduce the incidence of disease. During migration periods, members of a species are more separated from each other; at the same time, infected individuals rarely survive are long-distance movement. Because birds are so common in most habitats, we often overlook their ecological significance. However, their ecological roles are incredibly important and humans can benefit monetarily through the many actions of birds. The examples described above are just a few of the many ways that birds provide ecosystem services. Quantifying the monetary benefit from birds around the world is nearly impossible.

We have taken an ecological approach by focusing on ways that birds provide services to humans through their interactions with the environment. However, it should also be noted that the direct take of birds and their products also provides economic benefit in many cases. The value we gain from birds warrants a serious investigation into causes of declines and provides additional rationale for the continued study and conservation of these animals.

Dr. Ahmad Kamruzzaman Majumder, Chairman, Department of Environmental Science, Stamford University Bangladesh and Naim Rashid, Research Associate