Chilika is one of the hotspots of biodivesity in India.  It's part freshwater and part saltwater character, very high productivity and the presence of a variety of habitats in and .
 

around the lake allow the proliferation of an amazing number of species. Chilika is one of the terminuses on the migratory flyways and some of the largest congregations of aquatic birds in India can be seen here, particularly in winter.
 

Chilika is famous for the huge congregations of migratory waterfowl flocks there every winter.  The lagoon is well-known to support the largest concentration of migratory waterfowl in India - especially in 1989-90, there were 2 million birds visited Chilika (Bandyopadhyay and Gopal 1991).  Due to the immensity of the lake birds are either in passage or wintering in the area. The constant shifting of feeding grounds along the lagoon makes it very hard to gauge the species composition and relative abundance of different species (Mohapatra and Hussain 1988). Some of the information is taken from (Ram, R. et al. 1994).  The lagoon hosts over 160 species of birds in the peak migratory season, and at least 97 of these are intercontinental migrants (Hussain et al. 1984, Dev 1988; Prakriti Samsad 1984).  "Birds from as far as the Caspian Sea, Lake Baikal, Aral Sea and other remote parts of Russia, Kirghiz steppes of Mongolia, Central and southeast Asia, Ladakh and Himalayas come here" (Bandhyopadhyay and Gopal 1991).  These birds travel great distances as shown in the table (Mohapatra and Hussain 1988).  It must be stressed, however, that the migratory birds probably follow much longer routes than the straight lines indicated o the map, possibly up to 12,000 km, to reach Chilika.  Of the species recorded, 32 percent are aquatic birds, 22 per cent are waders and 46 per cent are terestrial, including 14 types of birds of prey.
 

Huge flocks of birds scattered throughout the lake of major concentration in terms of species abundance is on Nalbana island, declared a bird sanctuary since 1973.  Nalbana island, declared a bird sanctuary since 1973.  Nalbana in Oriya means a weed covered island (Mohapatra and Hussain 1988).  The 32 sq. km island gets completely submerged during the monsoons and almost no birds can be seen there.  As the monsoon waters recede, the island gradually emerges.  At the beginning of the migratory season, long-legged waders and dabbling species are predominant.  As the island gradually dries up, small wading species congregate on the islands.  During December-January a large number of ducks, fish-eating birds and smaller waders flock to feed or roost.  By summer almost all the birds leave and only a few songbirds and resident shorebirds remain.  Other areas where high concentrations of birds are found nclude Gerasara, Parikud island, and the western shores of the Northern sector (Chatrath 1992).
 

Bombay Natural History Society carried out series of bird ringing and trapping operations in sixties and early eighties to assess winter migration strategies and routes (Mohapatra and Hussain 1988).  Ornithologists of the Zoological Survey of India completed a study of the birds at Chilika (1984-90).  A waterfowl census carried out in 1991 recorded huge numbers of Shovellers (99,670), Pintails (50,690), Coots (46,280), Gadwalls (30,890) and Great Crested Grebes (15,692).  The maximum number of birds recorded in various counts is given (Anonymous 1992).

One of the most fascinating sights in Chilika is that of large flocks of flamingos feeding in the shallow waters of the lagoon.  Flamingos come to Chilika from Iran and the Rann of Kutch in Gujarat.  Recently, they have started staying for longer periods in larger numbers, and some remain the year round (Chatrath 1992).  Other Long-legged waders seen around Nalbana are Lesser Flamingos, Grey and Purple Herons, Egrets, Spoonbills, Storks and White Ibis. Compact gregarious flocks of Brahminy Ducks, as well as Shovellers, Pintails, Gadwall, Teals, Pochards, Geese and Coots, can be seen all around Nalbana island.

A few birds such as the Short-legged Shorebirds restrict themselves to a narrow band along the shifting shores of the lake and islands.  These include several Plovers, the Collard Pratincole, Ruff, Dunlins, Snipes and Some Sandpipers.  Larks, Wagtails and Lapwings are also found on the mudflats.  Venturing into deeper water are the Longer-legged Avocets, Stilts and Godwits.  The vegetated areas of the lake support moorhens, Coots and Jacanas.  Pond Herons and Night Herons can be seen along the shores as also Kingfishers and the Roller.  The Little Cormorant is seen on perches around the lake, and is increasingly using the bunds being built by fishermen.

There are many raptors found around the lagoon especially the Pariah Kite is the most common raptor and Brahminy Kites are also seen frequently.  Marsh Harriers and Palla's Fishing Eagles are seen around the flocks of ducks and coots, specially at Nalbana.  Ospreys are infrequent at Chilika, but the endangered White-bellied Sea Eagle is seen fairly often.  Winter visitors include the Kestrel and the globally threatened Peregrine Falcon.

A few important birds recorded at Chilika are the Spoonbilled Sandpiper, the Asiatic Dowitcher (also called the Snipebellied Godwit) and the Goliath Heron.  The Spoonbilled Sandpiper (Eurorhynchus pygaemus) is a very rare winter migrant.  It has been recorded only four times in India over the last fity years.  One was seen at Chilika in 1981.  This tiny wader weighs only 20-22 gm (as little as a Sparrow) and migrates all the way from Siberia to winter in India.  A small number of Asiatic Dowitchers (Limnodrilus semipalmatus) regularly visit Chilika.  This bird is a rare vagrant in India (Mohapatra and Hussain 1988).  As many as 41 Dowitchers have been seen at Chilika at one time.  The Goliath Heron (Ardea goliath) is another rare species spotted in Chilika.  As large as a Sarus Crane, this bird has been recorded only a few times in India.

Ornithologists have reported that at least five species have been spotted breeding on Nalbana island at the end of March, when the island is fairly dry.  These are the Little Tern, Gullbilled Tern, Blackwinged Stilt, Eastern Skylark and Collard Pratincole (Hussain et al. 1984).  Several other birds, including several terrestrial birds, probably breed around the area.

During a recent survey by BNHS (2002) the nesting colonies of Gull-billed and River terns were observed on the Nalabana Island which appear to be the largest known breeding colonies for these two species.  Moreover, the breeding records of Gull-billed Tern in Chilika are a southern breeding range extension for the species, as its known breeding sites from the Indian Subcontinent are Pakistan on the west coast and Sunderbans (West Bengal) on the east coast. The Indian River Tern which has restricted distribution range (India, Pakistan, Bangladesh, Nepal, South West China, Myanmar, and Malayan Peninsula) is one of the least studied species. Though River Tern breeds sporadically throughout India (scarce in southern peninsular India), smaller number of nests were noticed in each colony.  The 540 nest record of Nalabana is the largest nesting colony in the south-east Asia for this species. In addition to this, 205 number of birds were check-listed by BNHS during the course of their study from December, 2001 to May, 2002.