Over 300 species of bird have been recorded, of which over 176 species breed, the most important being:

• Cormorant Phalacrocorax carbo sinensis (3,000 pairs)
• Pygmy cormorant P. pygmeus (K) (2,500 pairs comprising 61% of the world’s population)
• White pelican Pelecanus onocrotalus (2,500 pairs comprising 50% of the Palaearctic breeding population)
• Dalmatian pelican P. crispus (E) (estimated at 150 pairs, perhaps now only 25-40 pairs, on the floating islands on lake Hrecisca, which represents 5% of the world population)
• Night heron Nycticorax nycticorax (2,100 pairs), squacco heron Ardeola ralloides (2,150 pairs)
• Great white heron Egretta alba (700 pairs)
• Little egret E. garzetta (1,400 pairs)
• Purple heron Ardea purpurea (1,250 pairs)
• Glossy ibis Plegadis falcinellus (1,500 pairs)
• White stork Ciconia ciconia (many)
• Mute swan Cygnus olor (500 pairs)
• White-tailed eagle Haliaeetus albicilla (V) (8 pairs)
• Marsh harrier Circus aeruginous (300+ pairs)
• Osprey Pandion haliaetus (3 pairs)
• Saker falcon Falco cherrug (1-2 pairs)
• Red-footed falcon F. vespertinus (150 pairs)
• Sandwich tern Sterna sandvicensis (1,700 pairs)
• Common tern S. hirundo (20,000+ pairs)
• whiskered tern Chlidonias hybridus (20,000+) and black tern C. niger (10,000-20,000 pairs)
• White-headed duck Oxyura leucocephala possibly still breeds
• Slender-billed curlew Numenius tenuirostris (K) has occurred on passage (28 in 1971 and one or two in 1989)
• The Delta holds huge numbers of Anatidae in the winter with counts of 500,000 white-fronted goose Anser albifrons (but only 64,000-77,500 in 1982), up to 500 lesser white-fronted goose A. erythropus, 45,000 red-breasted goose Branta ruficollis (a globally threatened species with almost 95% of the world wintering population present here), 150,000 teal Anas crecca, 200,000 mallard A. platyrhynchos, 14,000 pintail A. acuta, 40,000 shovelor A. clypeata, 32,400 red-crested pochard Netta rufina, 970,000 pochard A. ferina, 13,000 ferruginous duck A. nyroca, and 1,500 red-breasted merganser Mergus albellus. In winter there is a concentration of some 30-40 Haliaeetus albicilla.

For birdwatching you have to noticed that:

The White Pelican (pelecanus onocrotalus)
In March, swaths of white pelicans leave the Nile Delta and the Red Sea to come nest in the Danube Delta. The Delta is home to Europe’s largest breeding population (some 3,500 pairs).
Best seen: March to October

Dalmatian Pelican (pelecanus crispus)
After decades of decline, this species’ numbers have slowly begun to increase in the Delta. Currently, some 150 pairs have been spotted in several small colonies.
Best seen: April to October; some pairs may stay over the winter.

Small Egret (egretta garzetta)
A migratory species protected by law, the small egret lives in marshy areas and nests in small willows.
Best seen: April to October; some pairs may stay over the winter.

Pygmy Cormorant (phalacrocorax pygmeus)
Best seen: April to October; some pairs may stay over the winter

Ferruginous Duck (aythya nyroca)
The Danube Delta may be the last place in Europe to see this declining species. In August and September, large numbers often gather at Somova Lake, just west of Tulcea.
Best seen: March to October

Red-breasted Goose (branta ruficollis)
In winter, thousands of this species – almost half of the entire world population – reside on the Razim-Sinoe lagoon and coastal plain to the south of the Delta.
Best seen: Late October to March

Glossy Ibis (plegadis falcinellus)
More than 30% of the European population nests in the reed beds of the delta.
Best seen: April to September