According to their geographical origin, the delta birds contain the following types: arctic species (27); Siberian (32); European (108); Mediterranean (29); Mongolian (33); Chinese (2). The transpalearctic type contains 43 species. For Romania's latitude – delta included – the north-originating species (Arctic and Siberian) appear as winter-and passage birds, while the south-originating species (European, Mediterranean and Mongolian) are met with as sedentary and summer species.

The Common Moorhen (Gallinula chloropus) is a bird in the Rallidae family with an almost worldwide distribution.
It lives around well-vegetated marshes, ponds, canals and other wetlands. The species is not found in the polar regions, or many tropical rainforests. But elsewhere the Common Moorhen is likely the most commonly seen rail species to most people, excepting the Eurasian Coot or American Coot in some regions.
This is a common breeding bird in marsh environments and well-vegetated lakes. Populations in areas where the waters freeze, such as southern Canada, the northern USA and eastern Europe, will migrate to more temperate climes. This species will consume a wide variety of vegetable material and small aquatic creatures. They forage beside or in the water, sometimes upending in the water to feed. It is often secretive, but can become tame in some areas. Despite loss of habitat in parts of its range, the Common Moorhen remains plentiful and widespread. They fight over territories and also hop around Lily pads.