IW9 Inland water breeding birds

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Development

Inland water breeding bird indicator sums up the development of 24 species of both oligotrophic and eutrophic habitats based on data from the whole country. The indicator has been divided into two species groups: Black-throated Loon, grebes, Whooper Swan, ducks and Eurasian Coot (A, Waterfowl) and Gulls and Common Tern (B). The population development of certain typical species of eutrophic habitats (*) has been interpreted to represent the trends of eutrophic inland waters only. The observations of other species have been divided into oligotrophic and eutrophic groups based on the characteristics of the observation site.

In oligotrophic inland waters the waterfowl indicator (A) has fluctuated quite markedly yet over the whole period populations have grown by approximately 30%. At the same time, gulls and Common Tern (B) have nearly quadrupled in population.

In eutrophic inland waters waterfowl populations have declined by approximately 55% since the beginning of 1990s. Gulls and Common Tern have declined by 30%. The indicator for all inland water habitats develops almost similarly to the one of eutrophic conditions since populations sizes are much greater in those circumstances.

Inland water birds

Distributions of most indicator species represent almost the whole country. Southern species include Red-necked Grebe, Horned Grebe, Garganey, Northern Shoveler, Common Pochard, Eurasian Coot and Lesser Black-backed Gull. Distributions of Northern Pintail and Smew focus on the North.

Rising of inland water birds population in 1980s and 1990s resulted from increased richness of Mallard, Eurasian Wigeon, Common Goldeneye, mergansers, Eurasian Coot and Red-necked Grebe. Since then populations have been mostly descending. One exception is Mallard, which stock has grown by approximately 40 % over the whole period. Populations of Whooper Swan, Black-throated Loon, Red-necked Grebe and Smew have also increased.

Population developments of Tufted Duck and Common Pochard seem to be outstandingly alarming: over the whole period they have both declined by circa 80 % both in eutrophic and in oligotrophic inland waters. Population of Horned Grebe has declined by circa 75 %. Stocks of Northern Shoveler and Garganey have declined to less than a half of the previous. Northern Pintail has declined by approximately 40 % over the whole period.

Population of Black-headed Gull has declined quite smoothly over the whole period, with the exeption of growth in the couple of recent year, and is now less than a half of the previous stock. Lesser Black-backed Gull declined strongly (by over 50 %) in the late 1980s and yet has not recovered. Data of other gulls and Common Tern does not indicate major changes.

Causes behind differences in population development between eutrophic and oligotrophic waters have not been studied. Because both long and short distance migrators have declined, the most important reasons are probably linked in nesting areas. It is possible, that eutrophic inland water habitats have degenerated relative to water birds. One reason might be diminution of Black-headed Gull. Aggressive gulls defend their nests against predators, thus water birds can manage better when living in gull community. Increasing of mammal predators can raise predation pressure more in eutrophic waters. In addition, more eutrophication of eutrophic water body can lead to vegetal invasion of water and to degradation of water quality.