Ferrantia, Volume 86: Beobachtungen zur Entwicklung der Wasservogelwelt nach der Renaturierung der Sauer unterhalb von Steinheim [Observations on the Development of Waterfowl after the Ecological Restoration of the Sauer below Steinheim]

About this book

Language: German with trilingual summary in English, German, French

To protect adjoining villages from flooding, the bed of the river Sauer below Steinheim, a town in eastern Luxembourg, was restored by dredging two silted-up oxbow lakes of the river. This created two elongated islands separating the main stream from both sideways. After completion of work in the year 2010, regular counts and observations of waterbirds took place in the area for the next 10 years. The data collected are analysed here.

The development of monthly maximum numbers of waterbirds counted in a year displays a general pattern with decreasing numbers towards summer and remaining low until autumn when they start to increase. Winter numbers are fluctuating. Some years may escape to this global scheme. A comparison of the different years shows a rather steady increase of average waterbird numbers until 2014, the population remains high for the next four years and then tends to decrease. Species strongly influencing total population numbers at least over some years were especially Egyptian Goose Alopochen aegyptiaca, Mallard Anas platyrhynchos, Mute Swan Cygnus olor, Little Grebe Tachybaptus ruficollis and Eurasian Coot Fulica atra. A total of 56 different waterbird species occurred in the area below Steinheim. Mute Swan, Canada Goose Branta canadensis, Egyptian Goose, Mallard, Little Grebe, Great Crested Grebe Podiceps cristatus, Common Moorhen Gallinula chloropus, Eurasian Coot and Eurasian Kingfisher Alcedo atthis were regularly breeding. Great Cormorant Phalacrocorax carbo, Grey Heron Ardea cinerea and Great Egret Ardea alba were regular guest birds. In Winter, Common Merganser Mergus merganser occurred in all years and during migration and in summer Common Sandpiper Actitis hypoleucos, Green Sandpiper Tringa ochropus and Little Ringed Plover Charadrius dubius often visited the river section investigated. In some years, broods of the latter were suspected. The majority of the species however concerned irregular guests and exceptional occurrences.

Many breeding species increased their population over the first years, but this was followed by quick decreases in species like Little Grebe, Common Moorhen and Eurasian Coot, and to a lesser degree by Mute Swan and Egyptian Goose. The high breeding success of the local pair of Great Crested Grebes possibly contributed to settlement attempts by further conspecifics beginning in the year 2016, however these go hand in hand with massive territorial disputes between the pairs. Reasons for declining breeding populations can be found in a degradation of the habitat and increasing anthropogenic disturbances. They are probably also the cause for lower numbers of several guest birds.

Different indices were calculated to assess the development of species diversity and species richness of the area investigated. They failed to display a uniform picture, especially with respect to the last five years. It was not possible to compare the situations before and after restoration as no data of waterbird occurrences were collected prior to the remodelling. Nevertheless, all results tend to depict an increase in ornithological biodiversity over the first years after restoration followed by a flattening or even a slightly negative course of the curve over the last years.

Comparing the list of waterbirds registered with the list of potentially possible species according to status, it appeared that all regular and all rare breeding birds of Luxembourg did occur below Steinheim. 6 of 8 regular and one of 2 rare winter guests were also observed and 7 of 8 regular and 14 of 18 rare birds of passage stopped there, too. In total, 45 of 53 possible species in these categories or 85% were observed. With exceptional sightings, very rare vagrants and escaped species, the balance is worse; only 11 of 71 potential species visited the area investigated.

The high percentage registered with species that one could expect because they stay more or less regularly in Luxembourg underlines the national signification of the restored section of the river Sauer. It is discussed, to what extent better protection and more efficient planning of care measures are required, to preserve and consolidate the importance of the area for waterbirds.

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