Gravel-nesting birds under threat
Little Ringed Plover and Common Sandpiper, both typical species of floodplains, are not faring well in Switzerland. Human interventions have tamed rivers and decreased their value as a habitat for these two wader species. Restorations alone do not guarantee success, as flooding and disturbance from recreational activities often cause breeding failure.
Little Ringed Plover and Common Sandpiper nest on the large gravel banks of our rivers. The Common Sandpiper relies on extensive, undisturbed and semi-natural floodplains. On slow-flowing stretches of river, fine sediment such as gravel, sand or silt is deposited; the pioneer vegetation that grows there provides cover for the Common Sandpiper to hide its nest. Because the state of rivers today mostly fails to meet the species’ needs, the population can barely survive. All breeding sites on the Central Plateau were abandoned long ago.
The Little Ringed Plover, on the other hand, is a pioneer species that can colonise temporary sites with gravel and little or no vegetation; it can also revert to habitats connected with human activity (e.g. gravel pits, military training grounds, building sites), though it originally relied on natural, free-flowing rivers as well. Human intervention has caused the majority of suitable gravel areas to disappear. As a result, only about half the Swiss population of Little Ringed Plovers now breeds on rivers. In Bavaria, this figure has dropped to less than 10 %; the rest of the population breeds in alternative habitats. In part because of their small numbers, both species are classified as «Endangered» on the Swiss Red List.
Massive loss of habitat
In Switzerland, typical floodplain species face difficult conditions on rivers and at river mouths on lakes. The floodplains are mostly small due to the topography of the region, and high flow velocity causes fine sediment to be swept along rather than deposited. Heavy rainfall typical for June storms in the mountains is often exacerbated by the snow melt. This happens at a time that is crucial for the breeding success of gravel-nesting birds.
Increasing human interventions since the first river regulations in the 18th century add to the difficulties of the natural landscape: river canalisation, construction of power stations and infrastructure, weirs, gravel extraction, and altered sediment deposition. Interventions on the riverbed are aggravated by the effects of hydropeaking. These sudden, massive changes in the water level caused by hydropower plants pose an additional threat to breeding waders. Other dangers include flushing to remove trapped sediment from the channel and predation pressure (e.g. by crows and foxes). Finally, gravel-nesting birds face frequent disturbance from human recreation.
The Rhine – a haven for the Little Ringed Plover?
The situation on a stretch of the Rhine between Chur GR and Lake Constance exemplifies the problem. Once notorious for frequent flooding, the Rhine was straightened and confined in several stages from 1861. Today, the entire length of the river is canalised. Meanwhile, a number of peninsulas have formed between Sargans SG and Rüthi SG. While the Common Sandpiper may at best make an exceptional breeding attempt on these gravel bars that lack a protective cover of vegetation, the areas are attractive for the Little Ringed Plover. When water levels are favourable, about 30 pairs gather here in April. But a canalised river has downsides for the Little Ringed Plover as well. Because the riverbed has been narrowed, the water rises more rapidly, and at the onset of snow melt, the first gravel banks are soon flooded. Also, islands that would provide better protection from human disturbance and land predators are unable to form. The only advantage for the Little Ringed Plover is that frequent high water and torrential floods keep the gravel banks largely free of vegetation. Population surveys conducted since 1989 by H. Aemisegger suggest that in many years, the birds cannot produce enough offspring to compensate for natural losses.
Restoration can have a positive impact
Since the start of the millennium, many stretches of river have been restored in Switzerland, mainly for the purpose of flood protection. In the coming decades, rivers are to be given back at least some of the space they have been deprived of. This is required by the Federal Act on the Protection of Waters, revised in 2011. Gravel-nesting birds have already been able to benefit from some such restoration projects: The Common Sandpiper quickly reappeared on the revitalised sections of the Inn in Upper Engadine GR. Other revitalised stretches of river where the Common Sandpiper has bred in at least some years include the Moesa GR, the Rhine near Felsberg GR, the Kander BE and the Rhone VS (Pfynwald). In the Reuss delta UR and Kander delta BE, the species has also benefited from restorations. However, the efforts made so far have been insufficient to encourage the return of the species to the Central Plateau. Factors that have limited the success of restoration projects include the failure to provide large-enough surface areas, and poor management of visitor flow. In places where recolonisation by the Little Ringed Plover has been successful, for example on the Thur River, continuing effort is required to protect breeding sites from human disturbance. Also, some breeding islands became unsuitable after only a few years because vegetation grew too rapidly due to poor maintenance and reduced river dynamics. Extra effort must be put into future restoration projects so that gravel-nesting birds and other typical floodplain species can truly benefit and raise their young without disturbance.
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