© Marcel Burkhardt
In this recovery programme, the causes of the drastic population decline of the Black-headed Gull are investigated and appropriate conservation measures worked out.
During the last 20 years, Black-headed Gull populations have declined throughout Europe in the inland and partly also along marine coasts. In Switzerland, too, the breeding population has decreased by 74 % during this period. The Swiss population trend has been and will be monitored in the future. At the same time, the causes for the poor breeding success, e.g. high nestling mortality, are investigated.
In the Swiss Black-headed Gull breeding colonies, breeding pair numbers and breeding success were assessed with the aid of volunteers between 2003 and 2006. In some of the breeding colonies, the effect of predation on the poor breeding success and the high nestling mortality was investigated by direct observations and infrared video cameras. Direct observations were conducted to analyse possible inter- and intra-specific competition as well as effects of weather conditions and disturbances by human activities. Blood metabolites were analysed to evaluate the nutritional condition of the nestlings. Some breeding colonies at Lake Zurich were equipped with webcams, which give interesting insights into the breeding activities of the Black-headed Gull.
With the popular colony-breeding Black-headed Gull we want to pinpoint the factors, which possibly affect a breeding population. Owing to this programme, supportive measures can be adjusted specifically to the Black-headed Gull. This is important because the Black-headed Gull is one of the 50 priority species in Switzerland, which rely on specific measures for their conservation.
Conservation measures should aim at the protection of existing natural and the enlargement of artificial breeding sites. On artificial breeding platforms, protection of nestling from predation and extreme weather events must be improved, which can be achieved by simple structural measures. Human activities can be minimised by creating ample protected zones or nature reserves.
Informations on the Black-headed Gull can be found in the popular scientific and richly illustrated book by Anderegg, K. & B. Walser (2007): "Weltenbummler und Sesshafte - Gefiederte am Zürichsee", Verlag Projektgruppe www.wasservoegel.ch.
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