Black-headed Gull

In this recovery programme, the causes of the drastic population decline of the Black-headed Gull are investigated and appropriate conservation measures worked out.

Aims

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.

Approach

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.

Significance

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.

Results

During the study period (2003–2006), the number of breeding pairs and breeding colonies slightly increased, although the total number of fledglings as well as the breeding success per pair decreased. Black-headed Gull populations in Switzerland are highly dependent on the demographic success of populations in the main breeding range of the species in northeastern Europe. Direct and video observations revealed that predation -at least in some colonies- negatively affected chick survival in the nestling stage. The hypothesis that nestlings suffer from lack of food was not supported, neither by measurements of body mass nor by the analysis of blood metabolite concentrations. Major nestling losses occurred during harsh weather periods with floods, storms and wet and cold conditions. Disturbances caused by human activities could be observed repeatedly and were thought to be most harmful during the nestling stage. Inter-specific competition occurred in the form of nest site competition with the Yellow-legged Gull, preventing the settlement of Black-backed Gulls. Intra-specific competition was mostly observed in densely populated breeding colonies.

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.

Project management

Martin Spiess

Partners

HSR Hochschule für Technik Rapperswil, Institute for Internet Technologies and Applications
Natur- und Vogelschutzverein Rapperswil-Jona
cnlab AG Rapperswil

Financial support

Stadt Rapperswil-Jona
Lotteriefonds des Kanton St. Gallen
Kurt Anderegg & Beat Walser (waived their author fee in favour of the project)

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