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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Modelling the population dynamics of the Lesser Spotted Eagle Aquila pomarina in Brandenburg: What are the effects of years with extremely low reproduction?
Auteurs :	Torsten Langgemach, Auteur ; Joerg Boehner, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (132(2) 2011)
Article en page(s) :	93-100
Résumé :	Monitoring data for the Lesser Spotted Eagle Aquila pomarina in the federal state of Brandenburg (Germany) since 1994 indicate a continuous and significant decline of the species. In the recent past, several years with extraordinary poor reproductive success ("catastrophe years") have been noted in parts of the European breeding range, and unfavourable weather conditions during the incubation and nestling period, food shortage, and late arrival on the breeding sites are discussed as possible reasons. Because habitat alteration and climatic change may lead to a higher frequency of such years in the future, we analysed their impact on the long-term population dynamics, using a stochastic simulation (programme Vortex). Calculated were the effects of different frequencies of catastrophe years (occurring every 5(th), 10(th), 15(th), or 20(th) year) and of the degree to which the breeding success is lowered (20, 10, or 0% successful pairs, compared to 60% in normal years). In general, single years with extremely low reproduction have only a slight effect, but the impact increases with rising frequency and decreasing breeding success. The worst scenario calculated (0% every 5th year) indicates indeed a marked effect, leading to a decline from 46 individuals (population size in Brandenburg 2005) to only 15 individuals after 50 years, i.e. to 60% of the size of a control population without any catastrophe year. In such a case, the probability of extinction rises from a current 18% to 9.3%. Since most documented catastrophe years were linked to unfavourable weather conditions, the recent climatic change seems to form a considerable additional risk for smaller Lesser Spotted Eagle populations in the future. The actual impact is hard to predict but could be dramatic in conjunction with other threats, like habitat alteration and human persecution on the flyways.

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