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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Results of colour-ringing White-tailed Sea Eagles Haliaeetus albicilla in Schleswig-Holstein: site fidelity, movements, dispersal, age of first breeding, age structure and breeding of siblings
Auteurs :	Bernd Struwe-Juhl, Auteur ; Thomas Gruenkorn, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (128(3) 2007)
Article en page(s) :	117-129
Résumé :	Between 1977 and 2006, 328 White-tailed Sea Eagle nestlings were ringed in Schleswig-Holstein (northern Germany) as part of the international colour-ringing programme. By the end of 2006, 139 ringed birds had been either resighted (92) or found dead (47). The overall recovery rate including resightings of colour-ringed birds is 37%, whereas the recovery rate of birds found dead was 12%. The majority of resightings (62%) were of immature birds (between the V and 4(th) calendar year), mainly seen between October and January at drained fish ponds. Almost all adults were identified between February and June on breeding territories.Young eagles dispersed in all directions. Birds in the 1(st), 2(nd) and 3(rd) calendar year wandered widely and mostly alone, only occasionally returning to their natal location. Birds in the 4(th) and 5(th) calendar year searched for a breeding territory close to their natal nest. This has become more difficult as the population density has increased and so young birds from Schleswig-Holstein have settled in neighbouring countries, establishing new breeding sites in Denmark, Poland and the Netherlands during the last ten years. Twenty-nine colour-ringed eagles are known to have established territories; 17 (59%) of these established territories within 100 km of their natal site. The median natal dispersal distance was 89 km and the maximum distance was 450 km.Of 270 individual birds identified in the field from their colour rings, 224 birds were from Schleswig-Holstein (83%) and 46 came from other regions, most of which were young eagles from Mecklenburg-Western Pomerania and Sweden. Only a few birds came from Finland and Poland. The probability of a ring recovery is strongly influenced by the distance from the ringing locality to Schleswig-Holstein, as well as by levels of ringing activity in these countries.Ring recoveries indicate that adult White-tailed Sea Eagles are monogamous and keep their territories for many years. The mean age of 35 breeding birds was 11.3 (s.d. 4.0) calendar years. In case one partner died or disappeared, males (n = 15) and females (n = 4) continued to occupy the same territories, breeding successfully with new partners. Recently, we have observed subadult eagles intruding on existing territories and even fighting with territorial adults. In one instance, an old territorial female resettled on a new territory 31 km away and bred successfully with a new male.Only three (out of 948) White-tailed Sea Eagles ringed in Mecklenburg-Western Pomerania settled in Schleswig-Holstein. Evidently, the population increase in Schleswig-Holstein can be attributed largely to the recruitment of locally-bred young. Two males and two females from the breeding population of Schleswig-Holstein bred for the first time at the age of three years (in the 4(th) calendar year) compared with the average age of 4.4 years. In 2002 we recorded a successful breeding attempt in the wild by eagles that were siblings (from the same nest and year).

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