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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The Re-establishment of ural owl strix uralensis in the bohemian forest
Auteurs :	Wolfgang Scherzinger, Auteur
Type de document :	Article
Dans :	Ornithologischer Anzeiger (45(2-3) DEC 2006)
Article en page(s) :	97-156
Résumé :	The Bohemian Forest straddles the upland border between Bavaria, the Czech Republic and Upper Austria. The Ural Owl is believed to have been extinct in the region since 1926, when the last bird was shot. With the foundation in 1970 of the Bavarian, Forest National Park within the Bohemian Forest belt, the possibility of re-establishing the original faunal diversity was discussed, e.g. by re-introduction of locally extinct species. The occurrence of Strix uralensis at this western fringe of the species' range represented a relict of post-glacial times, when forest spread over Central Europe. A reintroduction project relied on the release of young, captive-bred owls. The captive breeding stock consisted of owls from Sweden (4 male), Romania (2 female), Slovenia (2 male), Croatia, Finland, European Russia (1 male each) and Slovakia (1-2 female). From this foundation stock, between 5 and 11 breeding pairs were assembled in the National Park between 1972 and 2005, with a further 2 - 7 pairs elsewhere (zoo parks, rehabilitation centre, private keeper) during the same period. Since the first breeding success in 1973, 204 young Ural Owls have been reared (2 by hand, 202 by parent birds). Average date of first egg, March 21(st) (March 4(th) - April 16(th); n = 48); of hatching about April 22(nd) (n = 50); of leaving the nest-hole about May 24(th) (n = 38). Average clutch size (n = 93) was 2.4 eggs (max. 5-6), with average 3 eggs in replacement clutches. Ural Owl eggs are rather small in proportion to the body size of the female owl and measured 51.4 x 42.3 mm on average, smaller eggs overlapping in size those of the Tawny Owl Strix aluco.From this breeding programme, 212 Ural Owls (189 young birds and 23 older than 1 year) were released into the Bavarian Forest National Park between 1975 and 2005. Experiments with the adoption of 10 day old-nestlings by free-living Tawny Owls and four week old owlets by free-living Ural Owls were successful, but the use of Tawny Owls as foster parents exposed the risk of hybridisation in these sibling species. To aid establishment, food was presented near the release pen (to compensate for the lack of prey offered by parent birds) and about 60 large nest boxes were erected to bridge the lack of natural breeding sites in younger forest stands.Of 37 owls recovered (33 found dead and 4 weakened birds recaptured) most had died by electrocution or by collision with cars or forest fences (27%); a few individuals had been shot. Owls released in their first year dispersed 11.4 km on average (max. 52 km; n = 29). Above this age migratory behaviour disappears and older released birds moved only 2.7 km on average (n = 4). Based on 330 field observations and the monitoring of 29 radio-tagged owls, the preferred habitats can be defined as old mixed mountainous forest or old growth stands rich in beech trees, in climatically favourable settings, so long as these are interrupted by meadows, wind-blow glades or gaps resulting from insect infestation. The first wild breeding attempt occurred in 1985, the first successful breeding in 1989 (4 young). Between 1981 and 2005 a total of

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