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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The development of a reintroduced population of White Storks Ciconia ciconia in the Rhineland-Palatinate and Saarland.
Auteurs :	Michael Stoltz, Auteur ; Hans-Wolfgang Helb, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (125(1) 2004)
Article en page(s) :	21-39
Résumé :	In 1997, a group called "Aktion PfalzStorch e.V. Bornheim" started a reintroduction project to transfer project storks into Rhineland-Palatinate. In 2002, the stork population consisted of 32 breeding pairs there, with an additional breeding pair in the adjacent Saarland (Fig. 1; for the percentages of the various types in each year see Fig. 3). By 2003 the population had increased to a total of 37 breeding pairs. Some critics disapproved of the use of project storks for this purpose, claiming that they have inadequate fitness and a poor ability to reproduce, as well as lacking a migratory drive and also being dependent on supplementary feeding. Furthermore it is feared that mating of project storks with wild storks could have a negative influence on the biorhythmicity and population genetics of wild stork stocks in the long term. On the example of the western Palatinate and the Saarpfalz-Kreis, we studied the migration of White Storks and the attractant effect of them on conspecifics (Fig. 4 and 5). It was possible to estimate a distance of c. 7 km over which the project storks had attracted conspecifics. Calculations indicated that the visual angle at which the migrating storks had detected their conspecifics was 30 seconds of arc. This value is discussed as evidence of the spatial visual ability of the White Stork. To investigate how the project storks would cope with life in the field, the prey-capture activities of project storks were monitored (Fig. 6). In winter supplementary food was given to the project storks as needed. Observations showed that even in winter, at least on frost-free days, the project storks independently searched for food and found it. In mild winters they could survive without any supplemented food. Within the study area, some differences were found in the foraging of project and wild storks in summer (Fig. 7). Comparison of breeding-biology parameters among project pairs, wild pairs and mixed pairs provided the following results (Figs. 8-12): The egg-laying period of the project pairs started significantly earlier than that of the wild and mixed pairs, but was still within the time span considered normal for the region's population. Between the distributions of clutch size and the numbers of hatched and fledged young no significant difference was found for the three pair types. The difference between overall and partial breeding success was not significant (Table 2). The latter parameters did not differ between the reintroduced population and the former population of the region (Table 3). It seems that the main reasons for the extinction of the former population were negative factors outside the breeding grounds. The juveniles produced by all three pair types migrated away from the breeding grounds at the usual time for the population of this area (Fig. 14). Furthermore, their arrival times were within the customary range (Fig. 15). On the basis of the present results and the interpretations of our findings with reference to the relevant literature, no evidence can be found that the project storks introduced to the study region have a negative influence on wild stork populations.

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