The migration of the White Stork (Ciconia ciconia): a special case according to new data

To formulate a comprehensive plan for the conservation of the White Stork ( Ciconia ciconia) in conformity with the "Bonn Convention", along the easter n migration route from the breeding grounds across Israel into the staging areas in northeastern Africa, it was essential to investigate the entire pr ocess of migration, including resting behaviour as well as the energetic an d ecological aspects. Our approach employed satellite tracking (of 75 indiv iduals), observations of storks in aviaries by methods including magnetic r esonance imaging (MRI) and spectroscopy (MRS) (12 birds over 15 months), an d extensive field studies. The main result of the investigation is that the White Stork exhibits, at least on the eastern route, a particular mode of migration not previously described in this form for any bird species, with the following characteristics: (i) very rapid travel from the breeding regi on into the North African staging areas, normally with flight periods every day, lasting about 8-10 hours and separated by 14-16 hours of rest. The ca . 4 600-km distance to latitude 18 degreesN is covered in an average of 18- 19 days by both young and adult storks. (ii) Rest periods of a whole day or even several days are the exception, and their occurence seems to be promp ted by external circumstances rather than prescribed in the endogenous migr ation program. (iii) Body mass and fat deposition are low during the outwar d (and the homeward) journey and peak in midwinter, which is interpreted as an adaptation to unpredictable conditions in the winter quarters. (iv) The re is no discernible hyperphagia during migration;;instead, on the outward journey the storks evidently feed mainly to meet their immediate needs when in eastern Europe, more opportunistically when approaching the Mediterrane an Sea, and practically not at all in Israel. According to this observation and the comparison of body weights in Sachsen-Anhalt and Israel, it is lik ely that storks lose weight on the outward trip and do not regain it until they reach Africa. We call the migration mode of the White Stork, which tra vels predominantly in gliding flight, the MSOM type (from "mostly travellin g every day", "seldom inserting whole-day rests", "opportunistically feedin g" and "moderate or no fat depots developing"), and distinguish it from the types ILHB (for intermittently migrating) and NNHB (migrating non stop) (s ee Discussion). The results of this study, in particular regarding fat depo sition and state of breast musculature, are based substantially on MRI and MRS; these methods, tested here in a pioneering long-term study of a bird s pecies living in the wild, have proved extremely useful and show great prom ise (see following paper).