Der Zug des Weißstorchs (Ciconia ciconia): eine besondere Zugform auf Grund neuer Ergebnisse

Abstract

The migration of the White Stork (Ciconia ciconia): a special case according to new dataTo formulate a comprehensive plan for the conservation of the White Stork (Ciconia ciconia) in conformity with the "Bonn Convention", along the eastern migration route from the breeding grounds across Israel into the staging areas in northeastern Africa, it was essential to investigate the entire process of migration, including resting behaviour as well as the energetic and ecological aspects. Our approach employed satellite tracking (of 75 individuals), observations of storks in aviaries by methods including magnetic resonance imaging (MRI) and spectroscopy (MRS) (12 birds over 15 months), and 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 region 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°N 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 prompted by external circumstances rather than prescribed in the endogenous migration program. (iii) Body mass and fat deposition are low during the outward (and the homeward) journey and peak in midwinter, which is interpreted as an adaptation to unpredictable conditions in the winter quarters. (iv) There 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 Mediterranean 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 likely 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 travels predominantly in gliding flight, the MSOM type (from "mostly travelling every day", "seldom inserting whole-day rests", "opportunistically feeding" and "moderate or no fat depots developing"), and distinguish it from the types ILHB (for intermittently migrating) and NNHB (migrating non stop) (see Discus-J. Ornithol. 142, 73-92 (2001)  Deutsche Ornithologen-Gesellschaft/Blackwell Wissenschafts-Verlag, Berlin ISSN 0021-8375 U.S. Copyright Clearance Center Code Statement: 0021-8375/2001/14201-073 $ 15.00/0 sion). The results of this study, in particular regarding fat deposition 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 species living in the wild, have proved extremely useful and show great promise (see following paper).

Magnetic Resonance Imaging and Spectroscopy (MRI, MRS) of Seasonal Patterns of Body Composition: A Methodological Pilot Study in White Storks (Ciconia ciconia)

“…To measure the fat in the breast muscle spectroscopy was used to determine the fat : water ratio, from which changes in fat content could be derived. The study revealed pronounced seasonal changes in the visceral and cutaneous/subcutaneous fat depots, which precisely parallelled the annual variation in body weight of the birds (see also the preceding paper, Berthold et al 2001). The breast muscles exhibited the prolonged growth typical of the juveniles of large species but no conspicuous change at the migration periods.…”

Migratory orientation of first-year white storks (Ciconia ciconia): inherited information and social interactions

“…At this point, two birds were in central Sudan and one was in eastern Chad near the Sudanese border (Fig.·1). Their migration was very similar to the pattern shown by birds from NE Poland (Berthold et al, 2001a). The fourth bird stopped sending data at the beginning of August, before the onset of migration.…”

“…We assumed that the delayed storks made the directional change that normally occurs at the Gulf of Iskenderun (Berthold et al, 2001a) at the programmed date and took the south-southwest (SSW) course while still in Europe. However, the delayed birds differed from their non-manipulated conspecifics in two respects: (1) they were travelling alone and could rely on their innate orientation mechanisms only and (2) they were travelling late in the season when their conspecifics had (nearly) reached the first part of the wintering area in Africa.…”

“…To test this hypothesis, it was necessary to trace the route of the detained birds using satellite tracking (Berthold et al, 1997(Berthold et al, , 2001a. Satellite tracking has recently been applied to study the navigational abilities of green sea turtles (Luschi et al, 2001;Åkesson et al, 2003;Hays et al, 2003) and petrels (Benhamou et al, 2003).…”

Do White StorksCiconia ciconiaalways profit from an early return to their breeding grounds?

“…Recently White Storks from the Western European population (sensu Bairlein 1991) have started to overwinter in their breeding areas (Schulz 1998, Mata et al 2001. Moreover, some birds from the Eastern population have recently begun to halt their migration in southern Europe, notably in Bulgaria (Nankinov 1994), rather than continuing to their traditional wintering areas in sub-Saharan Africa (Berthold et al 2001). Hence, at least some individuals have a smaller migration distance and can return to their breeding areas earlier.…”