Willem van den Bossche

Long-term satellite tracking sheds light upon variable migration strategies of White Storks (Ciconia ciconia)@@@Langzeit Satelliten-Telemetrie beim Weißstorch gibt Hinweise auf variable Zug- und Überwinterungsstrategien

During investigations on the migration of 120 individual White Storks by means of satellite tracking, four birds were tracked into their winter quarters several times, one bird on nine successive journeys. These storks did not exhibit strong winter-site fidelity, but instead occupied somewhat different winter quarters from one year to the next, probably depending on the food supply. Bisher konnten wir 120 Weißstörche auf ihrem Zug mit Hilfe der Satelliten-Telemetrie verfolgen, 4 Vögel mehrfach und einen auf neun aufeinander folgenden Wanderungen. Dabei zeichnet sich ab, dass Weißstörche im Gegensatz zu vielen anderen Afrikaziehern nur geringe Winterquartiertreue zeigen und im Laufe von Jahren in verschiedenen Gebieten überwintern, wahrscheinlich in Abh ängigkeit vom Nahrungsangebot.

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

To 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. 4600-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 occurrence 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 Discussion). 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). Für ein umfassendes Schutzkonzept für den Weißstorch (Ciconia ciconia) im Rahmen der „Bonner Konvention“ entlang der Ostroute von den Brutgebieten über Israel bis in nordostafrikanische Zwischenziele war es erforderlich, den genauen Zugablauf, das Rastverhalten sowie Fragen der Zugenergetik und Zugökologie zu untersuchen. Wir bearbeiteten die Fragen mit Hilfe der Satelliten-Telemetrie (75 Individuen), der Untersuchung von Störchen in Volieren einschließlich der Magnet-Resonanz-(MR-)Tomographie und -Spektroskopie (MRS) (12 Vögel, über 15 Monate) sowie umfangreicher Freilandstudien. Das Hauptergebnis der Untersuchungen ist: Der Weißstorch zeigt — zumindest auf der Ostroute — einen eigenartigen, bisher von keiner anderen Vogelart in dieser Form beschriebenen Zugmodus mit folgenden Charakteristika: 1) sehr zügiges, normalerweise tagtägliches Wandern vom Brutgebiet bis in die nordafrikanischen Zwischenziele, wobei täglich etwa 8–10 Stunden gewandert und 14–16 Stunden gerastet wird. Die rund 4 600 km bis zum 18. Breitengrad werden von Jung- wie Altstörchen im Mittel in 18–19 Tagen bewältigt. 2) Ganz- oder gar mehrtägige Rast wird nur ausnahmsweise eingeschoben und scheint eher durch äußere Umstände erzwungen als im endogenen Zugprogramm vorgegeben zu sein. 3) Körpermasse und Fettdeposition sind während des Wegzugs (und des Heimzugs) niedrig und erreichen Gipfelwerte im Mittwinter, die als Anpassung an unvorhersagbare Bedingungen im Winterquartier gedeutet werden. 4) Zugzeitliche Hyperphagie ist nicht erkennbar, vielmehr nehmen Störche während des Wegzugs Nahrung in Osteuropa wohl v. a. zur Deckung des Unterhaltsbedarfs auf, zum Mittelmeer hin mehr opportunistisch und in Israel so gut wie gar nicht. Dadurch und aus dem Vergleich von Körpermassen in Sachsen-Anhalt und Israel wird wahrscheinlich, dass Störche auf dem Wegzug an Masse verlieren, die dann erst in Afrika wieder aufgefüllt wird. Wir bezeichnen den Zugmodus des überwiegend im Gleitflug wandernden Weißstorchs als MSOM-Typ (von „Meist täglich wandernd“, „Selten ganze Rasttage einlegend“, „Opportunistisch Nahrung aufnehmend“ und „Maximal Mittelmäßige Fettdepots bildend“) und stellen ihm die Typen ILHB (für intermittierend ziehend) sowie NNHB (nonstop wandernd) gegenüber (s. Diskussion). Die Ergebnisse dieser Arbeit, v. a. über Fettdeposition und Brustmuskelzustand, beruhen ganz wesentlich auf der MR-Tomographie und MR-Spektroskopie, die hier in einer Lang-zeit-Pilotstudie an einer wild lebenden Vogelart zum Einsatz kam und sich als sehr nützlich und vielversprechend erwies (s. die nachfolgende Arbeit).

Satelliten-Telemetrie der Jahreswanderungen eines WeißstorchsCiconia ciconia und Diskussion der Orientierungsmechanismen des Heimzugs

In a female White Stork the complete migration cycle could be tracked by satellite from the nesting site to the wintering grounds in the Sudan and Tanzania and back to the nest. The migration route extended over 16 000 km, autumn migration lasted 100 days, homeward migration 70 days, wintering 58 and 41 days in northeastern and southeastern Africa, respectively. The maximum daily route was about 350 km. Up to Turkey the bird migrated together with its male. Homeward migration was performed within a relatively narrow corridor in which autumn migration took place, but in detail the routes of the two migratory seasons showed substantial differences. These data together with those from some raptors in which complete annual migration cycles could be tracked indicate that homeward migration is based on navigation (vector navigation and/or true navigation) rather than on route reversal.

Satelliten-Telemetrie beim WeißstorchCiconia ciconia: Wanderung eines Ost-Storchs in den Süd-Jemen@@@Satellite-tracking of White StorksCiconia cinonia: Migration of an eastern individual to South Yemen

Here we report on an unusual migratory route of a White Stork within the eastern migration corridor (east of the Central European migration divide) to the Arabian peninsula as far as South Yemen. White Storks migrating to and wintering in this area are scarce and their routes there and back — four being under discussion in the literature — are unknown. The 14-year-old breeding female from eastern Germany that we have investigated chose a route passing from Central Europe so far east as to touch the western Ukraine. Around the Gulf of Iskenderun the stork flew in the typical way, performing a migration bend to the right. But when passing Syria the stork again took an extremely easterly route. From the area of Damascus it did not follow the normal southwestern corridor through Jordan to Israel but flew in a southern direction to Saudi Arabia and along the eastern coast of the Red Sea to South Yemen. There, it was unfortunately shot. It remains open whether this migration-experienced adult bird made an orientation “error” in its old age or whether it might already have wintered on the Arabian peninsula in previous years.Here we report on an unusual migratory route of a White Stork within the eastern migration corridor (east of the Central European migration divide) to the Arabian peninsula as far as South Yemen. White Storks migrating to and wintering in this area are scarce and their routes there and back — four being under discussion in the literature — are unknown. The 14-year-old breeding female from eastern Germany that we have investigated chose a route passing from Central Europe so far east as to touch the western Ukraine. Around the Gulf of Iskenderun the stork flew in the typical way, performing a migration bend to the right. But when passing Syria the stork again took an extremely easterly route. From the area of Damascus it did not follow the normal southwestern corridor through Jordan to Israel but flew in a southern direction to Saudi Arabia and along the eastern coast of the Red Sea to South Yemen. There, it was unfortunately shot. It remains open whether this migration-experienced adult bird made an orientation “error” in its old age or whether it might already have wintered on the Arabian peninsula in previous years.

Satelliten-Telemetrie beim WeißstorchCiconia ciconia: Wanderung eines Ost-Storchs westlich bis Nigeria@@@Satellite-tracking of White Storks: Migration of an eastern individual westward as far as Nigeria

A male White Stork, for the first time equipped with a mini-transmitter operated by a solar battery, was tracked on the eastern migration route from E Germany to central African winter quarters and during part of the return migration, for a total distance of about 10 000 km. The individual moved westward into Nigeria, i.e. into the wintering area of western Storks. Since a number of other eastern Storks were tracked as far as Chad, the possibility is discussed that individuals migrating to central Africa along the eastern or western route may eventually return on the opposite route when attracted to flocks of the population from the other side of the migration divide. Some ringing recoveries are consistent with a U-shaped abmigration.