Orientation of passerine trans-Sahara migrants: the directional shift (‘Zugknick’) reconsidered for free-flying birds

doi:10.1016/j.anbehav.2011.10.005

Animal Behaviour

Volume 83, Issue 1, January 2012, Pages 63-68

https://doi.org/10.1016/j.anbehav.2011.10.005 Get rights and content

As most long-distance migrants leave their breeding ranges in Western Europe towards the southwest, they must change their migratory directions somewhere to reach their nonbreeding areas in Africa. Laboratory experiments have been the basis to suggest an endogenously controlled, abrupt directional shift in the south of the Iberian Peninsula, the so-called ‘Zugknick’. We compared own radar data gathered in Europe and the Western Sahara with this established theory. Radar tracks were filtered according to the wing beat pattern and migratory passage of garden warblers, Sylvia borin, and pied flycatchers, Ficedula hypoleuca, the species used in the former experiments. The flight directions were highly concentrated and the mean direction in the Western Sahara was only slightly more south than the southwesterly directions in central and southwestern Europe. At observation sites close to the southern edge of the Sahara, mean directions were south to east-southeast. We therefore conclude that an endogenously predetermined directional shift occurs towards the end of the Sahara crossing according to physiological or environmental triggers leading the birds towards their wintering ranges in the southeast.

Highlights

► Flight directions of European passerines along the western flyway to Africa. ► Testing orientation mechanisms based on field observations. ► Gradual shift of migratory direction until the end of Sahara crossing. ► Change of migratory direction after the Sahara crossing. ► Results from laboratory orientation experiments reconsidered.

Section snippets

Capture Data from Mauritania

We used capture data gathered in 2003 to determine the timing of the migratory passage of pied flycatchers and garden warblers in southern Mauritania. Birds were captured at different sites in the vicinity of the radar sites (Fig. 1) with standard mist-nets between 13 August and 26 October (Salewski et al. 2009). We calculated standardized daily trapping numbers by accounting for trapping effort. Out of a total of 10 573 individuals (recaptures of the same season at the same site were

Results

Along the latitudinal range of the study sites, all theoretical models predict a gradual shift from southwest towards more southerly directions (Fig. 2). The shift caused by a constant magnetic north route is less than 10° from the constant geographical direction. Migrants orienting along a magnetoclinic route would make the strongest shift, ending up with a due south direction at the end of the Sahara crossing. The great circle route and the sun compass route predict directions in between the

Discussion

To investigate flight behaviour with respect to orientation, we would prefer to look at long tracks of individual birds, rather than at the general flight directions at different sites along the migratory route. However, our results are based on representative samples of small passerines migrating along the western Palaearctic–African flyway including the two very common species, garden warbler and pied flycatcher. Because flight directions were highly concentrated at almost all sites, there is

Acknowledgments

We are deeply indebted to colleagues, volunteers and students who spent hundreds of hours collecting radar data in various projects around Europe and Africa. Through all the years Thomas Steuri maintained and improved our bird radar system; he and Erich Bächler developed the specific software to analyse the data. We acknowledge the ringing team that contributed new data on the migratory phenology in Mauritania, particularly Marc Herremans, Fränzi and Pius Korner-Nievergelt, Heiko Schmaljohann

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View full text

Orientation of passerine trans-Sahara migrants: the directional shift (‘Zugknick’) reconsidered for free-flying birds

Highlights

Section snippets

Capture Data from Mauritania

Results

Discussion

Acknowledgments

Journal of Theoretical Biology

Bird Migration

Ökosystemanalyse der Rastplätze von Zugvögeln: Beschreibung und Deutung der Verteilungsmuster von ziehenden Kleinvögeln in verschiedenen Biotopen der Stationen des ‘Mettnau-Reit-Illmitz-Programmes’

Ökologie der Vögel

Offene Fragen der Erforschung des Zuges paläarktischer Vogelarten in Afrika

Vogelwarte

Magnetic factors control the migratory direction of pied flycatchers (Ficedula hypoleuca Pallas)

Vogelzug: eine Einführung und kurze aktuelle Gesamtübersicht

Bird Migration: a General Survey

Migratory directions of birds under the influence of wind and topography

Flight behaviour of nocturnally migrating birds in coastal areas: crossing or coasting

Journal of Avian Biology

Bird migration across the Mediterranean

Wing-beat characteristics of birds recorded with tracking radar and cine camera

Ibis

Birds of the Strait of Gibraltar

Variation in the nocturnal flight behaviour of migratory birds along the northwest coast of the Mediterranean Sea

Ibis

Handbuch der Vögel Mitteleuropas. Bd.12. Passeriformes (3. Teil)

Handbuch der Vögel Mitteleuropas. Bd.13. Passeriformes (4. Teil)

Circannual Rhythms. Endogenous Annual Clocks in the Organization of Seasonal Processes

Endogenously controlled changes in migratory direction of the garden warbler, Sylvia borin

Journal of Comparative Physiology

The natural link between Europe and Africa: 2.1 billion birds on migration

Oikos

Migratory orientation of blackcaps (Sylvia atricapilla): population-specific shifts of direction during the autumn

Ethology

Radar observations of passerine trans-Saharan migrants in southern Portugal

Ardeola

Autumn migration of trans-Saharan migrating passerines in the straits of Gibraltar

The Auk