Abstract

Numerous animals move vast distances through media with stochastic dynamic properties. Avian migrants must cope with variable wind speeds and directions en route, which potentially jeopardize fine-tuned migration routes and itineraries. We show how unpredictable winds affect flight times and the use of an intermediate staging site by red knots (Calidris canutus canutus) migrating from west Africa to the central north Siberian breeding areas via the German Wadden Sea. A dynamic migration model incorporating wind conditions during flight shows that flight durations between Mauritania and the Wadden Sea vary between 2 and 8 days. The number of birds counted at the only known intermediate staging site on the French Atlantic coast was strongly positively correlated with simulated flight times. In addition, particularly light-weight birds occurred at this location. These independent results support the idea that stochastic wind conditions are the main driver of the use of this intermediate stopover site as an emergency staging area. Because of the ubiquity of stochastically varying media, we expect such emergency habitats to exist in many other migratory systems, both airborne and oceanic. Our model provides a tool to quantify the effect of winds and currents en route.

Highlights

  • Migratory animals spend different parts of their lives in widely separated and ecologically distinct locations

  • Red knots staging in France were much lighter than any of the birds subsequently found in Germany (Dick et al 1987; Piersma et al 1992; van de Kam et al 2004), providing evidence that they had run out of energy stores and suggesting that they use the French inter-tidal areas as an emergency staging site

  • In systems like in the Afro-Siberian red knot system, where birds are unable to predict winds en route based on conditions at the onset of migration (Piersma et al 1990), they can either deposit extra fuel stores or make strategic use of emergency stopover sites, here provided by the Central French Atlantic coastal wetlands

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Summary

Introduction

Migratory animals spend different parts of their lives in widely separated and ecologically distinct locations. Their migratory movements can be very long, energetically costly and often take place in stochastically dynamic conditions (Dingle 1996; Liechti 2006; Chapman et al 2008; Gill et al 2009; Sale & Luschi 2009). As wind speeds are within the same order of magnitude as bird flight speeds, wind can have a strong impact on the cost and speed of migration (Liechti & Bruderer 1998; Shamoun-Baranes et al 2003). Canutus migrates north in two Electronic supplementary material is available at http://dx.doi.org/10. The Afro-Siberian nominate subspecies C. c. canutus migrates north in two Electronic supplementary material is available at http://dx.doi.org/10. 1098/rspb.2009.2112 or via http://rspb.royalsocietypublishing.org

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