Meeting Abstract
76.2 Wednesday, Jan. 6 When skipping a high quality stopover site makes sense LEYRER, J*; ROBIN, F; DEKINGA, A; BRUGGE, M; SCHRIMPF, A; BOCHER, P; PIERSMA, T; University of Groningen; University of La Rochelle; Royal Netherlands Institution for Sea Rearch, Den Burg; Royal Netherlands Institution for Sea Rearch, Den Burg; Royal Netherlands Institution for Sea Rearch, Den Burg; University of La Rochelle; University of Groningen jutta.leyrer@nioz.nl
Many bird species migrate in a series of long-distance flights alternating with stopover periods where energy stores are accumulated. Stopover site use and optimal departure fuel loads have been the focus of many theoretical and empirical studies, suggesting that time-minimizing migrants should skip stopover sites with low or unpredictable food supplies. Departure fuel loads should enable birds to reach their destination. Carrying more fuel than necessary might be dangerous (higher predation risk) and is both time and energetically costly (storage or/and transport). Yet, overloading is a widespread phenomenon and is regarded as ‘safety net’ when conditions en route or upon arrival are unpredictable. The Afro-Siberian Red Knots Calidris c. canutus migrate from West Africa to central Siberia in two long-distance flights via the key staging site, the Schleswig-Holstein Wadden Sea, Germany. An annually varying number also stops at the central French Atlantic coast. We studied food resources for several years and show that the French stopover sites provide more predictable and better conditions to fuel than the main springboard for the last leg to the breeding grounds, the Wadden Sea. Despite the good food, in most years most Red Knots skip France. Body mass upon departure from Africa and arrival in the Wadden Sea indicate that some wind assistance is needed to reach the destination. But stochastic wind conditions prevent the birds from selecting a departure date coinciding with helping winds. We wonder why Knots do not overload in Africa in order to become more independent from wind assistance as well as to avoid an extra stopover in France.
