Ardea
Official journal of the Netherlands Ornithologists' Union

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Komenda-Zehnder S., Liechti F. & Bruderer B. (2002) Is reverse migration a common feature of nocturnal bird migration? An analysis of radar data from Israel. ARDEA 90 (2): 325-334
About 23 000 tracks of individual nocturnal migrants and density measurements in 131 nights were recorded by tracking radar at two sites in Israel during autumn 1991 and spring 1992. We used this data to analyse the occurrence of reverse migration in relation to weather and topography. Reverse migration was detected in all nights, on average representing a proportion of 5%. That the proportion of reverse movements was not related to weather factors, was probably due to the very stable weather conditions. Reverse migrants were not different from forward migrants with respect to their preference for flight altitudes with positive tailwinds and the species composition based on wing beat patterns. We suggest that apart from the reverse movements caused by adverse weather or ecological barriers ahead, unexpected flight directions may partly originate from the inaccuracy in orientation of the individual bird for single flight stages. Other factors influencing the scatter of flight directions may be search for appropriate stop over sites or the birds' actual physiological state


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