Spring passerine migrants stopping over in the Sahara are not fall-outs

Abstract

The strategy of migrants crossing the Sahara desert has been the subject of debate, but recent evidence from radar studies has confirmed that most passerines use an intermittent migration strategy. The latter has also been suggested from previous studies in oases during autumn migration. It was found that migrants with relatively high fuel loads rest in the desert during daytime and continue migration during the following night, whereas lean migrants stopover in oases for several days to refuel. However, data from the Sahara are scarce for spring migration. We captured passerine migrants near Bîr Amrâne (22°47′N, 8°43′W) in the plain desert of Mauritania for 3 weeks during spring migration in 2004. We estimated flight ranges of 85 passerines stopping over in the desert to test whether they carried sufficient fuel loads to accomplish migration across the Sahara successfully. High fat loads of the majority of birds indicated that they were neither “fall-outs” nor too weak to accomplish migration successfully. The flight range estimates, based on mean flight speeds derived from radar measurements (59 km/h), revealed that 85% of all birds were able to reach the northern fringe of the desert with an intermittent migration strategy. Furthermore, birds stopping over in an oasis (Ouadâne, 370 km to the southwest of Bîr Amrâne) did not carry consistently lower fuel loads compared to the migrants captured in the desert.

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Acknowledgments

Mist-netting was only possible because of the help in the field of many volunteers, students, technicians and members of the Swiss Ornithological Institute, especially Alassan, F. Korner-Nievergelt, M. Liechti, V. Martignoli, A. Mauley and D. Zürrer whom we thank. Special thanks also to our indispensable local logistic team of Memoun, Mamadou, Bacar and Salem. The manuscript improved through discussion with B. Bruderer, L. Jenni and P. Jones. In Mauritania, invaluable assistance was given by the Ministry of Environment (MDRE), the Ministry of the Interior of Mauritania, the Centre for Locust Control (CLAA), German Technical Cooperation (GTZ), the Swiss Embassy in Algiers, the Swiss Honorary Consul and the German Embassy in Nouakchott. The Swiss Ornithological Institute’s project on Bird Migration across the Sahara was supported by the Swiss National Science Foundation (Project No. 31-65349), the Foundations Volkhart, Vontobel, MAVA for Nature Protection, Ernst Göhner, Felis and Syngenta and also by BirdLife Switzerland, BirdLife International, the companies Bank Sarasin & Co., Helvetia Patria Insurances and F. Hoffmann-La Roche AG. Further partners are listed on http://www.vogelwarte.ch/sahara.

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Correspondence to Volker Salewski.

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Communicated by H. Mouritsen.

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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

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Salewski, V., Schmaljohann, H. & Liechti, F. Spring passerine migrants stopping over in the Sahara are not fall-outs. J Ornithol 151, 371–378 (2010). https://doi.org/10.1007/s10336-009-0464-5

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Keywords

  • Flight range estimates
  • Intermittent migration
  • Sahara
  • Stop over
  • Passerines