During migration, birds are often forced to cross ecological barriers, facing challenges due to scarcity of resources and suitable habitats. While crossing such barriers, birds are expected to adjust their behaviour to reduce time, energy expenditure and associated risks. We studied the crossing of the Sahara Desert by the Great White Pelican (Pelecanus onocrotalus), a large wetland-specialist. We focused on decisions made by migrating pelicans along different parts of the southbound autumn migration, their response to local environmental conditions and the implications for time and energy optimizations. We compared the observed pelicans' migration routes with simulated ‘direct-pass’ (shortest, mostly across the desert) and ‘corridor-pass’ (along the Nile River) routes, and used GPS, body acceleration and atmospheric modelling to compare flight behaviour along the Nile River versus the desert. The observed route was significantly shorter and faster than the simulated corridor-pass route and not significantly different from the simulated direct-pass one. Daily flights over the desert were longer than along the Nile River, with flying time extending to late hours of the day despite unfavourable atmospheric conditions for soaring–gliding flight. Moreover, the pelicans' behavioural response to atmospheric conditions changed according to the landscape over which they flew. Overall, the pelicans showed stronger behavioural adjustments to atmospheric conditions over the desert than along the Nile River. Our findings suggest that migrating pelicans primarily acted as time minimizers while crossing the Sahara Desert, whereas energetic optimization was only considered when it did not substantially compromise time optimization. The pelicans took the almost shortest possible route, only following the Nile River along its south-oriented parts, and frequently staged overnight in the desert far from water, despite being large, wet-habitat specialists. Correspondingly, their behavioural response to atmospheric conditions changed according to the landscape over which they were flying, switching between time (over the desert) and energy (over the Nile River) optimization strategies. Our results suggest that the interaction between landscape and atmospheric conditions depict a flexible, yet primarily time-dominated, migration optimization strategy. A free Plain Language Summary can be found within the Supporting Information of this article.
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We thank the Israeli Nature and Park Authority and its employees for their help in field work and for sharing their knowledge, especially to Ygal Miller, Yifat Artzi, Assaf Kaplan and Avishai Baron. We are grateful for Luca Maritan and Marry Megalli for retrieving a tag from a dead pelican in a remote area. Special thanks to the Movement Ecology Laboratory members and especially to Roi Harel and Shay Rotics for their help in data analyses, to Nir Horvitz for his help with the atmospheric model and to Sondra Turjeman with manuscript revision. We thank two anonymous reviewers and the editors of Functional Ecology for their constructive feedback. We would also like to acknowledge the Adelina and Massimo Della Pergola Chair of Life Sciences, the Minerva Center for Movement Ecology, the German-Israeli Foundation for Scientific Research and Development (GIF 999-66.8/2008), the German-Israeli Project Cooperation (DIP NA 846/1-1) and the United-States-Israel Binational Science Foundation (BSF 255/2008) and the Foundation Segré for their generous support. Finally, we would like to dedicate this paper to Shmulik Landau who passed away too young. His help in this research is a constant reminder of his love and dedication to wildlife. Research permits were obtained from the Israel Nature and Parks Authority (Ref. No.: 2012/002495, 2014/002495, 2015/002495).
© 2019 The Authors. Functional Ecology © 2019 British Ecological Society
- Nile River
- Sahara Desert
- animal behaviour
- movement ecology