Bruno Bruderer¹ & Sidney A. Gauthreaux Jr.²

1Swiss Ornithological Institute, CH-6204 Sempach, Switzerland, e-mail BrudererB@Orninst.ch; ²Department of Biological Sciences, Clemson University, South Carolina 29634-1903, USA, e-mail sagth@clemson.edu

Bruderer, B. & Gauthreaux Jr., S.A. 1999. Bird migration across large ecological barriers. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 1930. Johannesburg: BirdLife South Africa.

Opinions on the significance of ecological barriers, such as large water bodies, deserts and mountain ranges for migratory birds are controversial, particularly with respect to nocturnal migrants. Most authors assume that birds optimise tactics of barrier-crossing rather than make detours around unfavourable habitats. It is the aim of this symposium to examine for three regions (the Gulf of Mexico, the western Pacific and the threefold barrier of the Alps, the Mediterranean Sea, and the Sahara) the present knowledge on: (1) The quantitative significance of migration avoiding and crossing the barriers. (2) The significance of stepping stones, such as islands, coasts, oases, and low quality resting sites in deserts. (3) The variation in barrier crossing caused by weather, e.g. modifications in space and time, its adaptive significance through mortality. (4) Limits of crossing capacities.