1. Division of Conservation Biology; Institute of Ecology and Evolution; University of Bern; Baltzerstrasse 6 3012 Bern Switzerland
2. School of Biological Sciences; The University of Queensland; St Lucia Qld 4072 Australia
3. CSIRO Land and Water Flagship; EcoSciences Precinct; Dutton Park Qld 4102 Australia
4. Swiss Ornithological Institute; Valais Field Station Rue du Rhône 11 1950 Sion Switzerland
5. Instituto Argentino de Investigaciones de las Zonas Áridas; CONICET; CC 507 5500 Mendoza Argentina