1. Division of Environmental and Evolutionary Biology, Graham Kerr Building, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK
2. Avian Science Research Centre, Scottish Agricultural College, Auchincruive, Ayr KA6 5HW, UK
3. Laboratoire de Parasitologie Evolutive, CNRS UMR 7103, Université Pierre et Marie Curie, Bâtiment, 7ème étage, 7 quai Saint Bernard, Case 237, F‐75252 Paris Cedex 05, France