1. Department of Zoology; Edward Grey Institute of Field Ornithology; University of Oxford; South Parks Road Oxford OX1 3PS UK
2. Department of Anthropology (Evolutionary); University of California Davis; 1 Shields Avenue Davis CA 95616 USA
3. Smithsonian Tropical Research Institute; Ancon Panama
4. Department of Biology; Dalhousie University; 1355 Oxford St Halifax NS Canada B3H 4J1