1. Department of Biological Sciences, Virginia Polytechnic Institute and State University, Derring Hall, Blacksburg, VA 24061, USA
2. Unidade de Investigação em Eco-Etologia, Instituto Superior de Psicologia Aplicada, R. Jardim do Tabaco, n 34, 1149-049 Lisboa, Portugal
3. Department of Animal Ecology, Lund University, Ecology Building, 223 62 Lund, Sweden