1. Cornell Lab of Ornithology , Ithaca, NY 14850-1923 , USA
2. Department of Biological Sciences, University of Toronto Scarborough , Scarborough ON, M1C 1A4 , Canada
3. Centre for Behavioural and Physiological Ecology, Zoology, University of New England , Armidale, New South Wales 2351 , Australia
4. Department of Biology, University of New Mexico College of Arts and Sciences , Albuquerque, NM 87131-0001 , USA
5. Max Planck Institute of Animal Behavior , Radolfzell 78315 , Germany
6. Department of Biology, University of Konstanz , Konstanz, 78457 , Germany
7. School of Biology and Ecology, University of Maine College of Natural Sciences Forestry and Agriculture , Orono, ME 04469-5735 , USA
8. School of Biological and Environmental Sciences, Liverpool John Moores University , Liverpool L33AF , UK