1. Dublin Zoo, Phoenix Park, D08 AC98 Dublin, Ireland
2. School of Biological Sciences, Queen’s University Belfast, Belfast BT9 5DL, UK
3. Centre for Research in Animal Behaviour, Psychology, University of Exeter, Exeter EX4 4QG, UK
4. Wildfowl & Wetlands Trust Ltd. (WWT), Slimbridge Wetland Centre, Gloucestershire GL2 7BT, UK