1. University of St Andrews, Westburn Lane, KY16 9JP St Andrews, Scotland.
2. Behavioral Ecology and Ecophysiology Group, Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium.
3. Centre for Research and Conservation, Royal Zoological Society of Antwerp, K. Astridplein 26, B 2018 Antwerp, Belgium.
4. Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
5. Leipzig Research Centre for Early Child Development & Department for Early Child Development and Culture, Faculty of Education, Leipzig University, Jahnallee 59 04109, Germany.
6. Department of Cognitive Science, University of California, San Diego, 9500 Gilman Drive, La Jolla, San Diego, CA 92093, USA.